MAX687-MAX689 MAXIM [Maxim Integrated Products], MAX687-MAX689 Datasheet - Page 9

• Manufacturer Part Number: MAX687-MAX689
• Description: High-Accuracy, Low-Dropout Linear Regulators
• Manufacturer: MAXIM [Maxim Integrated Products]

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 (V
maintain regulation for different load currents. Figure 5
shows an oscilloscope plot of the transient response of
a 200mA to 4A load step.
Figure 3. 4A Low-Dropout Circuit
__________Applications Information
ON / OFF
+5V INPUT
C1
220 F
1k
T1P42
Q1
_______________________________________________________________________________________
IN
SHDN
2N4403
BASE
Q2
High-Power Output Circuit
GND
IN
MAX688
MAX689
- V
OUT
10
CC
BLIM
OUT
PFO
) voltage required to
C3
10nF
3.3V/ 3.0V @ 4A
C2
470 F
x3
POWER FAIL
High-Accuracy, Low-Dropout
R2
100k
Figure 4. Dropout Voltage vs. Load Current of Figure 3
Figure 5. Transient Response for a 200mA to 4A Load Step
Using Circuit of Figure 3
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Linear Regulators
0
DROPOUT VOLTAGE vs. LOAD CURRENT
Q1 = TIP42
Q2 = 2N4403
BASE = BLIM
LOAD-TRANSIENT RESPONSE
1000
LOAD CURRENT (mA)
50 s/div
2000
3000
4000
V
+3.3V, 20mV/div
I
1A/div
OUT
OUT
9