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| MIC2779 Micrel MIC2779 Voltage Monitor with Adjustable Hysteresis Preliminary Information General Description 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 (1A, typical), making it ideal for portable applications. A high-precision 1% grade is available. The MIC2779 is supplied in Micrel's IttyBittyTM 5-lead SOT-23-5 package. Features * 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 1A typical supply current * For applications requiring open-drain output, see MIC2778/MIC833 * Immune to brief power supply transients * 5-lead SOT-23 package Applications * * * * * * PDAs Pagers Cordless phones Consumer electronics Embedded controllers Personal electronics Typical Application MIC5207-3.0BM5 IN Li-Ion Cell 604k 1% 56k 1% 340k 1% MIC2779L VDD LTH HTH GND /RST EN OUT BYP GND 470pF VOUT 3.0V 4.7F VBAT(hi) = 3.6V VBAT(lo) = 3.1V Cellular Telephone Battery Monitor IttyBittyTM is a trademark of Micrel, Inc. Micrel, Inc. * 1849 Fortune Drive * San Jose, CA 95131 * USA * tel + 1 (408) 944-0800 * fax + 1 (408) 944-0970 * http://www.micrel.com June 2000 1 MIC2779 MIC2779 Micrel Ordering Information Part Number MIC2779H-2BM5 MIC2779H-1BM5 MIC2779L-2BM5 MIC2779L-1BM5 Marking UPA2 UPA1 UPB2 UPB1 Output Polarity Active-High RST Active-High RST Active-Low /RST Active-Low /RST Accuracy 2% 1% 2% 1% Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C Package SOT-23-5 SOT-23-5 SOT-23-5 SOT-23-5 Pin Configuration LTH GND HTH 3 2 1 LTH GND HTH 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 1 Pin Number MIC2779L 1 Pin Name HTH Pin Function 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. Ground 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. Reset (Output): Push-pull output. This output is asserted and latched when VLTH 2 3 2 3 GND LTH 4 RST 4 /RST 5 5 VDD MIC2779 2 June 2000 MIC2779 Micrel Absolute Maximum Ratings (Note 1) 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) ....................... -65C to +150C ESD Rating, Note 3 ...................................................... 2kV Operating Ratings (Note 2) Supply Voltage (VDD) .................................. +1.5V to +5.5V Input Voltages (VLTH, VHTH, V/RST, VRST) .. -0.3V to +6.0V Ambient Temperature Range (TA) ............. -40C to +85C Package Thermal Resistance ............................... 256C/W Electrical Characteristics 1.5V VDD 5.5V; TA = +25C, bold values indicate -40C TA +85C; unless noted Symbol IDD ILTH, IHTH VREF Parameter Supply Current Input Leakage Current Condition /RST, RST not asserted Min Typ 1 5 10 Reference Voltage MIC2779H/L-2 MIC2779H/L-1 tD tRESET VOL Propagation Delay Reset Pulse Width Reset Output Low Voltage /RST asserted or RST not asserted, ISINK = 1.6mA, VDD 1.6V /RST asserted or RST not asserted, ISINK = 100A, VDD 1.2V, VOH Reset Output High Voltage /RST not asserted or RST asserted, ISOURCE = 500A, VDD 1.6V /RST not asserted or RST asserted, ISOURCE = 50A, VDD 1.2V, Note 1. Note 2. Note 3. Note 4. Exceeding the absolute maximum rating may damage the device. 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. VDD operating range is 1.5V to 5.5V. Output is guaranteed to be held low down to VDD = 1.2V. Max 2 Units A pA nA V 1.240 1.215 1.228 5 140 420 0.3 0.4 0.8VDD 0.8VDD 1.265 1.252 V V s ms V V V V VLTH = VREF(max) +100mV to VREF(min) - 100mV Timing Diagram A VHTH VBATT VLTH A 0V V/RST VOH VOL VOH VOL tRST tRST VRST Propagation delays not shown for clarity. Note A. The MIC2779 ignores very brief transients. See "Applications Information" for details. June 2000 3 MIC2779 MIC2779 Micrel Functional Diagram VDD VBATT Low-Voltage Detect LTH RQ HTH VHI High-Voltage Detect Delay Line One Shot SQ RST* /RST* VLO 1.24V Bandgap Reference MIC2779 GND * Pinout and polarity vary by device type. See ordering information table. Functional Description 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. 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. MIC2779 4 June 2000 MIC2779 Micrel 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. 1M VBAT(lo) = 3.1V = 1.24 R2 + 344k Applications Information 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 where, for both equations: VREF = 1.240V R2 = 56k R1 = 1M - R2 - R3 R1 = 600k 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. MAX. TRANSIENT DURATION (s) 140 120 100 80 60 40 20 0 1 10 100 1000 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 1M 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 3M. VBATT Input Transient Response R1 604k 1% 56k 1% 340k 1% MIC2779 VDD LTH HTH /RST RST GND R2 R3 Figure 1. Example Circuit Once the desired trip points are determined, set the VBAT(hi) threshold first. For example, use a total of 1M = 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: 1M VBAT(hi) = 1.24 R3 R3 = 344k RESET COMP. OVERDRIVE, VREF-VLTH (mV) Figure 2. Input Transient Response June 2000 5 MIC2779 MIC2779 Micrel Package Information 1.90 (0.075) REF 0.95 (0.037) REF 1.75 (0.069) 1.50 (0.059) 3.00 (0.118) 2.60 (0.102) DIMENSIONS: MM (INCH) 3.02 (0.119) 2.80 (0.110) 1.30 (0.051) 0.90 (0.035) 10 0 0.15 (0.006) 0.00 (0.000) 0.20 (0.008) 0.09 (0.004) 0.50 (0.020) 0.35 (0.014) 0.60 (0.024) 0.10 (0.004) SOT-23-5 (M5) MIC2779 6 June 2000 MIC2779 Micrel June 2000 7 MIC2779 MIC2779 Micrel MICREL INC. TEL 1849 FORTUNE DRIVE SAN JOSE, CA 95131 FAX USA + 1 (408) 944-0800 + 1 (408) 944-0970 WEB http://www.micrel.com This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc. (c) 2000 Micrel Incorporated MIC2779 8 June 2000 |
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