Datasheet MIC2779H-2BM5, MIC2779L-1BM5, MIC2779L-2BM5, MIC2779H-1BM5 Datasheet (MICREL)

MIC2779 Micrel

V

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 (1µA, typical), making it ideal for portable
applications.

A high-precision 1% grade is available. The MIC2779 is
supplied in Micrel’s IttyBitty™ 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 1µA 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

T ypical Application

MIC5207-3.0BM5

OUT

BYP

GND

470pF

Li-Ion

Cell

604k
1%

56k
1%

340k
1%

MIC2779L

VDD
LTH
HTH

V

= 3.6V

BAT(hi)

= 3.1V

V

BAT(lo)

/RST

GND

IN

EN

Cellular Telephone Battery Monitor

IttyBitty™ is a trademark of Micrel, Inc.

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 [phone] • fax + 1 [phone] • http://www.micrel.com

June 2000 1 MIC2779

OUT

3.0V

4.7µF

MIC2779 Micrel

Ordering Information

Part Number Marking Output Polarity Accuracy Temperature Range Package

MIC2779H-2BM5 UPA2 Active-High RST 2% –40°C to +85°C SOT-23-5
MIC2779H-1BM5 UPA1 Active-High RST 1% –40°C to +85°C SOT-23-5
MIC2779L-2BM5 UPB2 Active-Low /RST 2% –40°C to +85°C SOT-23-5
MIC2779L-1BM5 UPB1 Active-Low /RST 1% –40°C to +85°C SOT-23-5

Pin Configuration

GND

2

HTH

13

LTH

45

VDDRST

SOT-23-5 (M5)

“H” Version

LTH

45

SOT-23-5 (M5)

“L” Version

GND

2

HTH

13

VDD/RST

Pin Description

Pin Number Pin Number Pin Name Pin Function

MIC2779H MIC2779L

1 1 HTH High-Voltage Theshold (Input): Analog input to a comparator. When the

level on this pin initially rises above V

/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 V

is latched until V

HTH

> V

REF

, /RST or RST is asserted and the condition

REF

.

4 RST Reset (Output): Push-pull output. This output is asserted and latched when

V

<V

LTH

until V

mined by the part number suffix. See ordering information.

, indicating a low voltage condition. This state remains latched

REF

HTH

> V

. The polarity of this signal (active-high or low) is deter

REF

4 /RST Reset (Output): Push-pull output. This output is asserted and latched when

<V

V

LTH

until V

, indicating a low voltage condition. This state remains latched

REF

HTH

> V

. The polarity of this signal (active-high or low) is deter

REF

mined by the part number suffix. See ordering information.
5 5 VDD Power Supply (Input): Independent supply input for internal circuitry.

, the delay generator cycles and the

REF

MIC2779 2 June 2000

MIC2779 Micrel

Absolute Maximum Ratings (Note 1)

Supply Voltage (V
Input Voltages (V
/RST, RST Output Current (I

Storage Temperature (TS) .......................–65°C to +150°C

) ..................................... –0.3V to +7V

DD

, V

LTH

HTH

, V

/RST

/RST

, V

), (I

) ..... –0.3V to +7V

RST

)...................20mA

RST

Operating Ratings (Note 2)

Supply Voltage (V
Input Voltages (V
Ambient Temperature Range (T

Package Thermal Resistance ...............................256°C/W

) .................................. +1.5V to +5.5V

DD

, V

LTH

HTH

, V

, V

/RST

) ............. –40°C to +85°C

A

)..–0.3V to +6.0V

RST

ESD Rating, Note 3 ......................................................2kV

Electrical Characteristics

1.5V ≤ VDD ≤ 5.5V; TA = +25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted
Symbol Parameter Condition Min Typ Max Units

I

DD

I

LTH, IHTH

V

REF

t

D

t

RESET

V

OL

V

OH

Note 1. Exceeding the absolute maximum rating may damage the device.
Note 2. The device is not guaranteed to function outside its operating rating.
Note 3. 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.

Supply Current /RST, RST not asserted 1 2 µA
Input Leakage Current 5pA

10 nA

Reference Voltage 1.240 V

MIC2779H/L-2 1.215 1.265 V
MIC2779H/L-1 1.228 1.252 V

Propagation Delay V

LTH

V

REF(min)

= V

REF(max)

– 100mV

+100mV to 5 µs

Reset Pulse Width 140 420 ms
Reset Output Low Voltage /RST asserted or RST not asserted,

I

= 1.6mA, VDD ≥ 1.6V 0.3 V

SINK

/RST asserted or RST not asserted,
I

= 100µA, VDD ≥ 1.2V, 0.4 V

SINK

Reset Output High Voltage /RST not asserted or RST asserted,

I

SOURCE

= 500µA, VDD ≥ 1.6V 0.8V

DD

V

/RST not asserted or RST asserted,
I

SOURCE

= 50µA, VDD ≥ 1.2V, 0.8V

DD

V

Timing Diagram

V

BATT

V

HTH

LTH

V

A

0V

V

/RST

RST

OH

V

OL

V

OH

V

OL

Propagation delays not shown for clarity.

Note A. The MIC2779 ignores very brief transients.

V

V

t

RST

See “Applications Information” for details.

June 2000 3 MIC2779

A

t

RST

MIC2779 Micrel

Functional Diagram

V

DD

V

BATT

Low-Voltage

Detect

V

LO

V

HI

LTH

HTH

* Pinout and polarity vary by device type.
See ordering information table.

High-Voltage

Detect

1.24V
Bandgap
Reference

GND

Delay

Line

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.

RSQ

One Shot

Q

MIC2779

/RST*

RST*

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

R1 1M R2 R3=−−Ω

Applications Information

Programming the Thresholds

The low-voltage threshold is calculated using:

R1 R2 R3

++

VV

=

BAT(lo) REF






R2 R3

+

The high-voltage threshold is calculated using:

R1 R2 R3

++

VV

=

BAT(hi) REF






R3

where, for both equations:

V 1.240V

=

REF

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 = R
A value such as 1MΩ for R
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
V

to ground is 3MΩ.

BAT

R1

R2

R3

V

BATT

604k
1%

56k
1%

340k
1%

Figure 1. Example Circuit

Once the desired trip points are determined, set the V
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:

TOTAL

MIC2779

VDD
LTH
HTH











TOTAL

is a reasonable value

/RST

RST

GND

BAT(hi)

Once R3 is determined, the equation for V

BAT(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 V

threshold allows calculation

BAT(lo)

of the two remaining resistor values.

1M

Ω

V 3.1V 1.24

BAT(lo)

==






R2 344k

+






R2 56k=Ω

R1 600k=Ω

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 negative-

.

going “glitches.” Very brief transients may exceed the V
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

140
120
100

80
60
40
20

0

MAX. TRANSIENT DURATION (µs)

1 10 100 1000

RESET COMP. OVERDRIVE, V

Response

REF–VLTH

(mV)

Figure 2. Input Transient Response

BAT(lo)

1M

Ω



V 1.24

BAT(hi)

=











R3

R3 344k=Ω

June 2000 5 MIC2779

MIC2779 Micrel

Package Information

1.90 (0.075) REF

0.95 (0.037) REF

3.02 (0.119)

2.80 (0.110)

0.50 (0.020)

0.35 (0.014)

1.75 (0.069)

1.50 (0.059)

1.30 (0.051)

0.90 (0.035)

0.15 (0.006)

0.00 (0.000)

SOT-23-5 (M5)

3.00 (0.118)

2.60 (0.102)

10°

0°

DIMENSIONS:

MM (INCH)

0.20 (0.008)

0.09 (0.004)

0.60 (0.024)

0.10 (0.004)

MIC2779 6 June 2000

MIC2779 Micrel

June 2000 7 MIC2779

MIC2779 Micrel

MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 [phone] FAX + 1 [phone] 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.

© 2000 Micrel Incorporated

MIC2779 8 June 2000