MICREL MIC2778-2BM5, MIC2778-1BM5 Datasheet

MIC2778 Micrel

V

MIC2778

Voltage Monitor with Adjustable Hysteresis

Preliminary Information

General Description

The MIC2778 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) 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
not requiring built-in delay, see MIC833.

The IC’s power supply input is separate from the detector
inputs, allowing the MIC2778 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 MIC2778 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 not requiring built-in delay, see 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

Li-Ion

Cell

Ordering Information

Part Number Marking Accuracy Temperature Range Package

MIC2778-2BM5 UFB 2% –40°C to +85°C SOT-23-5
MIC2778-1BM5 UFA 1% –40°C to +85°C SOT-23-5

MIC5207-3.0BM5

IN

EN

604k
1%

56k
1%

340k
1%

MIC2778

LTH
HTH

V

BAT(hi)

V

BAT(lo)

RSTVDD

GND

= 3.6V
= 3.1V

100k

Cellular Telephone Battery Monitor

OUT

BYP

GND

470pF

OUT

3.0V

4.7µF

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

October 1999 1 MIC2778

MIC2778 Micrel

Pin Configuration

GND

2

HTH

13

VDDRST

LTH

45

SOT-23-5 (M5)

Pin Description

Pin Number Pin Name Pin Function

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

2 GND Ground
3 LTH Low-Voltage Threshold (Input): Analog input to a comparator. This is the

4 RST Reset (Output): Active-low, open-drain output. This output is asserted and

5 VDD Power Supply (Input): Independent supply input for internal circuitry.

level on this pin initially rises above V

, the delay generator cycles and the

REF

RST remains low for a minimum of 140ms.

voltage monitor input assigned to detect a low voltage condition. When the
level on this pin falls below V
latched until V

latched when V
remains latched until V

HTH

LTH

> V

<V

REF

REF

HTH

, RST is asserted and the condition is

REF

.

, indicating a low voltage condition. This state

> V

REF

.

MIC2778 2 October 1999

MIC2778 Micrel

V

HTH

V

BATT

V

LTH

0V

V

RSTH

V

RSTL

t

RST

t

RST

A

A

V

RST

Absolute Maximum Ratings (Note 1)

Supply Voltage (VDD) ..................................... –0.3V to +7V

Input Voltages (VHI, VLO) ............................... –0.3V to +7V

RST Output Current (I

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

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

RST

Operating Ratings (Note 2)

Supply Voltage (VDD) .................................. +1.5V to +5.5V

Input Voltages (V

Ambient Temperature Range (TA) ............. –40°C to +85°C

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

RST

, V

LTH

, V

) ............. –0.3V to +6.0V

HTH

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

RST

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 not asserted 1 2 µA
Input Leakage Current 5pA

10 nA

Reference Voltage 1.240 V

MIC2778-2 1.215 1.265 V
MIC2778-1 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
Voltage-Low Reset RST asserted, I

RST asserted, I

= 1.6mA, VDD ≥ 1.6V 0.3 V

SINK

= 100µA, VDD ≥ 1.2V, 0.4 V

SINK

Timing Diagram

Propagation delays not shown for clarity.
Note A. The MIC2778 ignores very brief transients.

October 1999 3 MIC2778

See “Applications Information” for details.