Application Notes
The CS5208-1 linear regulator has a composite PNP-NPN
output stage that requires an output capacitor for stability.
A detailed procedure for selecting this capacitor is includ-
ed in the Stability Considerations section.
Design Guidelines
This LDO adjustable regulator has an output voltage range
of 1.25V to 4.5V. An external resistor divider sets the out-
put voltage as shown in Figure 1. The regulator’s voltage
sensing error amplifier maintains a fixed 1.25V reference
between the output pin and the adjust pin.
A resistor divider network R1 and R2 causes a fixed current
to flow to ground. This current creates a voltage across R2
that adds to the 1.25V across R1 and sets the overall output
voltage. The adjust pin current (typically 50A) also flows
through R2 and adds a small error that should be taken
into account if precise adjustment of Vout is necessary. The
output voltage is set according to the formula:
VOUT = VREF ×
+ R2 × IAdj
The term IAdj × R2 represents the error added by the adjust
pin current.
R1 is chosen so that the minimum load current is a least
10mA. R1 and R2 should be of the same composition for
best tracking over temperature. The divider resistors
should be placed as close to the IC as possible and connect-
ed to the output with a separate metal trace.
R1 + R2
R1
Adjustable Operation
Theory of Operation
CS5208-1
4
20.0
18.0
16.0
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Output
Current
(A)
VIN-VOUT (V)
4.0
4.5
5.0
5.5
Dropout
V
oltage
(V)
Output Current (A)
0.00
0.25
0.50
0.75
1.00
1.25
0.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
8.0
1.00
2.00
3.00
4.00
5.00
Minimum
Load
Current
(mA)
VIN – VOUT (V)
0.80
0.82
0.88
0.90
0.98
1.00
TCASE = 23°C
0.84
0.86
0.92
0.94
0.96
TCASE = 125°C
TCASE = 0°C
Typical Performance Characteristics: continued
Dropout Voltage vs. Output Current
Short Circuit Current vs. VIN - VOUT
Minimum Load Current vs. VIN - VOUT
10
1
10
2
10
3
10
4
10
5
20.0
30.0
50.0
70.0
90.0
Frequency (Hz)
Ripple
Rejection
(dB)
80.0
60.0
40.0
10.0
V
IN - VOUT = 2V
V
Ripple = 1VPP
IOUT = 4A
C
Adj = 0.1F
C
OUT = 22F
10
6
Ripple Rejection vs. Frequency