MAXIM MAX689ESA

19-0329; Rev 0; 12/94
NUAL
KIT MA
ATION
U
EET
L
H
A
S
V
A
E
T
WS DA
FOLLO
High-Accuracy, Low-Dropout
Linear Regulators
____________________________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%
________________________Applications
High-Efficiency Linear Regulator
Battery-Powered Devices
Portable Instruments
Portable Telephones
Power Supply or Backup Supply for Memory
______________Ordering Information
PART
TEMP. RANGE
0°C to +70°C
8 Plastic DIP
MAX687CSA
MAX687CUA
MAX687EPA
MAX687ESA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
8 SO
8 µMAX
8 Plastic DIP
8 SO
Ordering Information continued at end of data sheet.
__________Typical Operating Circuit
Q1
FZT749
+3.5V to +5V INPUT
3.3V @ 500mA
RB
12Ω
__________________Pin Configuration
TOP VIEW
BASE
BLIM
OUT
IN
IN 1
(ON) SHDN 2
PFO 3
MAX687
MAX688
MAX689
GND 4
( ) ARE FOR MAX687
DIP/SO/µMAX
8
CC
7
BASE
6
BLIM
5
OUT
PIN-PACKAGE
MAX687CPA
C2
68µF
C1
2.2µF
ON
MAX687
PFO
POWER-FAIL
OUTPUT
CC
ON
GND
GND
C3
10nF
________________________________________________________________ Maxim Integrated Products
Call toll free 1-800-998-8800 for free samples or literature.
1
MAX687/MAX688/MAX689
_______________General Description
The MAX687/MAX688/MAX689 low-dropout linear regulators operate with an input-to-output voltage differential limited 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 transistors (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 provides 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 applications include portable telephones and other battery-powered 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 shutdown-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, permitting the transition from normal mode to standby
mode to occur at a precise voltage level on SHDN.
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
ABSOLUTE MAXIMUM RATINGS
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
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.
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.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
11.0
V
LINEAR REGULATOR
Supply Voltage
VIN
(Note 1)
MAX687/MAX688
Output Voltage
VOUT
MAX689
Dropout Voltage (Note 2)
2.7
VIN = 3.8V, IBASE = 1mA
3.2
3.3
3.4
3.8V ≤ VIN ≤ 11.0V,
1µA ≤ IBASE ≤ 10mA
3.13
3.3
3.47
VIN = 3.5V, IBASE = 1mA
2.9
3.0
3.1
3.5V ≤ VIN ≤ 11.0V,
1µA ≤ IBASE ≤ 10mA
2.85
3.0
3.15
VIN - VOUT PNP = FZT749, ILOAD = 200mA, C2 = 20µF
40
MAX687/MAX688
0.4
1.4
MAX689
3.5V ≤ VIN ≤ 11.0V,
IBASE = 1mA
0.4
1.4
45
60
On
150
250
Standby,
MAX688/MAX689
11
25
mV/V
1µA ≤ IBASE ≤ 10mA
Load Regulation
Supply Current
IGND
VIN = 3.8V,
PNP = FZT749,
no load
BASE Sink Current
IBASE
VBASE = VIN - 1V
Shutdown
Base-Current Limit
RB is connected from BASE to BLIM (Ω),
RB = 0Ω to 100Ω
Start-Up Time
(Note 3)
10
2
< 0.02
1
20
40
PNP = FZT749, ILOAD = 100mA (Note 4)
µA
mA
mA
300
µs
2
C2
mV
70
100
130
RB + 5Ω RB + 5Ω RB + 5Ω
Start-Up Overshoot
Load Capacitance
mV
3.8V ≤ VIN ≤ 11.0V,
IBASE = 1mA
Line Regulation
V
10
_______________________________________________________________________________________
%
µF
High-Accuracy, Low-Dropout
Linear Regulators
(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.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
110
170
mV
7
mV
70
mV
MAX687: ON, PFO, SHDN
PFO Threshold Voltage Below
VNOM (Note 5)
VNOM VPFT
Falling VOUT, comparators monitor VOUT
PFO Hysteresis
Shutdown Threshold Voltage
Below VPFT
VPFT - VSD Falling VOUT, comparators monitor VOUT
Shutdown Threshold Voltage
VSD
Falling VOUT, comparators monitor VOUT
PFO Output Voltage High
VOH
ISOURCE = 50µA, part on, VIN = 2.7V
PFO Output Voltage Low
VOL
ISINK = 1.2mA, VIN = 2.7V
VIH
Output turns on
VIL
Output remains off
ON Threshold Voltage
20
2.96
V
VOUT - 0.3
V
0.06
0.3
V
1.0
V
0.2
ON Input Leakage Current
0.2
100
nA
MAX688/MAX689: SHDN, PFO
PFO Threshold Voltage
MAX688
3.07
3.13
3.19
MAX689
2.77
2.85
2.89
VPFT
Falling VOUT, comparators monitor VOUT
VSON
On, SHDN falling
1.25
VSSY
Standby
1.0
VSSD
Shutdown
PFO Hysteresis
7
SHDN Threshold Voltages
Rising SHDN, standby→on
V SHDN = 1.23V
PFO, SHDN Transient Rejection
Glitch immunity
100
ISINK = 1.2mA, VIN = 2.7V
0.06
PFO Off Leakage Current
Output Noise Voltage
70
-25
mV
25
V PFO = 11V, V SHDN > 1.25V
en
V
0.2
SHDN Input Current
VOL
mV
1.2
SHDN Hysteresis
PFO Output Voltage Low
V
10Hz ≤ f ≤ 10kHz, ILOAD = 200mA
66
10Hz ≤ f ≤ 1MHz, ILOAD = 200mA
105
nA
µs
0.3
V
1
µA
µVRMS
Note 1: Minimum VIN for regulated VOUT depends on the characteristics of the external PNP transistor, and on the load. The reference 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, VNOM, is defined under the default conditions of testing: VIN = 3.8V, IBASE = 1mA, TA = TMIN to TMAX.
_______________________________________________________________________________________
3
MAX687/MAX688/MAX689
ELECTRICAL CHARACTERISTICS (continued)
__________________________________________Typical Operating Characteristics
(Circuits of Figures 1 and 2, VIN = 5V, Q1 = FZT749, TA = +25°C, unless otherwise noted.)
3.31219
OUTPUT VOLTAGE (V)
3.30862
3.30505
3.30149
3.29792
3.29435
3.30800
3.30576
3.30352
3.30128
3.29904
3.29679
3.29455
3.29231
3.29007
3.28783
3.29078
3.28722
3.28365
50
100
150
NUMBER OF UNITS
200
50
100
150
NUMBER OF UNITS
250
Q1 = 2N2907
RB = 0Ω
0.9
0.10
0.6
0.5
0.4
0.3
0.2
OBSERVE MAXIMUM POWER
DISSIPATION LIMIT OF
EXTERNAL PASS TRANSISTOR.
600
1000
1400
MAX687/9-03
4
3
2
1
0
0
0
1800
200
600
400
1000
800
0
200
400
600
800
1000 1200
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
GND CURRENT vs. DROPOUT VOLTAGE
GND CURRENT vs. DROPOUT VOLTAGE
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
4
3
300mA LOAD
2
4
3
300mA LOAD
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
VIN - VOUT (V)
140
138
136
134
132
130
100mA LOAD
1
10mA LOAD
0
MAX687/9-9
142
5
2
100mA LOAD
144
SUPPLY CURRENT (µA)
5
6
GND CURRENT (mA)
6
146
MAX687/9-8
7
MAX687/9-7
7
250
0.1
0
200
200
6
GND CURRENT (mA)
0.15
150
5
0.7
0.20
100
GND CURRENT
vs. LOAD CURRENT
0.8
0
50
0
NUMBER OF UNITS
1.0
MAX687/9-05
Q1 = FZT749
RB = 0Ω
VIN - VOUT (V)
VIN - VOUT (V)
200
DROPOUT VOLTAGE
vs. LOAD CURRENT
0.30
0.05
3.00023
2.99848
2.99674
2.99150
2.98975
DROPOUT VOLTAGE
vs. LOAD CURRENT
0.25
3.00198
2.99499
2.99324
0
250
3.01071
3.00896
3.00721
3.00547
3.00372
MAX687/9-06
0
4
3.01595
3.01420
3.01245
MAX687/9-5
OUTPUT VOLTAGE (V)
3.31576
3.32145
3.31920
3.31696
3.31472
3.31248
3.31024
OUTPUT VOLTAGE (V)
3.31932
MAX687/9-01
MAX687/9-02
3.32289
1
MAX689
OUTPUT VOLTAGE DISTRIBUTION
MAX688
OUTPUT VOLTAGE DISTRIBUTION
MAX687
OUTPUT VOLTAGE DISTRIBUTION
GND CURRENT (mA)
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
128
10mA LOAD
126
0
0
1
2
3
4
5
VIN - VOUT (V)
6
7
8
-55
-25
0
25
50
75
TEMPERATURE (°C)
_______________________________________________________________________________________
100
125
High-Accuracy, Low-Dropout
Linear Regulators
3.310
0.1500
0.1000
3.305
3.300
3.295
3.290
0.0500
3.285
0
3.280
VIN = 4.3V Min
ILOAD = 20mA
70
RIPPLE REJECTION (dB)
0.2000
80
MAX687/9-11
MAX687/9-10
0.2500
MAX687/MAX688
RIPPLE REJECTION vs. FREQUENCY
3.315
OUTPUT VOLTAGE (V)
SHUTDOWN SUPPLY CURRENT (µA)
0.3000
OUTPUT VOLTAGE
vs. TEMPERATURE
MAX687/9-16
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
60
VIN = 3.6V Min
ILOAD = 200mA
50
40
30
20
10
C2 = 20µF
-55
-25
0
25
50
75
100
125
0
-55
-25
TEMPERATURE (°C)
0
25
50
75
TEMPERATURE (°C)
100
VIN
3.6V
100k
VIN
5V/div
VOUT
1V/div
VIN
3.4V
ILOAD = 200mA
C1 = 2.2µF
C2 = 20µF
C3 = 10nF
2ms/div
SHDN
5V/div
ILOAD = 500mA
C1 = 2.2µF
C2 = 68µF
C3 = 10nF
LOAD-TRANSIENT RESPONSE
1ms/div
LOAD-TRANSIENT RESPONSE
VOUT
3.3V
10mV/div
VOUT
3.3V
10mV/div
500mA
500mA
ILOAD
200mA/div
ILOAD
200mA/div
0mA
100µs/div
1k
10k
FREQUENCY (Hz)
VIN
3.6V
VIN
3.4V
VIN = 3.4V
100
VOUT
3.3V
1mV/div
VOUT
3.3V
1mV/div
2ms/div
10
MAX687/MAX688
POWER-UP AND EXIT FROM SHUTDOWN
LINE-TRANSIENT RESPONSE
LINE-TRANSIENT RESPONSE
ILOAD = 70mA
C1 = 2.2µF
C2 = 20µF
C3 = 10nF
125
0mA
VIN = 3.5V
100µs/div
_______________________________________________________________________________________
5
MAX687/MAX688/MAX689
____________________________Typical Operating Characteristics (continued)
(Circuits of Figures 1 and 2, VIN = 5V, Q1 = FZT749, TA = +25°C, unless otherwise noted.)
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
______________________________________________________________Pin Description
PIN
NAME
1
IN
FUNCTION
Positive input voltage, 2.7V to 11.0V
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.
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 function 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.
4
GND
Ground
5
OUT
Regulator Output. MAX687/MAX688, 3.3V; MAX689, 3.0V.
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 provides 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
2
Compensation Capacitor. Connect a non-polarized capacitor (10nF to 100nF) from CC to GND.
_______________Detailed Description
The MAX687/MAX688/MAX689 are precision lowdropout linear regulators employing external PNP transistors 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 voltages), 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).
6
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
The MAX687’s output voltage is internally monitored; a
falling VOUT is signaled by PFO going low. As the output falls further, the MAX687 automatically enters a lowpower 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
_______________________________________________________________________________________
High-Accuracy, Low-Dropout
Linear Regulators
Q1 FZT749
+5V INPUT
3.3V @ 500mA
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 resistive 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 current gain (hFE). With RB = 12Ω, BLIM limits base current to 6mA (IBASE = 0.1V / (RB + 5Ω)). See BaseCurrent 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 PFO output’s noise sensitivity, and stops the MAX687 from being shut down inadvertently 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 circuit can deliver. The largest guaranteed output current
+5V INPUT
RB 12Ω
BASE
C4
0.1µF
BASE
OUT
POWER FAIL
PFO
ON
CC
GND
C3
10nF
C1
2.2µF
ON / OFF
R2
100k
BLIM
OUT
IN
C2
68µF
MAX687
C1
2.2µF
R1
10kΩ
RB 12Ω
BLIM
IN
3.3V/ 3.0V @ 500mA
Q1 FZT749
MAX688
MAX689
SHDN
GND
C2
68µF
PFO
POWER FAIL
CC
C3
10nF
GND
ON CAN BE DRIVEN DIRECTLY FROM LOGIC WHEN R1 AND C4 ARE NOT USED.
Figure 1. MAX687 Operating Circuit
GND
Figure 2. MAX688/MAX689 Operating Circuit
_______________________________________________________________________________________
7
MAX687/MAX688/MAX689
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 prevent deep discharge of a battery, for example, to provide “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 V OUT 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-current 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.
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
is given by ILOAD(MAX) = 10mA x hFE(MIN). The transistor’s rated power dissipation must exceed the actual
power dissipated in the transistor. The power dissipated (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 transistor 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 5Ω resistor in series with the
external resistance. Choose the base-current-limiting
resistor, R B , so the drop across it at rated load is
approximately 50mV.
RB =
(50mV) x hFE(MIN)
ILOAD(MAX)
− 5Ω
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 voltage. 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.
8
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 stability 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 temperatures 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 capacitors (e.g., ceramic, polyester, etc.) to keep leakage currents 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 nominal VOUT at IBASE = 1mA. PFO sources and sinks current 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.
_______________________________________________________________________________________
High-Accuracy, Low-Dropout
Linear Regulators
DROPOUT VOLTAGE vs. LOAD CURRENT
High-Power Output Circuit
MAX687/9-04
1.0
Q1 = TIP42
Q2 = 2N4403
BASE = BLIM
0.9
0.8
VIN - VOUT (V)
Figure 3 shows a pseudo-Darlington transistor configuration 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
__________Applications Information
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
1000
2000
3000
4000
LOAD CURRENT (mA)
Q1
T1P42
+5V INPUT
3.3V/ 3.0V @ 4A
Q2
2N4403
LOAD-TRANSIENT RESPONSE
1kΩ
10Ω
BASE
IN
C1
220µF
ON / OFF
Figure 4. Dropout Voltage vs. Load Current of Figure 3
C2
470µF
x3
MAX688
MAX689
SHDN
GND
VOUT
+3.3V, 20mV/div
R2
100kΩ
BLIM
OUT
PFO
IOUT
1A/div
POWER FAIL
CC
C3
10nF
50µs/div
Figure 3. 4A Low-Dropout Circuit
Figure 5. Transient Response for a 200mA to 4A Load Step
Using Circuit of Figure 3
_______________________________________________________________________________________
9
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
Table 2a. Component Suppliers
DEVICE
MANUFACTURER
PRODUCTION
METHOD
CAPACITORS
267 series
Matsuo
F95 Tantalum series Nichicon
Surface Mount
Table 2b. Manufacturers’ Phone
and Fax Numbers
MANUFACTURER
COUNTRY
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
USA
(708) 843-7500 (708) 843-2798
TELEPHONE
FAX
595 Tantalum series Sprague
OS-CON series
low-ESR organic
semiconductor
Sanyo
LXF series
United Chemi-Con
Through-Hole
Nichicon
Japan
BIPOLAR TRANSISTORS
ZTX749
Zetex
T1P42
Motorola
2N4403
Motorola
USA
Sanyo
Japan
Through-Hole
2N2907A
Motorola
CMPT2907A
Central Semiconductor
PZT2907AT1
Motorola
FZT749
Zetex
10
Surface Mount
+81-7-52318461
+81-7-52564158
(619) 661-6835 (619) 661-1055
+81-7-20706306
+81-7-20701174
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
+44-61-6275105
______________________________________________________________________________________
+44-61-6275467
High-Accuracy, Low-Dropout
Linear Regulators
PART
TEMP. RANGE
MAX687/MAX688/MAX689
_Ordering Information (continued)
PIN-PACKAGE
MAX688CPA
0°C to +70°C
8 Plastic DIP
MAX688CSA
MAX688CUA
MAX688EPA
MAX688ESA
MAX689CPA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
0°C to +70°C
8 SO
8 µMAX
8 Plastic DIP
8 SO
8 Plastic DIP
MAX689CSA
MAX689CUA
MAX689EPA
MAX689ESA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
8 SO
8 µMAX
8 Plastic DIP
8 SO
______________________________________________________________________________________
11
MAX687/MAX688/MAX689
High-Accuracy, Low-Dropout
Linear Regulators
________________________________________________________Package Information
DIM
C
α
A
0.101mm
0.004 in
e
B
A1
E
L
A
A1
B
C
D
E
e
H
L
α
INCHES
MAX
MIN
0.044
0.036
0.008
0.004
0.014
0.010
0.007
0.005
0.120
0.116
0.120
0.116
0.0256
0.198
0.188
0.026
0.016
6°
0°
MILLIMETERS
MIN
MAX
0.91
1.11
0.10
0.20
0.25
0.36
0.13
0.18
2.95
3.05
2.95
3.05
0.65
4.78
5.03
0.41
0.66
0°
6°
H
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.