MIC2755 Battery Operated Supervisor General Description Features The MIC2755 is composed of multiple comparators, a • Optimized for PDAs, pagers, and other handheld reset pulse generator, and logic. It is designed for devices monitoring the battery supply of portable digital systems, • Detects multiple battery states: including PDAs and pagers. − Battery OK The MIC2755 can detect three different battery states: − Low battery battery OK, low battery, and dead battery. The reset − Dead battery (/RST) output is asserted for at least 700ms when a fresh battery is inserted. The non-maskable interrupt output • Adjustable voltage thresholds (/NMI) is asserted when the battery voltage is below the • High accuracy ±2% voltage thresholds NTH threshold, indicating that high-power system • Reset generation at power-on (700ms min.) operations should not occur. If and when battery voltage • Debounced manual reset function falls below the power-off threshold (PTH), the reset output is asserted and latched, inhibiting system operation until • Internal logic prevents chatter if battery voltage the battery is replaced or recharged. fluctuates All three voltage thresholds are set using external • Extremely low 2μA typical supply current resistors. A manual reset function can be implemented by • I/Os can be pulled above VDD (7V absolute maximum) connecting a switch directly to the power on reset/manual • Immune to brief power supply transients reset [RTH(/MR)] input. Internal circuitry detects switch • Low cost activation and generates a minimum 175ms debounced reset signal. The MIC2755’s power supply input is • 8-pin MSOP separate from the detector inputs to allow it to be powered from a down-stream voltage, such as the output of a boost converter. Inputs and outputs can be pulled above VDD (up to 7V absolute maximum) without adverse effects or excessive current draw. Supply current is typically a low 2μA. Hysteresis is included on all voltage detectors to prevent chattering due to noise. The MIC2755 is available in the tiny 8-pin micro- small-outline package. Datasheets and support documentation are available on Micrel’s web site at: www.micrel.com. Typical Application Supervised Boost Converter and Microcontroller or Microprocessor Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com May 21, 2015 Revision 2.0

Micrel, Inc. MIC2755 Ordering Information Part Number Junction Temperature Range Lead Finish Package MIC2755YMM –40°C to +85°C Pb-Free 8-Pin MSOP Pin Configuration 8-Pin MSOP (MM) (Top View) Pin Description Pin Number Pin Name Pin Function Power-On Reset Threshold (Analog Input). Comparator input assigned to battery-OK condition 1 RTH(/MR) detection. When the level on this pin first exceeds V , the reset generator cycles. The /RST REF output is held low for a minimum of 700ms and the /POF threshold output is de-asserted. Non-maskable Interrupt Threshold (Analog Input). Voltage monitor input assigned to “low battery” 2 NTH condition detection. When the level on this pin falls below V , the /NMI output is asserted. REF Power-Off Threshold (Analog Input). Voltage monitor input assigned to “dead battery” condition 3 PTH detection. When the level on this pin falls below VREF, the /RST and /POF outputs are asserted. The condition is latched until a reset cycle occurs (V > V ). RTH REF 4 GND Ground. Power and signal return for all IC functions. Power-Off (Output). Active-low, open-drain output. Asserted and latched when V < V , which 5 /POF PTH REF is a “dead battery” condition. Non-maskable Interrupt (Output). Active-low, open-drain output. Asserted when V < V , PTH REF 6 /NMI which is a “low battery” condition. This indicates high-power system operation should not be allowed. Reset (Output). Active-low, open-drain output. Asserted for a minimum of 700ms at power-on or 7 /RST anytime V drops below V . Also asserted for 175ms minimum when RTH (/MR) is externally PTH REF pulled low (manual reset). 8 VDD Analog Input. Power supply input. May 21, 2015 2 Revision 2.0

Micrel, Inc. MIC2755 (1) (2) Absolute Maximum Ratings Operating Ratings Supply Voltage (V ) ....................................... –0.3V to +7V Supply Voltage (V ) .................................... +1.5V to +5.5V DD DD Input Voltage (V , V V ) ....................... –0.3V to +7V Input Voltage (V , V V ) ....................... –0.3V to +6V RTH NTH, PTH RTH NTH, PTH Output Voltage (V , V V ) .................. –0.3V to +7V Output Voltage (V , V V ) .................. –0.3V to +6V /RST /NMI, /POF /RST /NMI, /POF /RST Output Current (I ) ......................................... 20mA Ambient Temperature (T ) .......................... –40°C to +85°C /RST A Storage Temperature (T ) ........................... –65°C to 150°C Package Thermal Resistance S ESD Rating(3) .................................................................. 2kV 1-layer PCB (θ ) ............................................. 206°C/W JA 4-layer PCB (θ ) ............................................. 113°C/W JA (4) Electrical Characteristics VIN = 3.3; TA = 25°C, bold values indicate –40°C≤ TA ≤ +85°C, unless noted. Symbol Parameter Condition Min. Typ. Max. Units outputs open, VRTH, VNTH, VPTH > 1.24V 2.0 4.0 µA I Operating Supply Current DD outputs open, VRTH, VNTH, VPTH < 1.24V 1.7 µA IRTH(/MR), INTH, 5 pA I , I , I , Leakage Current PTH /RST /NMI 10 nA I /POF VREF1 Threshold Voltage for RTH(/MR) and PTH inputs 1.215 1.240 1.265 V VREF2 Threshold Voltage For NTH inputs 1.215 1.240 1.265 V Hysteresis Voltage on NTH V 20 mV HYST Comparator Reset Output (/RST) t/RST Reset Pulse Width 700 1200 ms t/MR Manual Reset Pulse Width 175 300 ms /RST Output Voltage Low, /RST asserted, ISINK = 1.6mA, VDD ≥ 1.6V 0.3 V V /RST Note 5 /RST asserted, ISINK = 100µA, VDD ≥ 1.2V 0.4 V Reset Input [RTH(/MR)] V/MRTV Manual Reset Trip Voltage 275 310 345 mV tDBNC Debounce Time V/MRT(min) < VRTH < V/MRTV(max), Note 6 22 38 ms from (V < V 100mV) to RST t Propagation Delay /MR RTH(/MR)(min)– 9 µs PROP Asserted Non–maskable Interrupt Output (/NMI) t Propagation Delay (V +100mV) < V < (V – 100mV) 9 µs PROP REF(max) NTH REF(min) /NMI asserted, ISINK = 1.6mA, VDD ≥ 1.6V 0.3 V V /NMI Output Voltage Low /NMI /NMI asserted, ISINK = 100µA, VDD ≥ 1.2V 0.4 V Power–Off Output (/POF) t Propagation Delay (V +100mV) < V < (V – 100mV) 9 µs PROP REF(max) PTH REF(min) /POF asserted, ISINK = 1.6mA, VDD ≥ 1.6V 0.3 V V /POF Output Voltage Low /POF /POF asserted, ISINK = 100µA, VDD ≥ 1.2V 0.4 V Notes: 1. Exceeding the absolute maximum ratings may damage the device. 2. The device is not guaranteed to function outside its operating ratings. 3. Devices are ESD sensitive. Handling precautions are recommended. Human body model, 100pF in series with 1.5kΩ. 4. Specification for packaged product only. 5. V operating range is 1.5V to 5.5V. Output is guaranteed to be held low down to V = 1.2V. DD DD 6. . These relationships are guaranteed by design. 𝑡𝑡/𝑅𝑅𝑅𝑅𝑅𝑅 𝑡𝑡/𝑀𝑀𝑅𝑅 𝑡𝑡𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷= 32 = 8 May 21, 2015 3 Revision 2.0

Micrel, Inc. MIC2755 Timing Diagram Propagation delays not shown for clarity. The MIC2755 ignores very brief transients. See “Application Information” for details. Block Diagram May 21, 2015 4 Revision 2.0

Micrel, Inc. MIC2755 Functional Description Power-Off Output The /POF output and the /RST output are asserted and Typically the MIC2755 is used to monitor the battery latched when V < V , indicating a “dead battery.” The supply of intelligent circuits such as microcontrollers and PTH REF system is held in reset until the battery is replaced or microprocessors. By connecting the reset output of a recharged and a power-on reset cycle occurs; that is, V MIC2755 to the reset input of a μC or μP, the processor RTH > V . The /POF output may be used to control a linear will be properly reset at power-on and during power-down REF1 or switching regulator, shutting down the regulator when and low battery conditions. The /NMI output provides low- the battery reaches it end-of-life voltage. battery warnings to the system. In addition, a system whose battery voltage declines below the PTH threshold is The /POF pin is an active-low, open-drain digital output held in reset to prevent spurious operation. Thus the and may be wire-ORed with other open-drain logic signals. MIC2755 effectively detects three battery states: “battery Most applications will require a pull-up resistor on this OK,” “low battery,” and “dead battery.” output. The /POF pin may be pulled up to any voltage not exceeding V even if this voltage is higher than VDD /POF(max) Reset Output (see “Electrical Characteristics”). The /RST is an active-low, open-drain digital output. This output is asserted for a minimum of 700ms at power-on Power-On Reset and for a minimum of 175ms when RTH(/MR) is externally The RTH(/MR) and PTH inputs work together to provide pulled low, indicating that a manual reset should be predictable battery monitoring with user-programmable initiated. The /RST pin is an active-low, open-drain digital hysteresis and without chatter. The /RST output is output and may be wire-ORed with other open-drain logic asserted for a minimum of 700ms at power-on. Power-on signals. Most applications will require a pull-up resistor on is determined by RTH(/MR) exceeding V . Once this REF1 this pin. The /RST pin may be pulled up to any voltage not event has occurred, the internal logic ignores further exceeding V even if this voltage is higher than VDD transitions on the RTH(/MR) input, instead monitoring for a /RST(max) (see “Electrical Characteristics”). low voltage on PTH or the manual reset condition. If V PTH drops below V , the /POF and /RST outputs are REF1 Non-maskable Interrupt Output asserted and latched, holding the system in its reset state. The /NMI pin is the output of a comparator that constantly compares the level on the NTH pin with the internal Manual Reset voltage reference, V . This output is asserted when An internal circuit monitors RTH(/MR), the comparing pin it REF2 V < V , indicating high-power system operation to an internal 310mV reference, V . When RTH(/MR) is NTH REF2 /MRTV should not occur; that is, the battery is low but not dead. pulled below V , and V is still above V , the /MRTV PTH REF1 Effectively, this function is an uncommitted comparator internal circuitry initiates a manual reset cycle and asserts with its inverting input connected to the internal reference, /RST for at least 175ms. A momentary push-button switch V , its non-inverting input connected to NTH, and its is typically connected such that RTH(/MR) is forced to REF2 output on /NMI. This comparator does not affect any other ground when the switch contacts close. This switch is MIC2755 functions and may be used independently. internally debounced. Each closure of the switch longer than t results in a single output pulse of no less than The /NMI pin is an active-low, open-drain digital output and DBNC 175ms and no more than 300ms being generated. (The may be wire-ORed with other open-drain logic signals. manual reset pulse is derived from the same oscillator and Most applications will require a pull-up resistor on this pin. counter as t . The length of t is always equal to one The /NMI pin may be pulled up to any voltage not /RST /MR fourth of t .) This prevents a user who may hold the exceeding V even if this voltage is higher than VDD /RST /NMI(max) switch closed from keeping the system in reset for an (see “Electrical Characteristics”). extended period of time. May 21, 2015 5 Revision 2.0

Micrel, Inc. MIC2755 Applications Information For a typical single-cell lithium ion battery, 3.6V is a reasonable “OK threshold” because at 3.6V the battery is Output moderately charged. Solving for R4: Since the MIC2755 outputs are open-drain MOSFETs, V = 3.6V = 1.24V most applications will require pull-up resistors. The value BAT(OK) 1𝑀𝑀Ω of the resistors should not be too large or leakage effects R4 = 344KΩ � 𝑅𝑅4 � may dominate. To determine the resistor values for V threshold, set Programming Thresholds BAT(low) R4 = 344kΩ and solve for R3. There are separate resistive-divider configurations for circuits that require or do not require manual reset V = 3.1V = 1.24V BAT(LOW) capability. 1𝑀𝑀Ω R4 = 56KΩ �𝑅𝑅3+ 𝑅𝑅4� Configuration Without Manual Reset Once R3 and R4 are determined, the equation for See Figure 1. The battery-OK threshold is calculated using: VBAT(DEAD) can be used to determine R2. A single lithium- ion cell should not be discharged below 2.5V. Many applications limit the drain to 2.9V. Using 2.9V for the VBAT(DEAD) threshold allows calculating the following resistor 𝑅𝑅1+𝑅𝑅2+𝑅𝑅3+𝑅𝑅4 The low-batte𝑉𝑉r𝐷𝐷y𝐵𝐵 𝐵𝐵th(𝑂𝑂r𝑂𝑂e)sh=o l𝑉𝑉d𝑅𝑅 i𝑅𝑅s𝑅𝑅 c �alculated using: � values. 𝑅𝑅4 V = 2.9V = 1.24V BAT(DEAD) 1𝑀𝑀Ω 𝑅𝑅1+𝑅𝑅2+𝑅𝑅3+𝑅𝑅4 R2 = 27.4k �𝑅𝑅2+55.6𝑘𝑘Ω+ 344𝑘𝑘Ω� The dead-b𝑉𝑉a𝐷𝐷𝐵𝐵tt𝐵𝐵e(r𝑙𝑙𝑙𝑙y𝑙𝑙 t)h=re s𝑉𝑉h𝑟𝑟o𝑟𝑟𝑟𝑟ld �is calculated using: � 𝑅𝑅3+𝑅𝑅4 R1 = 1MΩ – R2 – R3 – R4 = 572k Configuration with Manual Reset 𝑅𝑅1+𝑅𝑅2+𝑅𝑅3+𝑅𝑅4 where, for𝑉𝑉 a𝐷𝐷l𝐵𝐵l 𝐵𝐵e(𝐷𝐷q𝑅𝑅u𝐵𝐵a𝐷𝐷t)io=ns 𝑉𝑉: 𝑟𝑟𝑟𝑟𝑟𝑟 � � To use manual reset, the MIC2755 requires a separate 𝑅𝑅3+𝑅𝑅4 resistor ladder for the switch and fresh-battery threshold. V = 1.24V The remaining two thresholds are set by the three-resistor REF ladder. See Figure 2. In order to provide the additional criteria needed to solve for the resistor values, the resistors can be selected such that they have a given total value, that is, R1 + R2 + R3 + R4 = R . A value such as 1MΩ for R is a reasonable total total value because it draws minimum battery current per resistor ladder but has no significant effect on system accuracy. When working with large resistors, a small amount of leakage current can cause voltage offsets that degrade system accuracy. The maximum recommended total resistance from V to ground is 3MΩ. BAT Figure 2. Example Circuits with Manual Reset 𝑅𝑅6+𝑅𝑅7 𝑉𝑉𝐷𝐷𝐵𝐵𝐵𝐵(𝑂𝑂𝑂𝑂) = 𝑉𝑉𝑅𝑅𝑅𝑅𝑅𝑅 � � 𝑅𝑅7 𝑅𝑅8+𝑅𝑅9+𝑅𝑅10 𝑉𝑉𝐷𝐷𝐵𝐵𝐵𝐵(𝐿𝐿𝑂𝑂𝐿𝐿) = 𝑉𝑉𝑅𝑅𝑅𝑅𝑅𝑅 � � 𝑅𝑅10 𝑅𝑅8+𝑅𝑅9+𝑅𝑅10 where, for a𝑉𝑉ll𝐷𝐷 e𝐵𝐵q𝐵𝐵(u𝐷𝐷a𝑅𝑅t𝐵𝐵io𝐷𝐷)ns=: 𝑉𝑉𝑅𝑅𝑅𝑅𝑅𝑅 � � 𝑅𝑅9+𝑅𝑅10 VREF = 1.24V Figure 1. Example Circuit without Manual Reset Once the desired trip points are determined, set the V threshold first. BAT(OK) May 21, 2015 6 Revision 2.0

Micrel, Inc. MIC2755 Once the desired trip points are determined, set R6 + R7 capability can be added as discussed in the Manual Reset =1MΩ and solve for R7. and Configuration with Manual Reset sections. This same configuration can be used to detect the V = 3.6V = 1.24V BAT(fresh) 1𝑀𝑀Ω presence of an auxiliary power source such as an ac R7 = 344kΩ � R7 � adapter instead of monitoring a battery. R4 and R5 would be selected such that the /NMI output is deasserted when R6 = 1MΩ – 344k = 656kΩ the proper input voltage is applied. The remaining resistor values are solved in a similar Voltage Supervisor with Power Fail Warning manner as the above. Figure 6 illustrates the MIC2755 being used as a voltage 1MΩ = R8 + R9 + R10 supervisor and a power-fail detector in a 3.3V system. The primary voltage monitor is configured as a voltage V =3.1V = 1.24V BAT(low) supervisor with a nominal trip point of 3.034V and 33mV of 1𝑀𝑀Ω hysteresis as set by R1, R2, and R3. The NMI comparator R10 = 400kΩ �𝑅𝑅10� is used to detect an impending power failure such as a 1MΩ = R10 + R11 low-battery condition or ac power outage. The /NMI output will be asserted if the input voltage to the LDO regulator VBAT(dead) =2.9V = 1.24V falls below 3.55V. (The MIC5245 has a specified maximum 1𝑀𝑀Ω dropout of 250mV at 150mA output current. If the input R9 = 27kΩ �𝑅𝑅9+400𝑘𝑘Ω� voltage falls below 3.55V, the output may droop.) By R8 = 1MΩ – R9 – R10 – = 573kΩ monitoring the input of the LDO regulator, the system receives the earliest warning of an impending power loss. The accuracy of the resistors can be chosen based upon Manual reset capability can be added as discussed in the the accuracy required by the system. Manual Reset and Configuration with Manual Reset Input Transients sections. The MIC2755 is inherently immune to very short negative going “glitches.” Very brief transients may cross the V or V thresholds without tripping the BAT(LOW) BAT(dead) output(s). As shown in Figure 3 and Figure 4, the narrower the transient, the deeper the threshold overdrive that will be ignored by the MIC2755. The graph represents the typical allowable transient duration for a given amount of threshold overdrive that will not cause the corresponding output to change state. Alternate Configurations The MIC2755 can be used in a variety of ways. It is especially flexible due to the fact that the NMI comparator Figure 3. Input Transient Response is completely independent. There are other useful configurations beside a three-state battery monitor. The NMI comparator can be used to provide power-fail indication (PFI/PFI), monitor an auxiliary battery (LBI/LBO), or detect the presence of an AC adapter. Voltage Supervisor and Backup Battery Monitor Figure 5 illustrates the MIC2755 being used as a voltage supervisor and a battery monitor in a 3.3V system with a Lithium coin-cell backup. The primary voltage monitor is configured as a voltage supervisor with a nominal trip point of 3.034V and 33mV of hysteresis as set by R1, R2, and R3. The NMI comparator is used to detect a low-battery condition so the system is aware that the backup battery is discharged. In this example, the /NMI output will be asserted if battery voltage falls below 2.2V. Manual reset Figure 4. Input Transient Response May 21, 2015 7 Revision 2.0

Micrel, Inc. MIC2755 Supervised Boost Converter and Microcontroller or Microprocessor In Figure 7 and Figure 8, the MIC2755 is used to monitor the battery and the MIC3172 is used to maintain the output voltage at 3.3V by boosting the input voltage. When the Li- ion battery voltage drops to 3.1V, the MIC2755 alerts the microcontroller or the microprocessor. When the battery voltage drops to 2.9V, the MIC2755 turns off the MIC3172. May 21, 2015 8 Revision 2.0

Micrel, Inc. MIC2755 Figure 5. Voltage Supervisor and Backup Battery Monitor Figure 6. Voltage Supervisor with Power Fail Warning May 21, 2015 9 Revision 2.0

Micrel, Inc. MIC2755 Typical Application Schematic Typical Application without Manual Reset Typical Application with Manual Reset May 21, 2015 10 Revision 2.0

Micrel, Inc. MIC2755 (7) Package Information and Recommended Landing Pattern 8-Pin MSOP (MM) Note: 7. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com. May 21, 2015 11 Revision 2.0

Micrel, Inc. MIC2755 MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com Micrel, Inc. is a leading global manufacturer of IC solutions for the worldwide high performance linear and power, LAN, and timing & communications markets. The Company’s products include advanced mixed-signal, analog & power semiconductors; high-performance communication, clock management, MEMs-based clock oscillators & crystal-less clock generators, Ethernet switches, and physical layer transceiver ICs. Company customers include leading manufacturers of enterprise, consumer, industrial, mobile, telecommunications, automotive, and computer products. Corporation headquarters and state-of-the-art wafer fabrication facilities are located in San Jose, CA, with regional sales and support offices and advanced technology design centers situated throughout the Americas, Europe, and Asia. Additionally, the Company maintains an extensive network of distributors and reps worldwide. Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this datasheet. This information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright, or other intellectual property right. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2000 Micrel, Incorporated. May 21, 2015 12 Revision 2.0