MIC2779 Micrel, Inc. MIC2779 Voltage Monitor with Adjustable Hysteresis General Description Features The MIC2779 is a voltage monitor—uniquely designed to detect two separate voltage thresholds—combined with a delay generator and logic. It is designed for monitoring the battery supply of portable digital systems, particularly PDAs, pagers, and cellular telephones. High- and low-voltage thresholds can be adjusted independently, allowing for wide hysteresis. Voltage detection thresholds are accurate to 2%. If the battery voltage falls below the low-voltage threshold, the output /RST or RST is asserted and latched, preventing system operation until the battery is replaced or recharged. Internal logic prevents the output from chattering due to battery recovery or load removal. The output is asserted for 140ms (minimum) when a fresh battery is inserted. For applications requiring open-drain output, see MIC2778/MIC833. The IC’s power supply input is separate from the detector inputs, allowing the MIC2779 to be powered from a downstream supply, such a boost converter. Supply current is extremely low (1µA, typical), making it ideal for portable applications. A high-precision 1% grade is available. The MIC2779 is supplied in Micrel’s IttyBitty™ 5-pin SOT-23-5 package. • Optimized for PDAs, cellular telephones, pagers, and other battery-powered devices • Independently adjustable high- and low-voltage thresholds • Internal logic prevents battery-voltage-fluctuation chatter • High ±2% voltage threshold accuracy; 1% available • Built in 140ms (minimum) delay deglitches output • Extremely low 1µA typical supply current • For applications requiring open-drain output, see MIC2778/MIC833 • Immune to brief power supply transients • 5-pin SOT-23 package Applications • • • • • • PDAs Pagers Cordless phones Consumer electronics Embedded controllers Personal electronics Typical Application MIC5207-3.0BM5 Li-Ion Cell 604k 1% 56k 1% MIC2779L VDD / R S T LTH IN OUT EN GND BYP 470pF VOU T 3.0V 4.7µF HTH GND 340k 1% VBAT(hi)= 3.6V VBAT(lo)= 3.1V Cellular Telephone Battery Monitor IttyBitty™ is a trademark of Micrel, Inc. Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com January 2006 1 MIC2779 MIC2779 Micrel, Inc. Ordering Information Part Number Standard Marking Pb-Free Marking Output Polarity Accuracy Temperature Range Package MIC2779H-2BM5 UPA2 MIC2779H-2YM5 UPA2 Active-High RST 2% –40ºC to +85ºC SOT-23-5 MIC2779H-1BM5 UPA1 MIC2779H-1YM5 UPA1 Active-High RST 1% –40ºC to +85ºC SOT-23-5 MIC2779L-2BM5 UPB2 MIC2779L-2YM5 UPB2 Active-Low /RST 2% –40ºC to +85ºC SOT-23-5 MIC2779L-1BM5 UPB1 MIC2779L-1YM5 UPB1 Active-Low /RST 1% –40ºC to +85ºC SOT-23-5 Pin Configuration LTH GND HTH 3 2 LTH GND HTH 1 3 2 1 4 5 4 5 RST VDD /RST VDD SOT-23-5 (M5) “H” Version SOT-23-5 (M5) “L” Version Pin Description Pin Number MIC2779H Pin Number MIC2779L Pin Name 1 1 HTH High-Voltage Theshold (Input): Analog input to a comparator. When the level on this pin initially rises above VREF, the delay generator cycles and the /RST remains low or RST remains high for a minimum of 140ms. 2 2 GND Ground 3 3 LTH Low-Voltage Threshold (Input): Analog input to a comparator. This is the voltage monitor input assigned to detect a low voltage condition. When the level on this pin falls below VREF, /RST or RST is asserted and the condition is latched until VHTH > VREF. 4 5 MIC2779 Pin Function RST Reset (Output): Push-pull output. This output is asserted and latched when VLTH <VREF, indicating a low voltage condition. This state remains latched until VHTH > VREF. The polarity of this signal (active-high or low) is deter mined by the part number suffix. See ordering information. 4 /RST Reset (Output): Push-pull output. This output is asserted and latched when VLTH <VREF, indicating a low voltage condition. This state remains latched until VHTH > VREF. The polarity of this signal (active-high or low) is deter mined by the part number suffix. See ordering information. 5 VDD Power Supply (Input): Independent supply input for internal circuitry. 2 January 2006 MIC2779 Micrel, Inc. Absolute Maximum Ratings (Note 1) Operating Ratings (Note 2) Supply Voltage (VDD).......................................–0.3V to +7V Input Voltages (VLTH, VHTH, V/RST, VRST)........–0.3V to +7V /RST, RST Output Current (I/RST), (IRST) .................... 20mA Storage Temperature (TS) ........................ –65°C to +150°C ESD Rating, Note 3 ....................................................... 2kV Supply Voltage (VDD) .................................. +1.5V to +5.5V Input Voltages (VLTH, VHTH, V/RST, VRST).....–0.3V to +6.0V Ambient Temperature Range (TA) .............. –40°C to +85°C Package Thermal Resistance................................ 256°C/W Electrical Characteristics 1.5V ≤ VDD ≤ 5.5V; TA = +25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted Symbol Parameter Condition IDD Supply Current /RST, RST not asserted ILTH, IHTH Input Leakage Current VREF Reference Voltage tD Propagation Delay tRESET Max Units 1 2 µA pA 10 nA 1.265 V 1.240 MIC2779H/L-2 1.215 MIC2779H/L-1 1.228 VLTH = VREF(max) +100mV to VREF(min) – 100mV Reset Output Low Voltage VOH Typ 5 Reset Pulse Width VOL Min 140 /RST asserted or RST not asserted, ISINK = 100µA, VDD ≥ 1.2V, /RST not asserted or RST asserted, ISOURCE = 500µA, VDD ≥ 1.6V /RST not asserted or RST asserted, ISOURCE = 50µA, VDD ≥ 1.2V, The device is not guaranteed to function outside its operating rating. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. Note 4. VDD operating range is 1.5V to 5.5V. Output is guaranteed to be held low down to VDD = 1.2V. VLTH VRST VOH VOL V 0.4 V A VHTH V/RST 0.3 V Note 3. VOH VOL ms 0.8VDD Exceeding the absolute maximum rating may damage the device. 0V 420 V Note 2. VBATT V µs 0.8VDD Note 1. Timing Diagram 1.252 5 /RST asserted or RST not asserted, ISINK = 1.6mA, VDD ≥ 1.6V Reset Output High Voltage V A tRST tRST Propagation delays not shown for clarity. Note A. January 2006 The MIC2779 ignores very brief transients. See “Applications Information” for details. 3 MIC2779 MIC2779 Micrel, Inc. Functional Diagram VDD VBATT VLO VHI Low-Voltage Detect LTH One Shot High-Voltage Detect HTH Delay Line R Q /RST* S Q RST* 1.24V Bandgap Reference MIC2779 GND * Pinout and polarity vary by device type. See ordering information table. Functional Description Trip Points Battery voltage is monitored by a comparator via a voltage divider network. The divided voltage is compared to an internal reference voltage. When the voltage at the LTH input pin drops below the internal reference voltage, the output is asserted. At this point, the voltage at HTH is assumed to be below the reference voltage. Delay At power-on or when the battery is replaced or recharged, and the voltage at HTH exceeds the reference voltage, the output is deasserted after a minimum delay of 140ms. The MIC2779 monitors the voltage of a battery and detects when it is discharged below a programmed level. Upon being replaced, or being recharged above a second higher programmed trip point, the output remains low (MIC2779L) or high (MIC2779H) for a minimum of 140ms and then sends a reset signal to a microprocessor or other downstream component. See “Timing Diagram.” /RST, RST Low Output The output is a push-pull logic signal which is asserted when the MIC2779 detects a low input voltage. The MIC2779L’s /RST output is active-low; the MIC2779H’s RST output is active-high. MIC2779 4 January 2006 MIC2779 Micrel, Inc. Applications Information Once R3 is determined, the equation for VBAT(lo) can be used to determine R2. A single lithium-ion cell should not be discharged below 2.5V. Many applications limit the drain to 3.1V. Using 3.1V for the VBAT(lo) threshold allows calculation of the two remaining resistor values. 1MΩ VBAT(lo) = 3.1V = 1.24 R2 + 344k Programming the Thresholds The low-voltage threshold is calculated using: R1 + R2 + R3 VBAT(lo) = VREF R2 + R3 The high-voltage threshold is calculated using: R1 + R2 + R3 VBAT(hi) = VREF R3 R2 = 56k Ω R1 = 1MΩ − R2 − R3 R1 = 600k Ω where, for both equations: VREF = 1.240V The accuracy of the resistors can be chosen based upon the accuracy required by the system. Input Transients The MIC2779 is inherently immune to very short negativegoing “glitches.” Very brief transients may exceed the VBAT(lo) threshold without tripping the output. As shown in Figure 2, the narrower the transient, the deeper the threshold overdrive that will be ignored by the MIC2779. The graph represents the typical allowable transient duration for a given amount of threshold overdrive that will not generate a reset. 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 = RTOTAL. A value such as 1MΩ for RTOTAL is a reasonable value because it draws minimum battery current but has no measurable effect on 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 VBAT to ground is 3MΩ. R 1 604k 1% R 2 56k 1% MAX. TRANSIENT DURATION (µs) VBATT MIC2779 VDD / R S T LTH R ST HTH GND R 3 340k 1% Figure 1. Example Circuit Once the desired trip points are determined, set the VBAT(hi) threshold first. For example, use a total of 1MΩ = R1 + R2 + R3. For a typical single-cell lithium ion battery, 3.6V is a good “high threshold” because at 3.6V the battery is moderately charged. Solving for R3: 1MΩ VBAT(hi) = 1.24 R3 Input Transient Response 140 120 100 80 60 40 20 0 1 10 100 1000 RESET COMP. OVERDRIVE, VREF –VLTH (mV) Figure 2. Input Transient Response R3 = 344kΩ January 2006 5 MIC2779 MIC2779 Micrel, Inc. Package Information 1.90 (0.075) REF 0.95 (0.037) REF 1.75 (0.069) 3.00 (0.118) 1.50 (0.059) 2.60 (0.102) DIMENSIONS: MM (INCH) 1.30 (0.051) 0.90 (0.035) 3.02 (0.119) 2.80 (0.110) 0.20 (0.008) 0.09 (0.004) 10° 0° 0.50 (0.020) 0.35 (0.014) 0.15 (0.006) 0.00 (0.000) 0.60 (0.024) 0.10 (0.004) 5-Pin SOT-23 (M5) MICREL INC. TEL 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. 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, Inc. MIC2779 6 January 2006