M48T35 M48T35Y ® 5 V, 256 Kbit (32 Kb x 8) TIMEKEEPER SRAM Features ■ Integrated, ultra low power SRAM, real-time clock, power-fail control circuit and battery ■ BYTEWIDE™ RAM-like clock access ■ BCD coded year, month, day, date, hours, 28 minutes, and seconds 1 ■ Frequency test output for real-time clock ■ Automatic power-fail chip deselect and WRITE protection PCDIP28 Battery/crystal ■ WRITE protect voltages CAPHAT™ V = power-fail deselect voltage): PFD – M48T35: V = 4.75 to 5.5 V; CC 4.5 V ≤ V ≤ 4.75 V PFD – M48T35Y: V = 4.5 to 5.5 V; SNAPHAT® CC 4.2 V ≤ V ≤ 4.5 V Battery/crystal PFD ■ Self-contained battery and crystal in the CAPHAT™ DIP package ■ SOIC package provides direct connection for a SNAPHAT® housing containing the battery and crystal ■ SNAPHAT® housing (battery and crystal) is replaceable 28 ■ Pin and function compatible with JEDEC 1 standard 32 Kb x 8 SRAMs SOH28 ■ RoHS compliant – Lead-free second level interconnect June 2011 Doc ID 2611 Rev 10 1/28 www.st.com 1

Contents M48T35, M48T35Y Contents 1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 Operation modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1 READ mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2 WRITE mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.3 Data retention mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3 Clock operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.1 Reading the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.2 Setting the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.3 Stopping and starting the oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.4 Calibrating the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3.5 Century bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.6 V noise and negative going transients . . . . . . . . . . . . . . . . . . . . . . . . . 16 CC 4 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5 DC and AC parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 7 Part numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 8 Environmental information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2/28 Doc ID 2611 Rev 10

M48T35, M48T35Y List of tables List of tables Table 1. Signal names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Table 2. Operating modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Table 3. READ mode AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Table 4. WRITE mode AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Table 5. Register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Table 6. Absolute maximum ratings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Table 7. Operating and AC measurement conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Table 8. Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Table 9. DC characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Table 10. Power down/up AC characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Table 11. Power down/up trip points DC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Table 12. PCDIP28 – 28-pin plastic DIP, battery CAPHAT™, package mech. data . . . . . . . . . . . . . 21 Table 13. SOH28 – 28-lead plastic SO, 4-socket battery SNAPHAT®, package mechanical data . . 22 Table 14. SH – 4-pin SNAPHAT® housing for 48 mAh battery & crystal, package mechanical data. 23 Table 15. SH – 4-pin SNAPHAT® housing for 120 mAh battery & crystal, package mechanical data24 Table 16. Ordering information scheme. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Table 17. SNAPHAT® battery table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Table 18. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Doc ID 2611 Rev 10 3/28

List of figures M48T35, M48T35Y List of figures Figure 1. Logic diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Figure 2. DIP connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Figure 3. SOIC connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Figure 4. Block diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Figure 5. READ mode AC waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Figure 6. WRITE enable controlled, WRITE AC waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Figure 7. Chip enable controlled, WRITE AC waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Figure 8. Crystal accuracy across temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Figure 9. Clock calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Figure 10. Supply voltage protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Figure 11. AC measurement load circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 12. Power down/up mode AC waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Figure 13. PCDIP28 – 28-pin plastic DIP, battery CAPHAT™, package outline. . . . . . . . . . . . . . . . . 21 Figure 14. SOH28 – 28-lead plastic small outline, 4-socket battery SNAPHAT®, package outline. . . 22 Figure 15. SH – 4-pin SNAPHAT® housing for 48 mAh battery & crystal, package outline. . . . . . . . . 23 Figure 16. SH – 4-pin SNAPHAT® housing for 120 mAh battery & crystal, package outline. . . . . . . . 24 Figure 17. Recycling symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 4/28 Doc ID 2611 Rev 10

M48T35, M48T35Y Description 1 Description The M48T35/Y TIMEKEEPER® RAM is a 32 Kb x 8 non-volatile static RAM and real-time clock. The monolithic chip is available in two special packages to provide a highly integrated battery-backed memory and real-time clock solution. The M48T35/Y is a non-volatile pin and function equivalent to any JEDEC standard 32 Kb x 8 SRAM. It also easily fits into many ROM, EPROM, and EEPROM sockets, providing the non-volatility of PROMs without any requirement for special WRITE timing or limitations on the number of WRITEs that can be performed. The 28-pin, 600 mil DIP CAPHAT™ houses the M48T35/Y silicon with a quartz crystal and a long life lithium button cell in a single package. The 28-pin, 330 mil SOIC provides sockets with gold plated contacts at both ends for direct connection to a separate SNAPHAT® housing containing the battery and crystal. The unique design allows the SNAPHAT battery package to be mounted on top of the SOIC package after the completion of the surface mount process. Insertion of the SNAPHAT housing after reflow prevents potential battery and crystal damage due to the high temperatures required for device surface-mounting. The SNAPHAT housing is keyed to prevent reverse insertion. The SOIC and battery/crystal packages are shipped separately in plastic anti-static tubes or in tape & reel form. For the 28-lead SOIC, the battery/crystal package (e.g., SNAPHAT) part number is “M4T28- BR12SH”. Figure 1. Logic diagram VCC 15 8 A0-A14 DQ0-DQ7 W M48T35 M48T35Y E G VSS AI01620B Doc ID 2611 Rev 10 5/28

Description M48T35, M48T35Y Table 1. Signal names A0-A14 Address inputs DQ0-DQ7 Data inputs / outputs E Chip enable G Output enable W WRITE enable V Supply voltage CC V Ground SS Figure 2. DIP connections A14 1 28 VCC A12 2 27 W A7 3 26 A13 A6 4 25 A8 A5 5 24 A9 A4 6 23 A11 A3 7 22 G M48T35 A2 8 M48T35Y 21 A10 A1 9 20 E A0 10 19 DQ7 DQ0 11 18 DQ6 DQ1 12 17 DQ5 DQ2 13 16 DQ4 VSS 14 15 DQ3 AI01621B Figure 3. SOIC connections A14 1 28 VCC A12 2 27 W A7 3 26 A13 A6 4 25 A8 A5 5 24 A9 A4 6 23 A11 A3 7 22 G M48T35Y A2 8 21 A10 A1 9 20 E A0 10 19 DQ7 DQ0 11 18 DQ6 DQ1 12 17 DQ5 DQ2 13 16 DQ4 VSS 14 15 DQ3 AI01622B 6/28 Doc ID 2611 Rev 10

M48T35, M48T35Y Description Figure 4. Block diagram OSCILLATOR AND 8 x 8 BiPORT CLOCK CHAIN SRAM ARRAY 32,768 Hz CRYSTAL A0-A14 POWER DQ0-DQ7 32,760 x 8 SRAM ARRAY LITHIUM CELL E VOLTAGE SENSE AND VPFD W SWITCHING G CIRCUITRY VCC VSS AI01623 Doc ID 2611 Rev 10 7/28

Operation modes M48T35, M48T35Y 2 Operation modes As Figure4 on page7 shows, the static memory array and the quartz controlled clock oscillator of the M48T35/Y are integrated on one silicon chip. The two circuits are interconnected at the upper eight memory locations to provide user accessible BYTEWIDE clock information in the bytes with addresses 7FF8h-7FFFh. The clock locations contain the year, month, date, day, hour, minute, and second in 24-hour BCD format. Corrections for 28, 29 (leap year - valid until 2100), 30, and 31 day months are made automatically. Byte 7FF8h is the clock control register. This byte controls user access to the clock information and also stores the clock calibration setting. The eight clock bytes are not the actual clock counters themselves; they are memory locations consisting of BiPORT™ READ/WRITE memory cells. The M48T35/Y includes a clock control circuit which updates the clock bytes with current information once per second. The information can be accessed by the user in the same manner as any other location in the static memory array. The M48T35/Y also has its own power-fail detect circuit. The control circuitry constantly monitors the single 5 V supply for an out of tolerance condition. When V is out of CC tolerance, the circuit write protects the SRAM, providing a high degree of data security in the midst of unpredictable system operation brought on by low V . As V falls below the CC CC battery backup switchover voltage (V ), the control circuitry connects the battery which SO maintains data and clock operation until valid power returns. Table 2. Operating modes Mode V E G W DQ0-DQ7 Power CC Deselect V X X High Z Standby IH 4.75 to 5.5 V WRITE V X V D Active IL IL IN or READ V V V D Active 4.5 to 5.5 V IL IL IH OUT READ V V V High Z Active IL IH IH Deselect V to V (min)(1) X X X High Z CMOS standby SO PFD Deselect ≤ V (1) X X X High Z Battery backup mode SO 1. See Table11 on page20 for details. X = V or V ;V = battery backup switchover voltage. IH IL SO 2.1 READ mode The M48T35/Y is in the READ mode whenever W (WRITE enable) is high and E (chip enable) is low. The unique address specified by the 15 address inputs defines which one of the 32,768 bytes of data is to be accessed. Valid data will be available at the data I/O pins within address access time (t ) after the last address input signal is stable, providing that AVQV the E and G access times are also satisfied. If the E and G access times are not met, valid data will be available after the latter of the chip enable access time (t ) or output enable access time (t ). ELQV GLQV The state of the eight three-state data I/O signals is controlled by E and G. If the outputs are activated before t , the data lines will be driven to an indeterminate state until t . AVQV AVQV 8/28 Doc ID 2611 Rev 10

M48T35, M48T35Y Operation modes If the address inputs are changed while E and G remain active, output data will remain valid for output data hold time (t ) but will go indeterminate until the next address access. AXQX Figure 5. READ mode AC waveforms tAVAV A0-A14 VALID tAVQV tAXQX tELQV tEHQZ E tELQX tGLQV tGHQZ G tGLQX DQ0-DQ7 VALID AI00925 Note: WRITE enable (W) = high. Table 3. READ mode AC characteristics M48T35/Y Symbol Parameter(1) Unit Min Max t READ cycle time 70 ns AVAV t Address valid to output valid 70 ns AVQV t Chip enable low to output valid 70 ns ELQV t Output enable low to output valid 35 ns GLQV t (2) Chip enable low to output transition 5 ns ELQX t (2) Output enable low to output transition 5 ns GLQX t (2) Chip enable high to output Hi-Z 25 ns EHQZ t (2) Output enable high to output Hi-Z 25 ns GHQZ t Address transition to output transition 10 ns AXQX 1. Valid for ambient operating temperature: T = 0 to 70 or –40 to 85 °C; V = 4.75 to 5.5 V or 4.5 to 5.5 V (except where A CC noted). 2. C = 5 pF. L Doc ID 2611 Rev 10 9/28

Operation modes M48T35, M48T35Y 2.2 WRITE mode The M48T35/Y is in the WRITE mode whenever W and E are low. The start of a WRITE is referenced from the latter occurring falling edge of W or E. A WRITE is terminated by the earlier rising edge of W or E. The addresses must be held valid throughout the cycle. E or W must return high for a minimum of t from chip enable or t from WRITE enable prior EHAX WHAX to the initiation of another READ or WRITE cycle. Data-in must be valid t prior to the DVWH end of WRITE and remain valid for t afterward. G should be kept high during WRITE WHDX cycles to avoid bus contention; although, if the output bus has been activated by a low on E and G, a low on W will disable the outputs t after W falls. WLQZ Figure 6. WRITE enable controlled, WRITE AC waveform tAVAV A0-A14 VALID tAVWH tAVEL tWHAX E tWLWH tAVWL W tWLQZ tWHQX tWHDX DQ0-DQ7 DATA INPUT tDVWH AI00926 Figure 7. Chip enable controlled, WRITE AC waveforms tAVAV A0-A14 VALID tAVEH tAVEL tELEH tEHAX E tAVWL W tEHDX DQ0-DQ7 DATA INPUT tDVEH AI00927 10/28 Doc ID 2611 Rev 10

M48T35, M48T35Y Operation modes Table 4. W RITE mode AC characteristics M48T35/Y Symbol Parameter(1) Unit Min Max t WRITE cycle time 70 ns AVAV t Address valid to WRITE enable low 0 ns AVWL t Address valid to chip enable low 0 ns AVEL t WRITE enable pulse width 50 ns WLWH t Chip enable low to chip enable high 55 ns ELEH t WRITE enable high to address transition 0 ns WHAX t Chip enable high to address transition 0 ns EHAX t Input valid to WRITE enable high 30 ns DVWH t Input valid to chip enable high 30 ns DVEH t WRITE enable high to input transition 5 ns WHDX t Chip enable high to input transition 5 ns EHDX t (2)(3) WRITE enable low to output Hi-Z 25 ns WLQZ t Address valid to WRITE enable high 60 ns AVWH t Address valid to chip enable high 60 ns AVEH t (2)(3) WRITE enable high to output transition 5 ns WHQX 1. Valid for ambient operating temperature: T = 0 to 70 or –40 to 85 °C; V = 4.75 to 5.5 V or 4.5 to 5.5 V (except where A CC noted). 2. C = 5 pF. L 3. If E goes low simultaneously with W going low, the outputs remain in the high impedance state. 2.3 Data retention mode With valid V applied, the M48T35/Y operates as a conventional BYTEWIDE static RAM. CC Should the supply voltage decay, the RAM will automatically power-fail deselect, write protecting itself when V falls within the V (max), V (min) window. All outputs CC PFD PFD become high impedance, and all inputs are treated as “Don't care” (see Figure12 on page19, Table10, and Table11 on page20). Note: A power failure during a WRITE cycle may corrupt data at the currently addressed location, but does not jeopardize the rest of the RAM's content. At voltages below V (min), the PFD user can be assured the memory will be in a write protected state, provided the V fall time CC is not less than t . The M48T35/Y may respond to transient noise spikes on V that reach F CC into the deselect window during the time the device is sampling V . Therefore, decoupling CC of the power supply lines is recommended. When V drops below V , the control circuit switches power to the internal battery which CC SO preserves data and powers the clock. The internal button cell will maintain data in the M48T35/Y for an accumulated period of at least 7 years when V is less than V . As CC SO system power returns and V rises above V , the battery is disconnected, and the power CC SO supply is switched to external V . Write protection continues until V reaches V (min) CC CC PFD plus t (min). E should be kept high as V rises past V (min) to prevent inadvertent rec CC PFD WRITE cycles prior to processor stabilization. Normal RAM operation can resume t after rec V exceeds V (max). CC PFD For more information on battery storage life refer to the application note AN1012. Doc ID 2611 Rev 10 11/28

Clock operations M48T35, M48T35Y 3 Clock operations 3.1 Reading the clock Updates to the TIMEKEEPER® registers (see Table5) should be halted before clock data is read to prevent reading data in transition. The BiPORT™ TIMEKEEPER cells in the RAM array are only data registers and not the actual clock counters, so updating the registers can be halted without disturbing the clock itself. Updating is halted when a '1' is written to the READ bit, D6 in the control register 7FF8h. As long as a '1' remains in that position, updating is halted. After a halt is issued, the registers reflect the count; that is, the day, date, and the time that were current at the moment the halt command was issued. All of the TIMEKEEPER registers are updated simultaneously. A halt will not interrupt an update in progress. Updating is within a second after the bit is reset to a '0.' 3.2 Setting the clock Bit D7 of the control register 7FF8h is the WRITE bit. Setting the WRITE bit to a '1,' like the READ bit, halts updates to the TIMEKEEPER® registers. The user can then load them with the correct day, date, and time data in 24-hour BCD format (see Table5). Resetting the WRITE bit to a '0' then transfers the values of all time registers 7FF9h-7FFFh to the actual TIMEKEEPER counters and allows normal operation to resume. The FT bit and the bits marked as '0' in Table5 must be written to '0' to allow for normal TIMEKEEPER and RAM operation. After the WRITE bit is reset, the next clock update will occur within one second. See the application note AN923, “TIMEKEEPER® Rolling Into the 21st Century” for information on century rollover. 3.3 Stopping and starting the oscillator The oscillator may be stopped at any time. If the device is going to spend a significant amount of time on the shelf, the oscillator can be turned off to minimize current drain on the battery. The STOP bit is the MSB of the seconds register. Setting it to a '1' stops the oscillator. The M48T35/Y is shipped from STMicroelectronics with the STOP bit set to a '1.' When reset to a '0,' the M48T35/Y oscillator starts within 1 second. 12/28 Doc ID 2611 Rev 10

M48T35, M48T35Y Clock operations Table 5. Register map Data Function/range Address D7 D6 D5 D4 D3 D2 D1 D0 BCD format 7FFFh 10 Years Year Year 00-99 7FFEh 0 0 0 10 M. Month Month 01-12 7FFDh 0 0 10 date Date Date 01-31 Century/ 7FFCh 0 FT CEB CB 0 Day 00-01/01-07 day 7FFBh 0 0 10 hours Hours Hours 00-23 7FFAh 0 10 minutes Minutes Minutes 00-59 7FF9h ST 10 seconds Seconds Seconds 00-59 7FF8h W R S Calibration Control Keys: S = SIGN bit FT = FREQUENCY TEST bit (must be set to '0' upon power for normal operation) R = READ bit W = WRITE bit ST = STOP bit 0 = Must be set to '0' CEB = CENTURY ENABLE bit CB = CENTURY bit Note: When CEB is set to '1,' CB will toggle from '0' to '1' or from '1' to '0' at the turn of the century (dependent upon the initial value set). When CEB is set to '0,' CB will not toggle. The WRITE bit does not need to be set to write to CEB. 3.4 Calibrating the clock The M48T35/Y is driven by a quartz-controlled oscillator with a nominal frequency of 32,768 Hz. The devices are tested not to exceed 35 ppm (parts per million) oscillator frequency error at 25 °C, which equates to about ±1.53 minutes per month. With the calibration bits properly set, the accuracy of each M48T35/Y improves to better than +1/–2 ppm at 25 °C. The oscillation rate of any crystal changes with temperature (see Figure8 on page15). Most clock chips compensate for crystal frequency and temperature shift error with cumbersome “trim” capacitors. The M48T35/Y design, however, employs periodic counter correction. The calibration circuit adds or subtracts counts from the oscillator divider circuit at the divide by 256 stage, as shown in Figure9 on page15. The number of times pulses are blanked (subtracted, negative calibration) or split (added, positive calibration) depends upon the value loaded into the five calibration bits found in the control register. Adding counts speeds the clock up, subtracting counts slows the clock down. The calibration byte occupies the five lower order bits (D4-D0) in the control register 7FF8h. These bits can be set to represent any value between 0 and 31 in binary form. Bit D5 is the Doc ID 2611 Rev 10 13/28

Clock operations M48T35, M48T35Y sign bit; '1' indicates positive calibration, '0' indicates negative calibration. Calibration occurs within a 64 minute cycle. The first 62 minutes in the cycle may, once per minute, have one second either shortened by 128 or lengthened by 256 oscillator cycles. If a binary '1' is loaded into the register, only the first 2 minutes in the 64 minute cycle will be modified; if a binary 6 is loaded, the first 12 will be affected, and so on. Therefore, each calibration step has the effect of adding 512 or subtracting 256 oscillator cycles for every 125,829,120 actual oscillator cycles, that is +4.068 or –2.034 ppm of adjustment per calibration step in the calibration register. Assuming that the oscillator is in fact running at exactly 32,768 Hz, each of the 31 increments in the calibration byte would represent +10.7 or –5.35 seconds per month which corresponds to a total range of +5.5 or –2.75 minutes per month. Two methods are available for ascertaining how much calibration a given M48T35/Y may require. The first involves simply setting the clock, letting it run for a month and comparing it to a known accurate reference (like WWV broadcasts). While that may seem crude, it allows the designer to give the end user the ability to calibrate his clock as his environment may require, even after the final product is packaged in a non-user serviceable enclosure. All the designer has to do is provide a simple utility that accesses the calibration byte. The second approach is better suited to a manufacturing environment, and involves the use of some test equipment. When the frequency test (FT) bit, the seventh-most significant bit in the day register is set to a '1,' and D7 of the seconds register is a '0' (oscillator running), DQ0 will toggle at 512 Hz during a READ of the seconds register. Any deviation from 512 Hz indicates the degree and direction of oscillator frequency shift at the test temperature. For example, a reading of 512.01024 Hz would indicate a +20 ppm oscillator frequency error, requiring a –10 (WR001010) to be loaded into the calibration byte for correction. Note: Setting or changing the calibration byte does not affect the frequency test output frequency. The FT bit MUST be reset to '0' for normal clock operations to resume. The FT bit is automatically reset on power-down. For more information on calibration, see application note AN934, “TIMEKEEPER® Calibration.” 3.5 Century bit Bit D5 and D4 of clock register 1FFCh contain the CENTURY ENABLE bit (CEB) and the CENTURY bit (CB). Setting CEB to a '1' will cause CB to toggle, either from a '0' to '1' or from '1' to '0' at the turn of the century (depending upon its initial state). If CEB is set to a '0,' CB will not toggle. Note: The WRITE bit must be set in order to write to the CENTURY bit. 14/28 Doc ID 2611 Rev 10

M48T35, M48T35Y Clock operations Figure 8. Crystal accuracy across temperature ppm 20 0 -20 -40 ΔF = -0.038 ppm(T - T)2 ± 10% F C2 0 -60 T = 25 °C 0 -80 -100 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 °C AI02124 Figure 9. Clock calibration NORMAL POSITIVE CALIBRATION NEGATIVE CALIBRATION AI00594B Doc ID 2611 Rev 10 15/28

Clock operations M48T35, M48T35Y 3.6 V noise and negative going transients CC I transients, including those produced by output switching, can produce voltage CC fluctuations, resulting in spikes on the V bus. These transients can be reduced if CC capacitors are used to store energy which stabilizes the V bus. The energy stored in the CC bypass capacitors will be released as low going spikes are generated or energy will be absorbed when overshoots occur. A bypass capacitor value of 0.1 µF (as shown in Figure10) is recommended in order to provide the needed filtering. In addition to transients that are caused by normal SRAM operation, power cycling can generate negative voltage spikes on V that drive it to values below V by as much as CC SS one volt. These negative spikes can cause data corruption in the SRAM while in battery backup mode. To protect from these voltage spikes, it is recommended to connect a Schottky diode from V to V (cathode connected to V , anode to V ). Schottky diode CC SS CC SS 1N5817 is recommended for through hole and MBRS120T3 is recommended for surface mount. Figure 10. Supply voltage protection VCC VCC 0.1µF DEVICE VSS AI02169 16/28 Doc ID 2611 Rev 10

M48T35, M48T35Y Maximum ratings 4 Maximum ratings Stressing the device above the rating listed in the absolute maximum ratings table may cause permanent damage to the device. These are stress ratings only and operation of the device at these or any other conditions above those indicated in the operating sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Table 6. Absolute maximum ratings Symbol Parameter Value Unit Grade 1 0 to 70 °C T Ambient operating temperature A Grade 6 –40 to 85 °C T Storage temperature (V off, oscillator off) –40 to 85 °C STG CC T (1)(2)(3) Lead solder temperature for 10 seconds 260 °C SLD M48T35 –0.3 to 7 V V Input or output voltages IO M48T35Y –0.3 to 7 V M48T35 –0.3 to 7 V V Supply voltage CC M48T35Y –0.3 to 7 V I Output current 20 mA O P Power dissipation 1 W D 1. For DIP package, soldering temperature of the IC leads is to not exceed 260 °C for 10 seconds. Furthermore, the devices shall not be exposed to IR reflow nor preheat cycles (as performed as part of wave soldering). ST recommends the devices be hand-soldered or placed in sockets to avoid heat damage to the batteries. 2. For DIP packaged devices, ultrasonic vibrations should not be used for post-solder cleaning to avoid damaging the crystal. 3. For SOH28 package, lead-free (Pb-free) lead finish: reflow at peak temperature of 260 °C (the time above 255 °C must not exceed 30 seconds). Caution: Negative undershoots below –0.3 V are not allowed on any pin while in the battery backup mode. Caution: Do NOT wave solder SOIC to avoid damaging SNAPHAT® sockets. Doc ID 2611 Rev 10 17/28

DC and AC parameters M48T35, M48T35Y 5 DC and AC parameters This section summarizes the operating and measurement conditions, as well as the DC and AC characteristics of the device. The parameters in the following DC and AC characteristic tables are derived from tests performed under the measurement conditions listed in the relevant tables. Designers should check that the operating conditions in their projects match the measurement conditions when using the quoted parameters. Table 7. Operating and AC measurement conditions Parameter M48T35 M48T35Y Unit Supply voltage (V ) 4.75 to 5.5 4.5 to 5.5 V CC Ambient operating temperature (T ) 0 to 70 –40 to 85 °C A Load capacitance (C ) 100 100 pF L Input rise and fall times ≤ 5 ≤ 5 ns Input pulse voltages 0 to 3 0 to 3 V Input and output timing ref. voltages 1.5 1.5 V Note: Output Hi-Z is defined as the point where data is no longer driven. Figure 11. AC measurement load circuit 5V 1.9kΩ DEVICE UNDER OUT TEST 1kΩ CL = 100pF or 5pF CL includes JIG capacitance AI01030 Table 8. Capacitance Symbol Parameter(1)(2) Min Max Unit C Input capacitance - 10 pF IN C (3) Output capacitance - 10 pF OUT 1. Effective capacitance measured with power supply at 5 V; sampled only, not 100% tested. 2. At 25 °C, f = 1 MHz. 3. Outputs deselected. 18/28 Doc ID 2611 Rev 10

M48T35, M48T35Y DC and AC parameters Table 9. DC characteristics M48T35 M48T35Y Symbol Parameter Test condition(1) Unit Min Max Min Max I Input leakage current 0 V ≤ V ≤ V ±1 ±1 µA LI IN CC I (2) Output leakage current 0 V ≤ V ≤ V ±1 ±1 µA LO OUT CC I Supply current Outputs open 50 30 mA CC Supply current (standby) I E = V 3 3 mA CC1 TTL IH Supply current (standby) I E = V – 0.2 V 2 2 mA CC2 CMOS CC V Input low voltage –0.3 0.8 –0.3 0.8 V IL V Input high voltage 2.2 V + 0.3 2.2 V + 0.3 V IH CC CC V Output low voltage I = 2.1 mA 0.4 0.4 V OL OL V Output high voltage I = –1 mA 2.4 2.4 V OH OH 1. Valid for ambient operating temperature: T = 0 to 70 or –40 to 85 °C; V = 4.75 to 5.5 V or 4.5 to 5.5 V (except where A CC noted). 2. Outputs deselected. Figure 12. Power down/up mode AC waveforms VCC VPFD (max) VPFD (min) VSO tF tR tFB tRB tPD tDR trec INPUTS RECOGNIZED DON'T CARE RECOGNIZED HIGH-Z OUTPUTS VALID VALID (PER CONTROL INPUT) (PER CONTROL INPUT) AI01168C Doc ID 2611 Rev 10 19/28

DC and AC parameters M48T35, M48T35Y Table 10. Power down/up AC characteristics Symbol Parameter(1) Min Max Unit t E or W at V before power down 0 µs PD IH t (2) V (max) to V (min) V fall time 300 µs F PFD PFD CC M48T35 10 µs t (3) V (min) to V V fall time FB PFD SS CC M48T35Y 10 µs t V (min) to V (max) V rise time 10 µs R PFD PFD CC t V to V (min) V rise time 1 µs RB SS PFD CC t (4) V (max) to inputs recognized 40 200 ms rec PFD 1. Valid for ambient operating temperature: T = 0 to 70 or –40 to 85 °C; V = 4.75 to 5.5 V or 4.5 to 5.5 V (except where A CC noted). 2. V (max) to V (min) fall time of less than t may result in deselection/write protection not occurring until 200 µs after PFD PFD F V passes V (min). CC PFD 3. V (min) to V fall time of less than t may cause corruption of RAM data. PFD SS FB 4. t (min) = 20 ms for industrial temperature grade 6 device. rec Table 11. Power down/up trip points DC characteristics Symbol Parameter(1)(2) Min Typ Max Unit M48T35 4.5 4.6 4.75 V V Power-fail deselect voltage PFD M48T35Y 4.2 4.35 4.5 V M48T35 3.0 V V Battery backup switchover voltage SO M48T35Y 3.0 V Grade 1 10(4) Years t (3)(5) Expected data retention time DR Grade 6 10(5) Years 1. Valid for ambient operating temperature: T = 0 to 70 or –40 to 85 °C; V = 4.75 to 5.5 V or 4.5 to 5.5 V (except where A CC noted). 2. All voltages referenced to V . SS 3. CAPHAT™ and M4T32-BR12SH1 SNAPHAT® only, M4T28-BR12SH1 SNAPHAT® top t = 7 years (typ). DR 4. Using larger M4T32-BR12SH6 SNAPHAT® top (recommended for industrial temperature range - grade 6 device). 5. At 25 °C, V = 0 V. CC 20/28 Doc ID 2611 Rev 10

M48T35, M48T35Y Package mechanical data 6 Package mechanical data In order to meet environmental requirements, ST offers these devices in different grades of ECOPACK® packages, depending on their level of environmental compliance. ECOPACK® specifications, grade definitions and product status are available at: www.st.com. ECOPACK® is an ST trademark. Figure 13. PCDIP28 – 28-pin plastic DIP, battery CAPHAT™, package outline A2 A A1 L C B1 B e1 eA e3 D N E 1 PCDIP Note: Drawing is not to scale. Table 12. PCDIP28 – 28-pin plastic DIP, battery CAPHAT™, package mech. data mm inches Symbol Typ Min Max Typ Min Max A 8.89 9.65 0.350 0.380 A1 0.38 0.76 0.015 0.030 A2 8.38 8.89 0.330 0.350 B 0.38 0.53 0.015 0.021 B1 1.14 1.78 0.045 0.070 C 0.20 0.31 0.008 0.012 D 39.37 39.88 1.550 1.570 E 17.83 18.34 0.702 0.722 e1 2.29 2.79 0.090 0.110 e3 33.02 1.3 eA 15.24 16.00 0.600 0.630 L 3.05 3.81 0.120 0.150 N 28 28 Doc ID 2611 Rev 10 21/28

Package mechanical data M48T35, M48T35Y Figure 14. SOH28 – 28-lead plastic small outline, 4-socket battery SNAPHAT®, package outline A2 A C B e eB CP D N E H A1 α L 1 SOH-A Note: Drawing is not to scale. Table 13. SOH28 – 28-lead plastic SO, 4-socket battery SNAPHAT®, package mechanical data mm inches Symbol Typ Min Max Typ Min Max A 3.05 0.120 A1 0.05 0.36 0.002 0.014 A2 2.34 2.69 0.092 0.106 B 0.36 0.51 0.014 0.020 C 0.15 0.32 0.006 0.012 D 17.71 18.49 0.697 0.728 E 8.23 8.89 0.324 0.350 e 1.27 – – 0.050 – – eB 3.20 3.61 0.126 0.142 H 11.51 12.70 0.453 0.500 L 0.41 1.27 0.016 0.050 a 0° 8° 0° 8° N 28 28 CP 0.10 0.004 22/28 Doc ID 2611 Rev 10

M48T35, M48T35Y Package mechanical data Figure 15. SH – 4-pin SNAPHAT® housing for 48 mAh battery & crystal, package outline A2 A1 A A3 eA B L eB D E SHTK Note: Drawing is not to scale. Table 14. SH – 4-pin SNAPHAT® housing for 48 mAh battery & crystal, package mechanical data mm inches Symbol Typ Min Max Typ Min Max A 9.78 0.385 A1 6.73 7.24 0.265 0.285 A2 6.48 6.99 0.255 0.275 A3 0.38 0.015 B 0.46 0.56 0.018 0.022 D 21.21 21.84 0.835 0.860 E 14.22 14.99 0.560 0.590 eB 3.20 3.61 0.126 0.142 L 2.03 2.29 0.080 0.090 Doc ID 2611 Rev 10 23/28

Package mechanical data M48T35, M48T35Y Figure 16. SH – 4-pin SNAPHAT® housing for 120 mAh battery & crystal, package outline A2 A1 A A3 eA B L eB D E SHTK Note: Drawing is not to scale. Table 15. SH – 4-pin SNAPHAT® housing for 120 mAh battery & crystal, package mechanical data mm inches Symbol Typ Min Max Typ Min Max A 10.54 0.415 A1 8.00 8.51 0.315 0.335 A2 7.24 8.00 0.285 0.315 A3 0.38 0.015 B 0.46 0.56 0.018 0.022 D 21.21 21.84 0.835 0.860 E 17.27 18.03 0.680 0.710 eB 3.20 3.61 0.126 0.142 L 2.03 2.29 0.080 0.090 24/28 Doc ID 2611 Rev 10

M48T35, M48T35Y Part numbering 7 Part numbering Table 16. Ordering information scheme Example: M48T 35 –70 PC 1 E Device type M48T Supply voltage and write protect voltage 35(1) = V = 4.75 to 5.5 V; V = 4.5 to 4.75 V CC PFD 35Y(2) = V = 4.5 to 5.5 V; V = 4.2 to 4.5 V CC PFD Speed –70 = 70 ns Package PC = PCDIP28 MH(3) = SOH28 Temperature range 1 = 0 to 70 °C 6(4) = –40 to 85 °C Shipping method For SOH28: E = ECOPACK® package, tubes F = ECOPACK® package, tape & reel For PCDIP28: blank = ECOPACK® package, tubes 1. The M48T35 part is offered only in the PCDIP28 (i.e. CAPHAT™) package. 2. The M48T35Y is available only in the SOH28 (i.e. SNAPHAT SOIC) package. 3. The SOIC package (SOH28) requires the SNAPHAT® battery package which is ordered separately under the part number “M4TXX-BR12SH” (see Table17 on page25). 4. Temperature grade 6 (–40 to +85 °C) devices are not for new design. Contact ST sales office for availability. Caution: Do not place the SNAPHAT battery package “M4TXX-BR12SH” in conductive foam as it will drain the lithium button-cell battery. For other options, or for more information on any aspect of this device, please contact the ST sales office nearest you. Table 17. SNAPHAT® battery table Part number Description Package ® M4T28-BR12SH Lithium battery (48 mAh) SNAPHAT SH ® M4T32-BR12SH Lithium battery (120 mAh) SNAPHAT SH Doc ID 2611 Rev 10 25/28

Environmental information M48T35, M48T35Y 8 Environmental information Figure 17. Recycling symbols This product contains a non-rechargeable lithium (lithium carbon monofluoride chemistry) button cell battery fully encapsulated in the final product. Recycle or dispose of batteries in accordance with the battery manufacturer's instructions and local/national disposal and recycling regulations. 26/28 Doc ID 2611 Rev 10

M48T35, M48T35Y Revision history 9 Revision history Table 18. Document revision history Date Revision Changes Nov-1999 1 First issue 07-Feb-2000 1.1 t description changed (Table9) DR Reformatted; temp/voltage info. added to tables (Table8, 9, 3, 4, 10, 11); 04-Jun-2001 2 add century bit text 31-Jul-2001 2.1 Formatting changes based on latest document reviews Add PMDIP packaging option, which is “Not for New Design” (NND) 06-Mar-2002 2.2 (Table16) 20-May-2002 2.3 Modify reflow time and temperature footnotes (Table6) 26-Jun-2002 2.4 Add footnote to table (Table11) 31-Mar-2003 3 v2.2 template applied; data retention condition updated (Table11) 10-Dec-2003 4 Reformatted; update DC characteristics (Table9) 31-Mar-2004 5 Reformatted; update Pb-free package information (Table6, 16) 05-Dec-2005 6 Updated template, lead-free text, and remove footnote (Table9, 16) Reformatted; added lead-free second level interconnect information to 01-Aug-2007 7 cover page and Section6: Package mechanical data. Updated Table6; text in Section6: Package mechanical data; added 12-Feb-2009 8 Section8: Environmental information; minor formatting changes. Reformatted document; updated Section4, Table12, 16; removed 08-Sep-2010 9 PMDIP28 package. Updated footnote 1 of Table6: Absolute maximum ratings; updated 07-Jun-2011 10 Section8: Environmental information. Doc ID 2611 Rev 10 27/28

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Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: S TMicroelectronics: M48T35Y-70MH1F M48T35Y-70MH1E M48T35Y-70PC1 M48T35-70PC1 M48T35Y-70MH6F M48T35Y-70MH6E