_______________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
____________________________Features
♦Fixed Outputs:
3.3V (MAX687/MAX688)
3.0V (MAX689)
♦Directly Drives External PNP Transistor
♦10mA Min Base-Current Drive for >1A Output
♦Low 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 Voltage
♦Automatic, Latched Shutdown when Output Falls Out
of Regulation (MAX687)
♦Precision Threshold Shutdown Control
(MAX688/MAX689)
♦Low Supply Current:
150µA Operating
<1µA Shutdown
♦2.7V to 11.0V Supply Range
♦8-Pin DIP/SO/µMAX Packages
♦<2mV Line Transient with 3.4V to 3.6V Input
♦Output Accuracy <±2%
______________Ordering Information
Ordering Information continued at end of data sheet.
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
________________________________________________________________
Maxim Integrated Products
1
MAX687
Q1
FZT749 RB
12Ω
BASE
GND
C1
2.2µF
IN BLIM
OUT
POWER-FAIL
OUTPUT
3.3V @ 500mA
PFO
CC
+3.5V to +5V INPUT
ON C3
10nF
ON
GND
C2
68µF
__________Typical Operating Circuit
1
2
3
4
8
7
6
5
CC
BASE
BLIM
OUT
GND
PFO
(ON) SHDN
IN
MAX687
MAX688
MAX689
DIP/SO/µMAX
TOP 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
MAX687CPA
MAX687CSA
MAX687CUA 0°C to +70°C
0°C to +70°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
8 Plastic DIP
8 SO
8 µMAX
EVALUATION KIT MANUAL
FOLLOWS DATA SHEET
MAX687EPA
MAX687ESA -40°C to +85°C
-40°C to +85°C 8 Plastic DIP
8 SO
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN = 3.8V, SHDN = VIN (MAX688/MAX689), RB= 0Ω, C1 = 2.2µF, C2 = 10µF, C3 = 10nF, TA= TMIN to 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
PFO Sink Current ...............................................................10mA
PFO Source 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 ≤10mA
RBis connected from BASE to BLIM (Ω),
RB= 0Ωto 100Ω
CONDITIONS
µF10C2Load Capacitance %2Start-Up Overshoot µs300Start-Up Time
mA
70 100 130
RB+ 5ΩRB+ 5ΩRB+ 5Ω
Base-Current Limit
V
3.2 3.3 3.4
VOUT
Output Voltage
V2.7 11.0VIN
Supply Voltage
mA10 20 40IBASE
BASE Sink Current < 0.02 1
11 25 µA
150 250
IGND
Supply Current
3.13 3.3 3.47
mV40VIN - V OUT
Dropout Voltage (Note 2)
mV/V
0.4 1.4
Line Regulation
mV45 60Load Regulation
UNITSMIN TYP MAXSYMBOLPARAMETER
VIN = 3.8V, IBASE = 1mA
3.8V ≤VIN ≤11.0V,
1µA ≤IBASE ≤10mA
PNP = FZT749, ILOAD = 200mA, C2 = 20µF
3.8V ≤VIN ≤11.0V,
IBASE = 1mA
MAX687/MAX688
MAX689 2.9 3.0 3.1
2.85 3.0 3.15
VIN = 3.5V, IBASE = 1mA
3.5V ≤VIN ≤11.0V,
1µA ≤IBASE ≤10mA
MAX689 3.5V ≤VIN ≤11.0V,
IBASE = 1mA 0.4 1.4
On
Standby,
MAX688/MAX689
Shutdown
LINEAR REGULATOR
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
_______________________________________________________________________________________ 3
Note 1: Minimum VIN for regulated VOUT depends 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 - VOUT when VOUT is 50mV below its value at VIN = VNOM + 1V.
Note 3: The start-up time specification is the time taken from ON or SHDN rising to BASE sinking current. VOUT rise 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, V NOM, is defined under the default conditions of testing: VIN = 3.8V, IBASE = 1mA, TA= TMIN to TMAX.
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 3.8V, SHDN = VIN (MAX688/MAX689), RB= 0Ω, C1 = 2.2µF, C2 = 10µF, C3 = 10nF, TA= TMIN to TMAX, unless otherwise
noted. Typical values are at TA= +25°C.)
Falling VOUT, comparators monitor VOUT
Glitch immunity
Rising SHDN, standby→on
Shutdown
Standby
Falling VOUT, comparators monitor VOUT
On, SHDN falling
Output turns on
CONDITIONS
µs100PFO, SHDN Transient Rejection
mV70SHDN Hysteresis 0.2VSSD
1.0 1.2VSSY V
1.25VSON
SHDN Threshold Voltages
mV110 170
VNOM -
VPFT
PFO Threshold Voltage Below
VNOM (Note 5)
mV7PFO Hysteresis
V2.96VSD
Shutdown Threshold Voltage
V
1.0VIH
ON Threshold Voltage
UNITSMIN TYP MAXSYMBOLPARAMETER
ISOURCE = 50µA, part on, VIN = 2.7V VVOUT - 0.3VOH
PFO Output Voltage High ISINK = 1.2mA, VIN = 2.7V V0.06 0.3VOL
PFO Output Voltage Low
Output remains off 0.2VIL nA0.2 100ON Input Leakage Current
Falling VOUT, com-
parators monitor VOUT V
3.07 3.13 3.19
VPFT
PFO Threshold Voltage MAX688
MAX689 2.77 2.85 2.89
V SHDN = 1.23V nA-25 25SHDN Input Current
10Hz ≤f ≤10kHz, ILOAD = 200mA
V PFO = 11V, V SHDN > 1.25V
ISINK = 1.2mA, VIN = 2.7V µA1
66
en
Output Noise Voltage
PFO Off Leakage Current V0.06 0.3VOL
PFO Output Voltage Low
10Hz ≤f ≤1MHz, ILOAD = 200mA µVRMS
105
Falling VOUT, comparators monitor VOUT mV20 70VPFT - VSD
Shutdown Threshold Voltage
Below VPFT
mV7PFO Hysteresis
MAX688/MAX689: SHDN, PFO
MAX687: ON, PFO, SHDN
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
4 _______________________________________________________________________________________
__________________________________________Typical Operating Characteristics
(Circuits of Figures 1 and 2, VIN = 5V, Q1 = FZT749, TA = +25°C, unless otherwise noted.)
3.29679
3.29904
3.29455
3.29231
3.29007
3.28783
3.30128
3.30352
3.30576
3.30800
3.31024
3.31248
3.31472
3.31696
3.31920
3.32145
0 50 100
NUMBER OF UNITS 250200150
MAX688
OUTPUT VOLTAGE DISTRIBUTION
MAX687/9-01
OUTPUT VOLTAGE (V)
3.28365
3.28722
3.29078
3.29435
3.29792
3.30149
3.30505
3.30862
3.31219
3.31576
3.31932
3.32289
0 50 100 250200150
MAX687
OUTPUT VOLTAGE DISTRIBUTION
MAX687/9-02
OUTPUT VOLTAGE (V)
NUMBER OF UNITS
2.98975
2.99150
2.99324
2.99499
2.99674
2.99848
3.00023
3.00198
3.00372
3.00547
3.00721
3.00896
3.01071
3.01245
3.01420
3.01595
050 100 250200150
MAX689
OUTPUT VOLTAGE DISTRIBUTION
MAX687/9-03
OUTPUT VOLTAGE (V)
NUMBER OF UNITS
7
6
5
4
3
2
1
00 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
GND CURRENT vs. DROPOUT VOLTAGE
MAX687/9-7
VIN - VOUT (V)
GND CURRENT (mA)
300mA LOAD
100mA LOAD
10mA LOAD
0
0.05
0.10
0.15
0.20
0.25
0.30
0 200 600 1000 1400 1800
DROPOUT VOLTAGE
vs. LOAD CURRENT
MAX687/9-05
LOAD CURRENT (mA)
VIN - VOUT (V)
Q1 = FZT749
RB = 0Ω
OBSERVE MAXIMUM POWER
DISSIPATION LIMIT OF
EXTERNAL PASS TRANSISTOR. 0
1
2
3
4
5
6
0 200 400 600 800 1000 1200
GND CURRENT
vs. LOAD CURRENT
MAX687/9-06
LOAD CURRENT (mA)
GND CURRENT (mA)
7
6
5
4
3
2
1
00812345 76
GND CURRENT vs. DROPOUT VOLTAGE
MAX687/9-8
VIN - VOUT (V)
GND CURRENT (mA)
300mA LOAD
100mA LOAD 10mA LOAD
146
126
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
130
128
134
132
138
136
142
144
140
MAX687/9-9
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
-55 -25 0 25 50 75 100 125
1.0
00 200 600 1000
DROPOUT VOLTAGE
vs. LOAD CURRENT
0.2
0.1
0.4
0.3
0.6
0.5
0.8
0.9
0.7
MAX687/9-5
LOAD CURRENT (mA)
VIN - VOUT (V)
400 800
Q1 = 2N2907
RB = 0Ω
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
_______________________________________________________________________________________
5
0
0.0500
0.1000
0.1500
0.2000
0.2500
0.3000
-55 -25 0 25 50 75 100 125
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
MAX687/9-10
TEMPERATURE (°C)
SHUTDOWN SUPPLY CURRENT (µA)
3.280
3.285
3.290
3.295
3.300
3.305
3.310
3.315
OUTPUT VOLTAGE
vs. TEMPERATURE
MAX687/9-11
TEMPERATURE (°C)
OUTPUT VOLTAGE (V)
-55 -25 0 25 50 75 100 125
ILOAD = 70mA
C1 = 2.2µF
C2 = 20µF
C3 = 10nF
LINE-TRANSIENT RESPONSE
VOUT
3.3V
1mV/div
VIN
3.6V
VIN
3.4V
2ms/div ILOAD = 200mA
C1 = 2.2µF
C2 = 20µF
C3 = 10nF
LINE-TRANSIENT RESPONSE
VOUT
3.3V
1mV/div
VIN
3.6V
VIN
3.4V
2ms/div
VIN = 3.4V
LOAD-TRANSIENT RESPONSE
VOUT
3.3V
10mV/div
500mA
0mA
100µs/div
ILOAD
200mA/div
VIN = 3.5V
LOAD-TRANSIENT RESPONSE
VOUT
3.3V
10mV/div
500mA
0mA
100µs/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 = 2.2µF
C2 = 68µF
C3 = 10nF
MAX687/MAX688
POWER-UP AND EXIT FROM SHUTDOWN
VIN
5V/div
VOUT
1V/div
SHDN
5V/div
1ms/div
80
010 100 1k 10k 100k
MAX687/MAX688
RIPPLE REJECTION vs. FREQUENCY
10
20
MAX687/9-16
FREQUENCY (Hz)
RIPPLE REJECTION (dB)
30
40
50
60
70
C2 = 20µF
VIN = 4.3V Min
ILOAD = 20mA
VIN = 3.6V Min
ILOAD = 200mA
2
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
6 _______________________________________________________________________________________
______________________________________________________________Pin Description
NAME FUNCTION
1IN Positive input voltage, 2.7V to 11.0V
2
ON
(MAX687)
ON activates the regulator when pulsed high. In order for the regulator to remain on, ON must remain high
until VOUT exceeds 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 VIN if not used.
PIN
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).
3 PFO Power-Fail Output. PFO trips when VOUT is 170mV below nominal VOUT at IBASE = 1mA. PFO sources and
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.
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.
6 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.
5 OUT Regulator Output. MAX687/MAX688, 3.3V; MAX689, 3.0V.
4 GND Ground
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).
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
Table 1. Device Functions
FUNCTION MAX687 MAX688 MAX689
VOUT 3.3V 3.3V 3.0V
Shutdown
Control
Automatic at low
VOUT. Latched.
Use ON to start.
External
SHDN External
SHDN
PFO Sources & Sinks Open Drain Open Drain
shuts down. Once the MAX687 is shut down, it can
only be turned on again when (a) the ON pin is pulsed
high, and (b) the conditions that triggered shutdown
have changed (e.g., the load has been reduced or the
input voltage has increased). In order for the MAX687
to latch into its on state, the ON pulse must remain high
until the output voltage has risen above the shutdown
threshold. The internal shutdown can be used to pre-
vent deep discharge of a battery, for example, to pro-
vide “self backup” of CMOS RAM or to protect the
battery itself.
The RC circuit attached to the ON input in Figure 1
achieves automatic start-up at power-on by delivering a
brief pulse whenever the input voltage is suddenly
applied. This circuit is not suitable for applications
where the input voltage rises slowly. The RC values
should be chosen to keep ON high until the output rises
above about 3.13V. The values shown in Figure 1 for
C4 and R1 (0.1µF and 10kΩ) are suitable for most
applications. To ensure start-up when the input voltage
is very close to the circuit’s dropout voltage, when the
circuit is used to drive a very large capacitive load, or
for high-power circuits (ILOAD > 3A), increase the value
of R1 to increase the ON pulse width.
The 3.3V MAX688 and the 3.0V MAX689 incorporate
the same PFO warning whenever VOUT droops.
However, the MAX688/MAX689 do not automatically
shut down when the output voltage drops even further.
Instead, the SHDN input controls external shutdown.
As SHDN is pulled low, the chip first enters a low-cur-
rent standby state (<25µA). The threshold at which
standby mode is entered is precisely controlled (±2%)
so the output can be turned off at a well-defined point.
70mV of hysteresis between the standby and on states
prevents chatter between the two modes. The voltage
applied to the SHDN pin can be derived from a resis-
tive divider from VIN. When VSHDN is less than 1.2V,
the output is off. The device is fully shut down (<1µA)
when SHDN is pulled below 200mV. SHDN is not
latched, and as SHDN is raised, the MAX688/MAX689
exit shutdown and enter the standby mode. At the
higher SHDN threshold, the output is turned on.
Figure 1 shows a typical circuit for the MAX687, and
Figure 2 shows the same circuit configured for the
MAX688/MAX689.
The accuracy of the output current limit depends on
accurate knowledge of the PNP pass transistor’s cur-
rent gain (hFE). With RB= 12Ω, BLIM limits base cur-
rent to 6mA (IBASE = 0.1V / (RB+ 5Ω)). See
Base-
Current Limiting
section.
The PFO comparators on all three devices, and the internal
shutdown comparator on the MAX687, reject high-speed
spikes (<100µs). This reduces the PFOoutput’s noise sen-
sitivity, and stops the MAX687 from being shut down inad-
vertently when there is noise on the input supply.
_______________Transistor Selection
Specifications
The PNP pass transistor must meet specifications for
•current gain,
•power dissipation, and
•collector current.
The hFE influences the maximum output current the cir-
cuit can deliver. The largest guaranteed output current
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
_______________________________________________________________________________________ 7
MAX687
OUT
3.3V @ 500mA
POWER FAIL
PFO
CC
C1
2.2µF
C4
0.1µFBLIM
GND
BASE
Q1 FZT749
RB 12Ω
C3
10nF
IN
ON
+5V INPUT
GND
R1
10kΩ
ON CAN BE DRIVEN DIRECTLY FROM LOGIC WHEN R1 AND C4 ARE NOT USED.
C2
68µF
Figure 1. MAX687 Operating Circuit
MAX688
MAX689
OUT
3.3V/ 3.0V @ 500mA
POWER FAIL
PFO
CC
C1
2.2µF
BLIM
GND
BASE
Q1 FZT749
RB 12Ω
C3
10nF
IN
SHDN
+5V INPUT
GND
R2
100k
C2
68µF
ON / OFF
Figure 2. MAX688/MAX689 Operating Circuit
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
8 _______________________________________________________________________________________
is given by ILOAD(MAX) = 10mA x hFE(MIN). The tran-
sistor’s rated power dissipation must exceed the actual
power dissipated in the transistor. The power dissipat-
ed (PD) equals the maximum load current (ILOAD(MAX))
times the maximum input to output voltage differential:
PD = ILOAD(MAX) x (VIN(MAX) - VOUT). The rated tran-
sistor collector current must exceed the maximum load
current. Suitable transistors include the Zetex FZT749,
and the 2N2907A (see Table 2).
Base-Current Limiting
A comparator monitors the voltage across the external
base-current-limiting resistor (between BASE and
BLIM). This sets the maximum base current. If BASE
and BLIM are shorted, base current is limited nominally
to 20mA due to an internal 5Ωresistor in series with the
external resistance. Choose the base-current-limiting
resistor, RB, so the drop across it at rated load is
approximately 50mV.
The base drive is controlled so the voltage on BLIM is
limited to 100mV below the voltage on BASE; with a
50mV nominal drop across RB+ 5Ω, base-current drive
is limited to twice the nominal. This limits base current
when the external PNP is heavily saturated, such as
when the regulator is in dropout due to low input volt-
age. In addition, if the external PNP’s hFE is defined
within reasonable limits, base-current control effectively
limits output current without a dropout voltage penalty.
________________Capacitor Selection
Bypass Capacitor (C1)
Connect a bypass capacitor from IN to GND. 4.7µF
makes the circuit insensitive to layout, and is sufficient
for any load. Smaller values may be used—down to
0.33µF—with low-ESR capacitors, good board layout,
and a low-impedance incoming supply.
Connect the bypass capacitor directly between pins 1
and 4 of the IC, using short leads. Connect the emitter
of the PNP transistor directly to the bypass capacitor
using a very short trace.
Output Capacitor (C2)
The output filter capacitor must be at least 10µF. For
currents above 100mA, use 1µF of capacitance for
every 10mA of load current (e.g., 20µF for 200mA load,
50µF for 500mA). Low-ESR capacitors give best stabili-
ty and transient response. Ensure that the capacitor’s
ESR is less than 1% of the load resistance. See Table 2
for a list of manufacturers. Sanyo OS-CON capacitors
are recommended for applications operating at temper-
atures below 0°C.
Compensation Capacitor (C3)
Connect a compensation capacitor from CC to GND.
10nF is recommended, although higher values (up to
100nF) may also be used. Higher C3 values eliminate
power-on overshoot, but extend power-up times.
Current flowing into or out of CC causes the regulator’s
reference voltage to change, resulting in shifted output
voltage and trip thresholds. Use non-polarized capaci-
tors (e.g., ceramic, polyester, etc.) to keep leakage cur-
rents below 25nA. Aluminum and tantalum electrolytic
capacitors are unsuitable because of their high leakage
currents.
__________________Power-Fail Output
The PFO output trips when VOUT is 170mV below nomi-
nal VOUT at IBASE = 1mA. PFO sources and sinks cur-
rent in the MAX687, but is an open drain in the
MAX688/MAX689 and only sinks current. When shut
down, PFO is always low regardless of the voltage at
OUT. Leave PFO open if it is not used.
R mV x h
I
BFE(MIN)
LOAD(MAX)
=
()
−Ω
50 5
__________Applications Information
High-Power Output Circuit
Figure 3 shows a pseudo-Darlington transistor configu-
ration to increase load-current capability and maintain
a low dropout voltage with a 4A load. A heatsink must
be added when high power is dissipated in the pass
transistor.
Figure 4 shows the (VIN - VOUT) voltage required to
maintain regulation for different load currents. Figure 5
shows an oscilloscope plot of the transient response of
a 200mA to 4A load step.
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
_______________________________________________________________________________________ 9
MAX688
MAX689
OUT
3.3V/ 3.0V @ 4A
PFO
CC
C1
220µF
+5V INPUT
BLIM
GND
BASE
Q2
2N4403
C3
10nF
IN
SHDN
R2
100kΩ
C2
470µF
x3
Q1
T1P42
10Ω1kΩ
ON / OFF POWER FAIL
Figure 3. 4A Low-Dropout Circuit
1.0
00 40001000 2000 3000
DROPOUT VOLTAGE vs. LOAD CURRENT
0.2
0.1
0.4
0.3
0.6
0.5
0.8
0.9
0.7
MAX687/9-04
LOAD CURRENT (mA)
VIN - VOUT (V)
Q1 = TIP42
Q2 = 2N4403
BASE = BLIM
Figure 4. Dropout Voltage vs. Load Current of Figure 3
VOUT
+3.3V, 20mV/div
IOUT
1A/div
50µs/div
LOAD-TRANSIENT RESPONSE
Figure 5. Transient Response for a 200mA to 4A Load Step
Using Circuit of Figure 3
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
10 ______________________________________________________________________________________
Table 2a. Component Suppliers
DEVICE MANUFACTURER PRODUCTION
METHOD
267 series Matsuo
Surface MountF95 Tantalum series Nichicon
595 Tantalum series Sprague
OS-CON series
low-ESR organic
semiconductor Sanyo Through-Hole
LXF series United Chemi-Con
ZTX749 Zetex
Through-Hole
T1P42 Motorola
2N4403 Motorola
2N2907A Motorola
CMPT2907A Central Semiconductor
Surface Mount
PZT2907AT1 Motorola
FZT749 Zetex
CAPACITORS
BIPOLAR TRANSISTORS
Table 2b. Manufacturers’ Phone
and Fax Numbers
MANU-
FACTURER COUNTRY TELEPHONE FAX
Central
Semiconductor USA (516) 435-1110 (516) 435-1824
Matsuo USA (714) 969-2491 (714) 960-6492
Motorola USA (602) 244-3370 (602) 244-4015
Nichicon USA (708) 843-7500 (708) 843-2798
Japan +81-7-5231-
8461 +81-7-5256-
4158
Sanyo USA (619) 661-6835 (619) 661-1055
Japan +81-7-2070-
6306 +81-7-2070-
1174
Sprague USA (603) 224-1961 (603) 224-1430
United
Chemi-Con USA (714) 255-9500 (714) 255-9400
USA (516) 543-7100 (516) 864-7630
Zetex UK +44-61-627-
5105 +44-61-627-
5467
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
______________________________________________________________________________________ 11
_Ordering Information (continued)
PART
MAX688CPA
MAX688CSA
MAX688CUA 0°C to +70°C
0°C to +70°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
8 Plastic DIP
8 SO
8 µMAX
MAX688EPA
MAX688ESA -40°C to +85°C
-40°C to +85°C 8 Plastic DIP
8 SO
MAX689CPA
MAX689CSA
MAX689CUA 0°C to +70°C
0°C to +70°C
0°C to +70°C 8 Plastic DIP
8 SO
8 µMAX
MAX689EPA
MAX689ESA -40°C to +85°C
-40°C to +85°C 8 Plastic DIP
8 SO
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.
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
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.
________________________________________________________Package Information
L
α
C
A1B
DIM
A
A1
B
C
D
E
e
H
L
α
MIN
0.036
0.004
0.010
0.005
0.116
0.116
0.188
0.016
0°
MAX
0.044
0.008
0.014
0.007
0.120
0.120
0.198
0.026
6°
MIN
0.91
0.10
0.25
0.13
2.95
2.95
4.78
0.41
0°
MAX
1.11
0.20
0.36
0.18
3.05
3.05
5.03
0.66
6°
INCHES MILLIMETERS
8-PIN µMAX
MICROMAX SMALL OUTLINE
PACKAGE
0.650.0256
A
e
E H
D
0.101mm
0.004 in
