MAX689CPA [MAXIM]
High-Accuracy, Low-Dropout Linear Regulators; 高精度，低压差线性稳压器
| 型号： | MAX689CPA |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | High-Accuracy, Low-Dropout Linear Regulators |
| 文件： | 总12页 (文件大小：105K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-0329; Rev 0; 12/94
Hig h -Ac c u ra c y, Lo w -Dro p o u t
Lin e a r Re g u la t o rs
7/MAX689
_______________Ge n e ra l De s c rip t io n
____________________________Fe a t u re s
♦ Fixed Outputs:
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.
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
The 3.3V MAX687 automatically shuts down whenever
the outp ut volta g e d rop s b e low 2.96V. An inte rna l
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-
e re d e q uip me nt whe re the p owe r s up p ly mus t b e
disabled when the battery voltage is low.
♦ 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%
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.
______________Ord e rin g In fo rm a t io n
PART
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
8 Plastic DIP
8 SO
MAX687CPA
MAX687CSA
MAX687CUA
MAX687EPA
MAX687ESA
8 µMAX
8 Plastic DIP
8 SO
________________________Ap p lic a t io n s
High-Efficiency Linear Regulator
Battery-Powered Devices
Ordering Information continued at end of data sheet.
__________Typ ic a l Op e ra t in g Circ u it
Portable Instruments
Portable Telephones
Power Supply or Backup Supply for Memory
Q1
FZT749
+3.5V to +5V INPUT
3.3V @ 500mA
R
B
__________________P in Co n fig u ra t io n
12Ω
TOP VIEW
BASE
BLIM
OUT
IN
IN
1
2
3
4
8
7
6
5
CC
C2
68µF
C1
2.2µF
POWER-FAIL
OUTPUT
(ON) SHDN
PFO
BASE
BLIM
OUT
PFO
CC
MAX687
GND
MAX687
MAX688
MAX689
ON
ON
GND
C3
10nF
GND
(
) ARE FOR MAX687
DIP/SO/µMAX
________________________________________________________________ Maxim Integrated Products
1
Ca ll t o ll fre e 1 -8 0 0 -9 9 8 -8 8 0 0 fo r fre e s a m p le s o r lit e ra t u re .
Hig h -Ac c u ra c y, Lo w -Dro p o u t
Lin e a r Re g u la t o rs
ABSOLUTE MAXIMUM RATINGS
Input Supply Voltage IN to GND ............................................12V
Continuous Power Dissipation (T = +70°C)
A
Terminal Voltages to GND
PFO (MAX687)........................................-0.3V to V
PFO (MAX688/MAX689) ......................................-0.3V to 12V
All Remaining Pins .....................................-0.3V to V + 0.3V
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
+ 0.3V
OUT
IN
PFO Sink Current ...............................................................10mA
PFO Source Current (MAX687)...........................................10mA
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
(V = 3.8V, SHDN = V (MAX688/MAX689), R = 0Ω, C1 = 2.2µF, C2 = 10µF, C3 = 10nF, T = T
to T , unless otherwise
MAX
IN
IN
B
A
MIN
noted. Typical values are at T = +25°C.)
A
PARAMETER
LINEAR REGULATOR
Supply Voltage
SYMBOL
CONDITIONS
MIN
TYP
MAX UNITS
V
IN
(Note 1)
2.7
3.2
11.0
3.4
V
V
IN
= 3.8V, I
= 1mA
3.3
3.3
3.0
3.0
40
BASE
MAX687/MAX688
3.8V ≤ V ≤ 11.0V,
IN
3.13
2.9
3.47
3.1
7/MAX689
1µA ≤ I
≤ 10mA
BASE
Output Voltage
V
OUT
V
V
IN
= 3.5V, I
= 1mA
BASE
MAX689
3.5V ≤ V ≤ 11.0V,
1µA ≤ I
IN
2.85
3.15
≤ 10mA
BASE
Dropout Voltage (Note 2)
Line Regulation
V
IN
- V
OUT
PNP = FZT749, I = 200mA, C2 = 20µF
LOAD
mV
mV/V
mV
3.8V ≤ V ≤ 11.0V,
IN
MAX687/MAX688
MAX689
0.4
1.4
1.4
I
= 1mA
BASE
3.5V ≤ V ≤ 11.0V,
IN
0.4
I
= 1mA
BASE
Load Regulation
1µA ≤ I
≤ 10mA
45
60
BASE
On
150
250
V
= 3.8V,
IN
Standby,
MAX688/MAX689
Supply Current
I
PNP = FZT749,
no load
11
25
µA
GND
Shutdown
< 0.02
20
1
BASE Sink Current
Base-Current Limit
I
V
= V - 1V
10
70
40
mA
mA
BASE
BASE
IN
100
130
R
R
is connected from BASE to BLIM (Ω),
= 0Ω to 100Ω
B
B
R
B
+ 5Ω R + 5Ω R + 5Ω
B B
Start-Up Time
(Note 3)
300
µs
%
Start-Up Overshoot
Load Capacitance
2
C2
PNP = FZT749, I
= 100mA (Note 4)
10
µF
LOAD
2
_______________________________________________________________________________________
Hig h -Ac c u ra c y, Lo w -Dro p o u t
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7/MAX689
ELECTRICAL CHARACTERISTICS (continued)
(V = 3.8V, SHDN = V (MAX688/MAX689), R = 0Ω, C1 = 2.2µF, C2 = 10µF, C3 = 10nF, T = T
to T , unless otherwise
MAX
IN
IN
B
A
MIN
noted. Typical values are at T = +25°C.)
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX UNITS
MAX687: ON, PFO, SHDN
PFO Threshold Voltage Below
V
V
PFT
-
NOM
Falling V
, comparators monitor V
110
170
7
mV
mV
mV
OUT
OUT
V
NOM
(Note 5)
PFO Hysteresis
Shutdown Threshold Voltage
V
- V
SD
Falling V
, comparators monitor V
OUT
20
70
PFT
OUT
Below V
PFT
Shutdown Threshold Voltage
PFO Output Voltage High
PFO Output Voltage Low
V
Falling V
, comparators monitor V
OUT
2.96
V
V
SD
OUT
V
OH
I
= 50µA, part on, V = 2.7V
V
- 0.3
SOURCE
IN
OUT
V
OL
I
= 1.2mA, V = 2.7V
0.06
0.2
0.3
V
SINK
IN
V
Output turns on
1.0
IH
ON Threshold Voltage
V
V
Output remains off
0.2
IL
ON Input Leakage Current
100
nA
MAX688/MAX689: SHDN, PFO
MAX688
MAX689
3.07
2.77
3.13
2.85
7
3.19
2.89
Falling V
parators monitor V
, com-
OUT
PFO Threshold Voltage
PFO Hysteresis
V
PFT
V
OUT
mV
V
On, SHDN falling
Standby
1.25
1.0
SON
SHDN Threshold Voltages
V
1.2
0.2
V
SSY
V
SSD
Shutdown
Rising SHDN, standby→on
= 1.23V
SHDN Hysteresis
70
mV
nA
µs
SHDN Input Current
V
-25
25
SHDN
PFO, SHDN Transient Rejection
PFO Output Voltage Low
PFO Off Leakage Current
Glitch immunity
= 1.2mA, V = 2.7V
100
V
OL
I
0.06
0.3
1
V
SINK
IN
V
= 11V, V
> 1.25V
SHDN
µA
PFO
10Hz ≤ f ≤ 10kHz, I
= 200mA
66
LOAD
LOAD
Output Noise Voltage
e
µV
RMS
n
10Hz ≤ f ≤ 1MHz, I
= 200mA
105
Note 1: Minimum V for regulated V
depends on the characteristics of the external PNP transistor, and on the load. The refer-
IN
OUT
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 V - V when V is 50mV below its value at V = V + 1V.
IN
OUT
OUT
IN
NOM
Note 3: The start-up time specification is the time taken from ON or SHDN rising to BASE sinking current. V
rise time is longer
OUT
and is a function of load capacitance, C2, and load resistance, R .
L
Note 4: Minimum load capacitance is a function of R . Minimum C2 = 10µF for loads up to 100mA and 1µF/10mA for higher loads.
L
ESR of C2 should be no larger than 1/100 of R . Guaranteed by design.
L
Note 5: The nominal output voltage, V
, is defined under the default conditions of testing: V = 3.8V, I
= 1mA, T = T
to T
.
NOM
IN
BASE
A
MIN
MAX
_______________________________________________________________________________________
3
Hig h -Ac c u ra c y, Lo w -Dro p o u t
Lin e a r Re g u la t o rs
__________________________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s
(Circuits of Figures 1 and 2, V = 5V, Q1 = FZT749, T = +25°C, unless otherwise noted.)
IN
A
MAX689
OUTPUT VOLTAGE DISTRIBUTION
MAX688
OUTPUT VOLTAGE DISTRIBUTION
MAX687
OUTPUT VOLTAGE DISTRIBUTION
3.32145
3.31920
3.31696
3.31472
3.31248
3.31024
3.01595
3.01420
3.01245
3.01071
3.00896
3.00721
3.00547
3.00372
3.32289
3.31932
3.31576
3.31219
3.30862
3.30505
3.30800
3.30576
3.30352
3.00198
3.00023
2.99848
2.99674
2.99499
2.99324
2.99150
2.98975
3.30149
3.29792
3.30128
3.29904
3.29679
3.29455
3.29231
3.29007
3.28783
3.29435
3.29078
3.28722
3.28365
0
50
100
150
200
250
0
50
100
150
200
250
0
50
100
150
200
250
NUMBER OF UNITS
NUMBER OF UNITS
NUMBER OF UNITS
DROPOUT VOLTAGE
vs. LOAD CURRENT
DROPOUT VOLTAGE
vs. LOAD CURRENT
GND CURRENT
vs. LOAD CURRENT
1.0
0.30
0.25
0.20
0.15
0.10
0.05
0
6
5
4
3
2
1
Q1 = 2N2907
B
Q1 = FZT749
B
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
R = 0Ω
R = 0Ω
7/MAX689
OBSERVE MAXIMUM POWER
DISSIPATION LIMIT OF
EXTERNAL PASS TRANSISTOR.
0
0
0
200
400
600
800
1000
0
200
600
1000
1400
1800
200
400
600
800 1000 1200
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
GND CURRENT vs. DROPOUT VOLTAGE
GND CURRENT vs. DROPOUT VOLTAGE
7
6
146
7
6
144
142
140
138
136
134
132
130
128
126
5
4
5
4
3
2
1
3
2
1
300mA LOAD
300mA LOAD
100mA LOAD
10mA LOAD
100mA LOAD
10mA LOAD
0
0
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
- V (V)
-55 -25
0
25
50
75 100 125
0
1
2
3
4
5
6
7
8
V
TEMPERATURE (°C)
IN OUT
V
- V (V)
IN OUT
4
_______________________________________________________________________________________
Hig h -Ac c u ra c y, Lo w -Dro p o u t
Lin e a r Re g u la t o rs
7/MAX689
____________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(Circuits of Figures 1 and 2, V = 5V, Q1 = FZT749, T = +25°C, unless otherwise noted.)
IN
A
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
OUTPUT VOLTAGE
vs. TEMPERATURE
MAX687/MAX688
RIPPLE REJECTION vs. FREQUENCY
0.3000
0.2500
0.2000
0.1500
3.315
3.310
80
70
V
= 4.3V Min
= 20mA
IN
I
LOAD
60
50
40
3.305
3.300
3.295
3.290
3.285
V
= 3.6V Min
= 200mA
IN
I
LOAD
30
20
0.1000
0.0500
0
10
0
C2 = 20µF
100
3.280
-55 -25
0
25
50
75 100 125
-55 -25
0
25
50
75 100 125
10
1k
10k
100k
FREQUENCY (Hz)
TEMPERATURE (°C)
TEMPERATURE (°C)
MAX687/MAX688
LINE-TRANSIENT RESPONSE
POWER-UP AND EXIT FROM SHUTDOWN
LINE-TRANSIENT RESPONSE
V
IN
5V/div
V
3.3V
OUT
V
OUT
3.3V
1mV/div
1mV/div
V
OUT
1V/div
V
IN
V
IN
3.6V
3.6V
V
IN
3.4V
SHDN
5V/div
V
3.4V
IN
2ms/div
1ms/div
2ms/div
I
= 200mA
LOAD
I
= 500mA
I
= 70mA
LOAD
LOAD
C1 = 2.2µF
C2 = 20µF
C3 = 10nF
C1 = 2.2µF
C2 = 68µF
C3 = 10nF
C1 = 2.2µF
C2 = 20µF
C3 = 10nF
LOAD-TRANSIENT RESPONSE
LOAD-TRANSIENT RESPONSE
V
3.3V
OUT
V
OUT
3.3V
10mV/div
10mV/div
500mA
500mA
I
I
LOAD
LOAD
200mA/div
200mA/div
0mA
0mA
100µs/div
100µs/div
V
IN
= 3.4V
V = 3.5V
IN
_______________________________________________________________________________________
5
Hig h -Ac c u ra c y, Lo w -Dro p o u t
Lin e a r Re g u la t o rs
______________________________________________________________P in De s c rip t io n
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 V exceeds the internal shutdown threshold voltage. The MAX687 is shut down when V < 2.96V,
OUT
OUT
(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 V if not used.
IN
2
SHDN is a three-level input that controls the mode of operation. The device is on when V
The output is disabled and the supply current is reduced (I < 25µA, standby mode) when V
> 1.25V.
< 1.2V,
SHDN
SHDN
SHDN
(MAX688/
MAX689)
IN
and is fully off (I < 1µA, shutdown mode) when V
< 0.2V. Connect SHDN to IN if the shutdown func-
SHDN
IN
tion is not used. PFO is low when SHDN is low (below 0.2V).
Power-Fail Output. PFO trips when V is 170mV below nominal V
at I = 1mA. PFO sources and
BASE
OUT
OUT
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
5
GND
OUT
Ground
Regulator Output. MAX687/MAX688, 3.3V; MAX689, 3.0V.
Base current limit. A resistor (R ) connected between BASE and BLIM sets the maximum base drive to the
B
PNP transistor: I
≤ 0.1V / (R + 5Ω). This limits quiescent current rise during dropout and also pro-
B
BASE
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 (h ) is
FE
controlled. Connect to BASE if not used.
7/MAX689
Base drive for the external PNP transistor. Current limiting is controlled using a resistor (R ) connected
B
between BASE and BLIM. For maximum output current, connect BASE to BLIM.
7
8
BASE
CC
Compensation Capacitor. Connect a non-polarized capacitor (10nF to 100nF) from CC to GND.
_______________De t a ile d De s c rip t io n
Table 1. Device Functions
The MAX687/MAX688/MAX689 a re p re c is ion 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
FUNCTION
MAX687
MAX688
MAX689
V
OUT
3.3V
3.3V
3.0V
Automatic at low
Shutdown
Control
External
SHDN
External
SHDN
V . Latched.
OUT
Use ON to start.
PFO
Sources & Sinks
Open Drain
Open Drain
The MAX687’s output voltage is internally monitored; a
falling V is signaled by PFO going low. As the out-
V
. The Power-Fail Output (PFO) goes low when
CE(SAT)
OUT
the output voltage drops 170mV below the nominal
level.
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
The three devices differ in their output voltages, in their
shutdown-control functions, and in PFO’s output drive
(see Table 1).
110mV below the nominal V , and shutdown occurs
OUT
by 2.96V. PFO is guaranteed to trip before the device
6
_______________________________________________________________________________________
Hig h -Ac c u ra c y, Lo w -Dro p o u t
Lin e a r Re g u la t o rs
7/MAX689
shuts down. Once the MAX687 is shut down, it can
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-
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.
tive divider from V
.
When V
is less than 1.2V,
IN
SHDN
the output is off. The device is fully shut down (<1µA)
whe n SHDN is p ulle d b e low 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 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
The accuracy of the output current limit depends on
accurate knowledge of the PNP pass transistor’s cur-
rent gain (h ). With R = 12Ω, BLIM limits base cur-
FE
B
rent to 6mA (I
= 0.1V / (R + 5Ω)). See Base-
BASE
B
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 PFO output’s noise sen-
sitivity, and stops the MAX687 from being shut down inad-
vertently when there is noise on the input supply.
for high-power circuits (I
> 3A), increase the value
LOAD
of R1 to increase the ON pulse width.
_______________Tra n s is t o r S e le c t io n
The 3.3V MAX688 and the 3.0V MAX689 incorporate
the s a me PFO wa rning whe ne ve r V
S p e c ific a t io n s
The PNP pass transistor must meet specifications for
d roop s .
OUT
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.
• current gain,
• power dissipation, and
• collector current.
The h influences the maximum output current the cir-
FE
cuit can deliver. The largest guaranteed output current
3.3V/ 3.0V @ 500mA
Q1 FZT749
+5V INPUT
Q1 FZT749
3.3V @ 500mA
+5V INPUT
R
B
12Ω
R
B
12Ω
R2
100k
BASE
IN
BLIM
OUT
BASE
IN
BLIM
OUT
C4
0.1µF
C2
68µF
C2
68µF
C1
2.2µF
MAX687
POWER FAIL
C1
2.2µF
MAX688
MAX689
PFO
CC
PFO
CC
POWER FAIL
ON
ON / OFF
SHDN
GND
C3
10nF
GND
R1
10kΩ
C3
10nF
GND
GND
ON CAN BE DRIVEN DIRECTLY FROM LOGIC WHEN R1 AND C4 ARE NOT USED.
Figure 1. MAX687 Operating Circuit
Figure 2. MAX688/MAX689 Operating Circuit
_______________________________________________________________________________________
7
Hig h -Ac c u ra c y, Lo w -Dro p o u t
Lin e a r Re g u la t o rs
is given by I
= 10mA x h
.
FE(MIN)
The tran-
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.
LOAD(MAX)
sistor’s rated power dissipation must exceed the actual
power dissipated in the transistor. The power dissipat-
ed (PD) equals the maximum load current (I
)
LOAD(MAX)
times the maximum input to output voltage differential:
PD = I x (V - V ). The rated tran-
sistor collector current must exceed the maximum load
current. Suitable transistors include the Zetex FZT749,
and the 2N2907A (see Table 2).
Ou t p u t Ca p a c it o r (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.
LOAD(MAX)
IN(MAX)
OUT
Ba s e -Cu rre n t Lim it in g
A comparator monitors the voltage across the external
b a s e -c urre nt-limiting re s is tor (b e twe e n BASE a nd
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
Co m p e n s a t io n Ca p a c it o r (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
p owe r-on ove rs hoot, b ut e xte nd p owe r-up time s .
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.
re s is tor, R , s o the d rop a c ros s it a t ra te d loa d is
B
approximately 50mV.
50mV x h
(
)
FE(MIN)
R
=
− 5Ω
B
I
LOAD(MAX)
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 R + 5Ω, base-current drive
B
7/MAX689
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 h
within reasonable limits, base-current control effectively
limits output current without a dropout voltage penalty.
is defined
__________________P o w e r-Fa il Ou t p u t
FE
The PFO output trips when V
is 170mV below nomi-
OUT
nal V
at I
= 1mA. PFO sources and sinks cur-
OUT
BASE
re nt in the MAX687, b ut is a n op e n d ra in 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.
________________Ca p a c it o r S e le c t io n
Byp a s s Ca p a c it o r (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
_______________________________________________________________________________________
Hig h -Ac c u ra c y, Lo w -Dro p o u t
Lin e a r Re g u la t o rs
7/MAX689
__________Ap p lic a t io n s In fo rm a t io n
DROPOUT VOLTAGE vs. LOAD CURRENT
Hig h -P o w e r Ou t p u t Circ u it
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.
1.0
Q1 = TIP42
Q2 = 2N4403
BASE = BLIM
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Figure 4 shows the (V - V
) voltage required to
OUT
IN
maintain regulation for different load currents. Figure 5
shows an oscilloscope plot of the transient response of
a 200mA to 4A load step.
0
1000
2000
3000
4000
LOAD CURRENT (mA)
Figure 4. Dropout Voltage vs. Load Current of Figure 3
Q1
T1P42
+5V INPUT
3.3V/ 3.0V @ 4A
Q2
2N4403
LOAD-TRANSIENT RESPONSE
1kΩ
10Ω
V
OUT
+3.3V, 20mV/div
R2
100kΩ
BASE
IN
BLIM
OUT
C2
470µF
x3
C1
220µF
MAX688
MAX689
SHDN
PFO
I
ON / OFF
OUT
1A/div
POWER FAIL
GND
CC
C3
10nF
50µs/div
Figure 5. Transient Response for a 200mA to 4A Load Step
Using Circuit of Figure 3
Figure 3. 4A Low-Dropout Circuit
_______________________________________________________________________________________
9
Hig h -Ac c u ra c y, Lo w -Dro p o u t
Lin e a r Re g u la t o rs
Table 2a. Component Suppliers
Table 2b. Manufacturers’ Phone
and Fax Numbers
PRODUCTION
METHOD
DEVICE
MANUFACTURER
MANU-
COUNTRY TELEPHONE
FAX
FACTURER
CAPACITORS
Central
Semiconductor
267 series
Matsuo
USA
(516) 435-1110 (516) 435-1824
F95 Tantalum series Nichicon
595 Tantalum series Sprague
OS-CON series
Surface Mount
Through-Hole
Matsuo
USA
USA
(714) 969-2491 (714) 960-6492
(602) 244-3370 (602) 244-4015
Motorola
low-ESR organic
semiconductor
Sanyo
USA
Japan
USA
(708) 843-7500 (708) 843-2798
Nichicon
+81-7-5231-
8461
+81-7-5256-
4158
LXF series
United Chemi-Con
BIPOLAR TRANSISTORS
(619) 661-6835 (619) 661-1055
Sanyo
ZTX749
Zetex
+81-7-2070-
6306
+81-7-2070-
1174
Japan
USA
T1P42
Motorola
Through-Hole
Surface Mount
Sprague
(603) 224-1961 (603) 224-1430
2N4403
Motorola
United
Chemi-Con
USA
(714) 255-9500 (714) 255-9400
2N2907A
CMPT2907A
PZT2907AT1
FZT749
Motorola
Central Semiconductor
Motorola
USA
UK
(516) 543-7100 (516) 864-7630
Zetex
+44-61-627-
5105
+44-61-627-
5467
7/MAX689
Zetex
10 ______________________________________________________________________________________
Hig h -Ac c u ra c y, Lo w -Dro p o u t
Lin e a r Re g u la t o rs
7/MAX689
_Ord e rin g In fo rm a t io n (c o n t in u e d )
PART
TEMP. RANGE
0°C to +70°C
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
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
MAX688CPA
MAX688CSA
MAX688CUA
MAX688EPA
MAX688ESA
MAX689CPA
MAX689CSA
MAX689CUA
MAX689EPA
MAX689ESA
8 Plastic DIP
8 SO
8 µMAX
8 Plastic DIP
8 SO
8 Plastic DIP
8 SO
8 µMAX
8 Plastic DIP
8 SO
______________________________________________________________________________________ 11
Hig h -Ac c u ra c y, Lo w -Dro p o u t
Lin e a r Re g u la t o rs
________________________________________________________P a c k a g e In fo rm a t io n
INCHES
MILLIMETERS
DIM
MIN
0.036
MAX
0.044
0.008
0.014
0.007
0.120
0.120
MIN
0.91
0.10
0.25
0.13
2.95
2.95
MAX
1.11
0.20
0.36
0.18
3.05
3.05
A
C
A1 0.004
α
A
B
C
D
E
e
0.010
0.005
0.116
0.116
0.101mm
0.004 in
e
B
A1
L
0.0256
0.65
H
L
0.188
0.016
0°
0.198
0.026
6°
4.78
0.41
0°
5.03
0.66
6°
α
E
H
8-PIN µMAX
MICROMAX SMALL OUTLINE
PACKAGE
7/MAX689
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 __________________Ma x im In t e g ra t e d P ro d u c t s , 1 2 0 S a n Ga b rie l Drive , S u n n yva le , CA 9 4 0 8 6 (4 0 8 ) 7 3 7 -7 6 0 0
© 1994 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
相关型号：
MAX689EVKIT
1Msps.µ.P Compatible.8-Bit ADC with 1µ.A Power Down[MAX153/MAX153C/D/MAX153CAP/MAX153CAP-T/MAX153CPP/MAX153CWP/MAX153CWP-T/MAX153EAP/MAX153EAP-T/MAX153EPP/MAX153EWP/MAX153EWP-T/MAX153MJP]
MAXIM
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