MAX687 Datasheet, PDF (1/12 Pages) Maxim Integrated Products – High-Accuracy, Low-Dropout Linear Regulators

19-0329; Rev 0; 12/94
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High-Accuracy, Low-Dropout
Linear Regulators
_______________General Description
The MAX687/MAX688/MAX689 low-dropout linear regula-
tors operate with an input-to-output voltage differential lim-
ited only by an external PNP transistor. Outputs are fixed
at 3.3V (MAX687/MAX688) or 3.0V (MAX689). The only
external components required are a PNP pass transistor
and output, compensation, and bypass capacitors. Base
drive to the external transistor is at least 10mA, permitting
output currents to exceed 1A when using high-gain tran-
sistors (β > 100). Output current limiting is implemented
by limiting the external transistor’s base current. Output
voltage monitoring and shutdown functions are included.
The 3.3V MAX687 automatically shuts down whenever
the output voltage drops below 2.96V. An internal
power-fail comparator also monitors the output and pro-
vides an early warning of low output voltage before the
device shuts down. When shut down, the output is
latched off until the ON input is pulsed. Turning off the
power supply in this way prevents battery damage due
to excessive discharge or cell-reversal. Typical applica-
tions include portable telephones and other battery-pow-
ered equipment where the power supply must be
disabled when the battery voltage is low.
The MAX688 and MAX689 do not have an automatic
shutdown function, and are identical except for their
output voltages. Each device has an active-low shut-
down-control input, used to turn its output on or off at
any time. As SHDN falls, the device enters a standby
mode before fully shutting down. When in standby, the
reference and comparators are fully operational, per-
mitting the transition from normal mode to standby
mode to occur at a precise voltage level on SHDN.
________________________Applications
High-Efficiency Linear Regulator
Battery-Powered Devices
Portable Instruments
Portable Telephones
Power Supply or Backup Supply for Memory
__________________Pin Configuration
____________________________Features
o Fixed Outputs:
3.3V (MAX687/MAX688)
3.0V (MAX689)
o Directly Drives External PNP Transistor
o 10mA Min Base-Current Drive for >1A Output
o Low Dropout Voltage:
100mV Dropout at 650mA Output (FZT749)
40mV Dropout at 200mA Output (FZT749)
0.8V Dropout at 4A Output
o Power-Fail Output Monitors the Output Voltage
o Automatic, Latched Shutdown when Output Falls Out
of Regulation (MAX687)
o Precision Threshold Shutdown Control
(MAX688/MAX689)
o Low Supply Current:
150µA Operating
<1µA Shutdown
o 2.7V to 11.0V Supply Range
o 8-Pin DIP/SO/µMAX Packages
o <2mV Line Transient with 3.4V to 3.6V Input
o Output Accuracy <±2%
______________Ordering Information
PART
TEMP. RANGE PIN-PACKAGE
MAX687CPA
0°C to +70°C
8 Plastic DIP
MAX687CSA
0°C to +70°C
8 SO
MAX687CUA
0°C to +70°C
8 µMAX
MAX687EPA
-40°C to +85°C
8 Plastic DIP
MAX687ESA
-40°C to +85°C
8 SO
Ordering Information continued at end of data sheet.
__________Typical Operating Circuit
+3.5V to +5V INPUT
Q1
FZT749
RB
12Ω
3.3V @ 500mA
TOP VIEW
IN ₁
(ON) SHDN 2
PFO 3
GND 4
MAX687
MAX688
MAX689
8 CC
7 BASE
6 BLIM
5 OUT
( ) ARE FOR MAX687
DIP/SO/µMAX
C1
2.2µF
ON
GND
BASE
IN
BLIM
OUT
MAX687 PFO
ON
CC
GND
C2
68µF
POWER-FAIL
OUTPUT
C3
10nF
________________________________________________________________ Maxim Integrated Products 1
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