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MIC2779
Micrel, Inc.
MIC2779
Voltage Monitor with Adjustable Hysteresis
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-pin 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-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% 340k 1%
MIC2779L VDD / R S T LTH HTH GND
IN EN
OUT BYP GND
VOU T 3.0V 4.7F
470pF
VBAT(hi)= 3.6V VBAT(lo)= 3.1V
Cellular Telephone Battery Monitor
IttyBittyTM 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 MIC2779H-2BM5 MIC2779H-1BM5 MIC2779L-2BM5 MIC2779L-1BM5 Marking UPA2 UPA1 UPB2 UPB1 Pb-Free MIC2779H-2YM5 MIC2779H-1YM5 MIC2779L-2YM5 MIC2779L-1YM5 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
LTH GND HTH
3
2
1
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.
2 3
2 3
GND LTH
4
RST
Reset (Output): Push-pull output. This output is asserted and latched when VLTH 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. The polarity of this signal (active-high or low) is deter mined by the part number suffix. See ordering information. Power Supply (Input): Independent supply input for internal circuitry.
5
5
VDD
MIC2779
2
January 2006
MIC2779
Micrel, Inc.
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
Symbol IDD 1.5V VDD 5.5V; TA = +25C, bold values indicate -40C TA +85C; unless noted Parameter Condition Supply Current Input Leakage Current Reference Voltage MIC2779H/L-2 MIC2779H/L-1 tD tRESET VOL Propagation Delay Reset Pulse Width Reset Output Low Voltage VLTH = VREF(max) +100mV to VREF(min) - 100mV /RST asserted or RST not asserted, ISINK = 1.6mA, VDD 1.6V /RST asserted or RST not asserted, ISINK = 100A, VDD 1.2V, /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.
Min
Typ 1 5
Max 2 10
Units A pA nA V V V s
/RST, RST not asserted
ILTH, IHTH VREF
1.240 1.215 1.228 5 140 420 0.3 0.4 0.8VDD 0.8VDD 1.265 1.252
ms V V V V
VOH
Reset Output High Voltage
Timing Diagram
VBATT VHTH VLTH 0V
V/RST
VRST
A
A tRST tRST
VOH VOL
VOH VOL
Propagation delays not shown for clarity. Note A. The MIC2779 ignores very brief transients. See "Applications Information" for details.
January 2006
3
MIC2779
MIC2779
Micrel, Inc.
Functional Diagram
VBATT
VDD
Low-Voltage Detect
VLO
LTH
High-Voltage Detect
One Shot
Delay Line
RQ SQ
/RST*
RST*
VHI
HTH
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
January 2006
MIC2779
Micrel, Inc. 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 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.
Input Transient Response
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 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
R 1 604k 1% R 2 56k 1% R 3 340k 1%
MIC2779 VDD / R S T LTH R ST HTH GND
MAX. TRANSIENT DURATION (s)
140 120 100 80 60 40 20 0 1
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
10
100
1000
RESET COMP. OVERDRIVE, VREF -VLTH (mV)
Figure 2. Input Transient Response
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)
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)
DIMENSIONS: MM (INCH) 0.20 (0.008) 0.09 (0.004)
0.50 (0.020) 0.35 (0.014)
0.60 (0.024) 0.10 (0.004)
5-Pin SOT-23 (M5)
MICREL INC.
TEL
+ 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
2180 FORTUNE DRIVE
SAN JOSE, CA 95131
USA
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. (c) 2000 Micrel, Inc.
MIC2779
6
January 2006

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