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MAX687 Schematic ( PDF Datasheet ) - Maxim Integrated

Teilenummer MAX687
Beschreibung High-Accuracy / Low-Dropout Linear Regulators
Hersteller Maxim Integrated
Logo Maxim Integrated Logo 




Gesamt 12 Seiten
MAX687 Datasheet, Funktion
19-0329; Rev 0; 12/94
EVFAOLLULAOTWIOSNDKAITTAMSAHNEUEATL
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
12
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
Call toll free 1-800-998-8800 for free samples or literature.






MAX687 Datasheet, Funktion
High-Accuracy, Low-Dropout
Linear Regulators
______________________________________________________________Pin Description
PIN NAME
FUNCTION
1 IN Positive input voltage, 2.7V to 11.0V
ON activates the regulator when pulsed high. In order for the regulator to remain on, ON must remain high
ON until VOUT exceeds the internal shutdown threshold voltage. The MAX687 is shut down when VOUT < 2.96V,
(MAX687) and remains latched off until ON is pulsed high. When powered up, the MAX687 does not start up until ON
is pulsed high. Connect to VIN if not used.
2
2
SHDN
(MAX688/
MAX689)
SHDN is a three-level input that controls the mode of operation. The device is on when V SHDN > 1.25V.
The output is disabled and the supply current is reduced (IIN < 25µA, standby mode) when V SHDN < 1.2V,
and is fully off (IIN < 1µA, shutdown mode) when V SHDN < 0.2V. Connect SHDN to IN if the shutdown func-
tion is not used. PFO is low when SHDN is low (below 0.2V).
Power-Fail Output. PFO trips when VOUT is 170mV below nominal VOUT at IBASE = 1mA. PFO sources and
3
PFO
sinks current in the MAX687, but is an open drain in the MAX688/MAX689. When shut down, PFO is always
low and sinks current. Leave PFO open if not used.
4 GND Ground
5 OUT Regulator Output. MAX687/MAX688, 3.3V; MAX689, 3.0V.
Base current limit. A resistor (RB) connected between BASE and BLIM sets the maximum base drive to the
PNP transistor: IBASE 0.1V / (RB + 5). This limits quiescent current rise during dropout and also pro-
6 BLIM vides current limiting without using a current-sense resistor in the collector of the external PNP, thus not
impacting dropout. Output current limiting accuracy depends on how well the external PNP beta (hFE) is
controlled. Connect to BASE if not used.
7
BASE
Base drive for the external PNP transistor. Current limiting is controlled using a resistor (RB) connected
between BASE and BLIM. For maximum output current, connect BASE to BLIM.
8 CC Compensation Capacitor. Connect a non-polarized capacitor (10nF to 100nF) from CC to GND.
_______________Detailed Description
The MAX687/MAX688/MAX689 are precision low-
dropout linear regulators employing external PNP tran-
sistors to achieve a wide range of output currents at
voltages of 3.0V or 3.3V. The maximum base current
for the PNP can be limited using a resistor. Limiting the
base drive keeps high currents from being wasted
when the device is in dropout (e.g., at low input volt-
ages), and limits the regulator’s output current. The
dropout voltage is limited only by the PNP transistor’s
VCE(SAT). The Power-Fail Output (PFO) goes low when
the output voltage drops 170mV below the nominal
level.
The three devices differ in their output voltages, in their
shutdown-control functions, and in PFO’s output drive
(see Table 1).
Table 1. Device Functions
FUNCTION
VOUT
Shutdown
Control
PFO
MAX687
3.3V
Automatic at low
VOUT. Latched.
Use ON to start.
Sources & Sinks
MAX688
3.3V
External
SHDN
Open Drain
MAX689
3.0V
External
SHDN
Open Drain
The MAX687’s output voltage is internally monitored; a
falling VOUT is signaled by PFO going low. As the out-
put falls further, the MAX687 automatically enters a low-
power shutdown mode, where the base drive to the
external PNP is cut off. PFO trips at a minimum of
110mV below the nominal VOUT, and shutdown occurs
by 2.96V. PFO is guaranteed to trip before the device
6 _______________________________________________________________________________________

6 Page









MAX687 pdf, datenblatt
High-Accuracy, Low-Dropout
Linear Regulators
________________________________________________________Package Information
C
A
0.101mm
e 0.004 in
B A1
INCHES
DIM
MIN MAX
MILLIMETERS
MIN MAX
A 0.036 0.044 0.91 1.11
α A1 0.004 0.008 0.10 0.20
B 0.010 0.014 0.25 0.36
C 0.005 0.007 0.13 0.18
D 0.116 0.120 2.95 3.05
E 0.116 0.120 2.95 3.05
L
e 0.0256
0.65
H 0.188 0.198 4.78 5.03
L 0.016 0.026 0.41 0.66
α 0° 6° 0° 6°
EH
8-PIN µMAX
MICROMAX SMALL OUTLINE
PACKAGE
D
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1994 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.

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