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MAX688CUA+-MAX688CUA-T
High-Accuracy, Low-Dropout Linear Regulators
_______________General DescriptionThe 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 (b > 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 SHDNfalls, 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.
________________________ApplicationsHigh-Efficiency Linear Regulator
Battery-Powered Devices
Portable Instruments
Portable Telephones
Power Supply or Backup Supply for Memory
____________________________FeaturesFixed Outputs:
3.3V (MAX687/MAX688)
3.0V (MAX689) Directly Drives External PNP Transistor10mA Min Base-Current Drive for >1A OutputLow Dropout Voltage:
100mV Dropout at 650mA Output (FZT749)
40mV Dropout at 200mA Output (FZT749)
0.8V Dropout at 4A Output Power-Fail Output Monitors the Output VoltageAutomatic, Latched Shutdown when Output Falls Out
of Regulation (MAX687)Precision Threshold Shutdown Control
(MAX688/MAX689)Low Supply Current:
150μA Operating
<1μA Shutdown2.7V to 11.0V Supply Range8-Pin DIP/SO/μMAX Packages<2mV Line Transient with 3.4V to 3.6V InputOutput Accuracy <±2%
______________Ordering Information
Ordering Information continued at end of data sheet.igh-Accuracy, Low-Dropout
Linear Regulators
________________________________________________________________Maxim Integrated Products1MAX687
Q1
FZT749
RB
12W
BASE
GND
C1
2.2mF
BLIM
OUT
POWER-FAIL
OUTPUT
3.3V @ 500mA
PFO
+3.5V to +5V INPUT
C3
10nF
GND
C2
68mF
__________Typical Operating CircuitBASE
BLIM
OUTGND
PFO
(ON) SHDN
MAX687
MAX688
MAX689
DIP/SO/mMAXTOP VIEW
( ) ARE FOR MAX687
__________________Pin Configuration
Call toll free 1-800-998-8800 for free samples or literature.19-0329; Rev 0; 12/94
PART
MAX687CPAMAX687CSA
MAX687CUA0°C to +70°C
0°C to +70°C
0°C to +70°C
TEMP. RANGEPIN-PACKAGE8 Plastic DIP
8 SO
8 μMAX
EVALUATION KIT MANUAL
FOLLOWS DATA SHEETMAX687EPA
MAX687ESA-40°C to +85°C
-40°C to +85°C8 Plastic DIP
8 SO
igh-Accuracy, Low-DropoutLinear Regulators_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VIN= 3.8V, SHDN= VIN(MAX688/MAX689), RB= 0Ω, C1 = 2.2μF, C2 = 10μF, C3 = 10nF, TA= TMINto TMAX, unless otherwise
noted. Typical values are at TA= +25°C.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Input Supply Voltage IN to GND............................................12V
Terminal Voltages to GND
PFO(MAX687)........................................-0.3V to VOUT+ 0.3V
PFO(MAX688/MAX689) ......................................-0.3V to 12V
All Remaining Pins.....................................-0.3V to VIN+ 0.3V
PFOSink Current ...............................................................10mA
PFOSource Current (MAX687)...........................................10mA
Continuous Power Dissipation (TA= +70°C)
Plastic DIP (derate 9.09mW/°C above +70°C)............727mW
SO (derate 5.88mW/°C above +70°C).........................471mW
μMAX (derate 4.1mW/°C above +70°C)......................330mW
Operating Temperature Ranges
MAX68_C_A .......................................................0°C to +70°C
MAX68_E_A ....................................................-40°C to +85°C
Storage Temperature Range.............................-65°C to +165°C
Lead Temperature (soldering, 10sec).............................+300°C
MAX687/MAX688
(Note 1)
VBASE= VIN- 1V
PNP = FZT749, ILOAD= 100mA (Note 4)
VIN= 3.8V,
PNP = FZT749,
no load
(Note 3)
1μA ≤IBASE≤10mAis connected from BASE to BLIM (Ω), = 0Ωto 100Ω
CONDITIONS10C2Load Capacitance2Start-Up Overshoot300Start-Up Time70100130+ 5ΩRB+ 5ΩRB+ 5ΩBase-Current Limit
VOUTOutput Voltage2.711.0VINSupply Voltage102040IBASEBASE Sink Current
< 0.02125μA
IGNDSupply Current
3.133.33.4740VIN- VOUTDropout Voltage (Note 2)
mV/V
Line Regulation4560Load Regulation
UNITSMINTYPMAXSYMBOLPARAMETERVIN= 3.8V, IBASE= 1mA
3.8V ≤VIN≤11.0V,
1μA ≤IBASE≤10mA
PNP = FZT749, ILOAD= 200mA, C2 = 20μF
3.8V ≤VIN≤11.0V,
IBASE= 1mAMAX687/MAX688
MAX689
VIN= 3.5V, IBASE= 1mA
3.5V ≤VIN≤11.0V,
1μA ≤IBASE≤10mA
MAX6893.5V ≤VIN≤11.0V,
IBASE= 1mA0.41.4
Standby,
MAX688/MAX689
Shutdown
LINEAR REGULATOR
igh-Accuracy, Low-DropoutLinear Regulators
_______________________________________________________________________________________3
Note 1:Minimum VINfor regulated VOUTdepends on the characteristics of the external PNP transistor, and on the load. The refer-
ence and comparators are functional down to the minimum voltage specified, but the output may not be in regulation.
Note 2: Dropout voltage is defined as VIN- VOUTwhen VOUTis 50mV below its value at VIN= VNOM+ 1V.
Note 3:The start-up time specification is the time taken from ON or SHDNrising to BASE sinking current. VOUTrise time is longer
and is a function of load capacitance, C2, and load resistance, RL.
Note 4:Minimum load capacitance is a function of RL. Minimum C2 = 10μF for loads up to 100mA and 1μF/10mA for higher loads.
ESR of C2 should be no larger than 1/100 of RL. Guaranteed by design.
Note 5:The nominal output voltage, VNOM, is defined under the default conditions of testing: VIN= 3.8V, IBASE= 1mA, TA= TMINto TMAX.
ELECTRICAL CHARACTERISTICS (continued)(VIN= 3.8V, SHDN= VIN(MAX688/MAX689), RB= 0Ω, C1 = 2.2μF, C2 = 10μF, C3 = 10nF, TA= TMINto TMAX, unless otherwise
noted. Typical values are at TA= +25°C.)
Falling VOUT, comparators monitor VOUT
Glitch immunity
Rising SHDN, standbyfion
Shutdown
Standby
Falling VOUT, comparators monitor VOUT
On, SHDNfalling
Output turns on
CONDITIONS100PFO, SHDNTransient Rejection70SHDNHysteresis
0.2VSSD
1.01.2VSSYV
1.25VSON
SHDNThreshold Voltages110170VNOM-
VPFT
PFOThreshold Voltage Below
VNOM(Note 5)7PFOHysteresis2.96VSDShutdown Threshold Voltage1.0VIHON Threshold Voltage
UNITSMINTYPMAXSYMBOLPARAMETERISOURCE= 50μA, part on, VIN= 2.7VVVOUT - 0.3VOHPFOOutput Voltage High
ISINK= 1.2mA, VIN= 2.7VV0.060.3VOLPFOOutput Voltage Low
Output remains off0.2VIL0.2100ON Input Leakage Current
Falling VOUT, com-
parators monitor VOUTV3.073.133.19VPFTPFOThreshold VoltageMAX688
MAX6892.772.852.89
V SHDN= 1.23VnA-2525SHDNInput Current
10Hz ≤f ≤10kHz, ILOAD= 200mA
V PFO= 11V, V SHDN> 1.25V
ISINK= 1.2mA, VIN= 2.7V1enOutput Noise Voltage
PFOOff Leakage Current0.060.3VOLPFOOutput Voltage Low
10Hz ≤f ≤1MHz, ILOAD= 200mAμVRMS105
Falling VOUT, comparators monitor VOUTmV2070VPFT - VSDShutdown Threshold Voltage
Below VPFT7PFOHysteresis
MAX688/MAX689: SHDN, PFO
MAX687: ON, PFO, SHDN
igh-Accuracy, Low-DropoutLinear Regulators_______________________________________________________________________________________
__________________________________________Typical Operating Characteristics(Circuits of Figures 1 and 2, VIN= 5V, Q1 = FZT749, TA = +25°C, unless otherwise noted.)
NUMBER OF UNITS
MAX688
OUTPUT VOLTAGE DISTRIBUTION
MAX687/9-01
(V)
MAX687
OUTPUT VOLTAGE DISTRIBUTION
MAX687/9-02
T V
E (V
NUMBER OF UNITS
MAX689
OUTPUT VOLTAGE DISTRIBUTION
MAX687/9-03
(V)
NUMBER OF UNITS0.10.20.30.40.50.60.70.80.91.0
GND CURRENT vs. DROPOUT VOLTAGEMAX687/9-7
VIN - VOUT (V)
(m
300mA LOAD
100mA LOAD
10mA LOAD
DROPOUT VOLTAGE
vs. LOAD CURRENT
AX687/9-05
LOAD CURRENT (mA)
- V
(V
Q1 = FZT749
RB = 0W
OBSERVE MAXIMUM POWERDISSIPATION LIMIT OF
EXTERNAL PASS TRANSISTOR.20040060080010001200
GND CURRENT
vs. LOAD CURRENTAX687/9-06
LOAD CURRENT (mA)
(m81234576
GND CURRENT vs. DROPOUT VOLTAGEMAX687/9-8
VIN - VOUT (V)
T (m
300mA LOAD
100mA LOAD
10mA LOAD
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
AX687/9-9
TEMPERATURE (°C)
T (m
DROPOUT VOLTAGE
vs. LOAD CURRENT
MAX687/9-5
LOAD CURRENT (mA)
VIN - VO
T (V
Q1 = 2N2907RB = 0W
igh-Accuracy, Low-DropoutLinear Regulators
_______________________________________________________________________________________5SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
MAX687/9-10
TEMPERATURE (°C)
T (m
OUTPUT VOLTAGE
vs. TEMPERATURE
MAX687/9-11
TEMPERATURE (°C)
E (V
ILOAD = 70mA
C1 = 2.2mF
C2 = 20mF
C3 = 10nF
LINE-TRANSIENT RESPONSEVOUT
3.3V
1mV/div
VIN
3.6V
VIN
3.4V
2ms/divILOAD = 200mA
C1 = 2.2mF
C2 = 20mF
C3 = 10nF
LINE-TRANSIENT RESPONSEVOUT
3.3V
1mV/div
VIN
3.6V
VIN
3.4V
2ms/div
VIN = 3.4V
LOAD-TRANSIENT RESPONSEVOUT
3.3V
10mV/div
500mA
0mA
100ms/div
ILOAD
200mA/div
VIN = 3.5V
LOAD-TRANSIENT RESPONSEVOUT
3.3V
10mV/div
500mA
0mA
100ms/div
ILOAD
200mA/div
____________________________Typical Operating Characteristics (continued)(Circuits of Figures 1 and 2, VIN= 5V, Q1 = FZT749, TA = +25°C, unless otherwise noted.)
ILOAD = 500mA
C1 = 2.2mF
C2 = 68mF
C3 = 10nF
MAX687/MAX688
POWER-UP AND EXIT FROM SHUTDOWNVIN
5V/div
VOUT
1V/div
SHDN
5V/div
1ms/div1001k10k100k
MAX687/MAX688
RIPPLE REJECTION vs. FREQUENCYMAX687/9-16
FREQUENCY (Hz)
TIO
(d
C2 = 20mF
VIN = 4.3V Min
ILOAD = 20mA
VIN = 3.6V Min
ILOAD = 200mA
igh-Accuracy, Low-DropoutLinear Regulators_______________________________________________________________________________________
______________________________________________________________Pin Description
NAMEFUNCTIONINPositive input voltage, 2.7V to 11.0V
(MAX687)
ON activates the regulator when pulsed high. In order for the regulator to remain on, ON must remain high
until VOUTexceeds the internal shutdown threshold voltage. The MAX687 is shut down when VOUT< 2.96V,
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 VINif not used.
PINSHDN
(MAX688/
MAX689)
SHDNis 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 SHDNto IN if the shutdown func-
tion is not used. PFOis low when SHDNis low (below 0.2V).PFO
Power-Fail Output. PFOtrips when VOUTis 170mV below nominal VOUTat IBASE= 1mA. PFOsources and
sinks current in the MAX687, but is an open drain in the MAX688/MAX689. When shut down, PFOis always
low and sinks current. Leave PFOopen if not used.BASEBase 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.BLIM
Base current limit. A resistor (RB) connected between BASE and BLIM sets the maximum base drive to the
PNP transistor: IBASE≤0.1V / (RB + 5Ω). This limits quiescent current rise during dropout and also pro-
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.OUTRegulator Output. MAX687/MAX688, 3.3V; MAX689, 3.0V.GNDGroundCCCompensation Capacitor. Connect a non-polarized capacitor (10nF to 100nF) from CC to GND.
_______________Detailed DescriptionThe 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).
The MAX687’s output voltage is internally monitored; a
falling VOUTis signaled by PFOgoing 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. PFOtrips at a minimum of
110mV below the nominal VOUT, and shutdown occurs
by 2.96V. PFOis guaranteed to trip before the device
Table 1. Device Functions
FUNCTIONMAX687MAX688MAX689VOUT3.3V3.3V3.0V
Shutdown
Control
Automatic at low
VOUT. Latched.
Use ON to start.
External
SHDN
External
SHDN
PFOSources & SinksOpen DrainOpen Drain
