CS5203A−1, CS5203A−2, CS5203A−3, CS5203A−5
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5
Frequency (Hz)
Figure 9. Ripple Rejection vs. Frequency
(Adjustable Versions)
Ripple Rejection (dB)
10
1
100
90
80
70
60
50
40
30
20
10
0
10
2
10
3
10
4
10
5
T
CASE
= 25°C
I
OUT
= 3.0 A
(V
IN
− V
OUT
) = 3.0 V
V
RIPPLE
= 1.6 V
PP
C
Adj
= 25 F
APPLICATIONS INFORMATION
The CS5203A family of linear regulators provides fixed
or adjustable voltages at currents up to 3.0 A. The regulators
are protected against short circuit, and include thermal
shutdown and safe area protection (SOA) circuitry. The
SOA protection circuitry decreases the maximum available
output current as the input−output differential voltage
increases.
The CS5203A has a composite PNP−NPN output
transistor and requires an output capacitor for stability. A
detailed procedure for selecting this capacitor is included in
the Stability Considerations section.
Adjustable Operation
The adjustable regulator (CS5203A−1) has an output
voltage range of 1.25 V to 13 V. An external resistor divider
sets the output voltage as shown in Figure 10. The regulator
maintains a fixed 1.25 V (typical) 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 1.25 V across R1 and sets the
overall output voltage. The adjust pin current (typically
50 A) also flows through R2 and adds a small error that
should be taken into account if precise adjustment of V
OUT
is necessary.
The output voltage is set according to the formula:
V
OUT
V
REF
R1 R2
R1
I
Adj
R2
The term I
Adj
× R2 represents the error added by the adjust
pin current.
R1 is chosen so that the minimum load current is at least
10 mA. R1 and R2 should be the same type, e.g. metal film
for best tracking over temperature. The adjust pin is
bypassed to improve the transient response and ripple
rejection of the regulator.
C
Adj
I
Adj
Figure 10. Resistor Divider Scheme for the
Adjustable Version
V
REF
R
2
R
1
C
2
V
OUT
V
IN
C
1
V
IN
V
OUT
Adj
CS5203A−1
Stability Considerations
The output or compensation capacitor helps determine
three main characteristics of a linear regulator: satrtup delay,
load transient response and loop stability.
The capacitor value and type is based on cost, availability,
size and temperature constraints. A tantalum or aluminum
electrolytic capacitor is best, since a film or ceramic
capacitor with almost zero ESR, can cause instability. The
aluminum electrolytic capacitor is the least expensive
solution. However, when the circuit operates at low
temperatures, both the value and ESR of the capacitor will
vary considerably. The capacitor manufacturers data sheet
provides this information.
A 22 F tantalum capacitor will work for most
applications, but with high current regulators such as the
CS5203A the transient response and stability improve with
higher values of capacitor. The majority of applications for
this regulator involve large changes in load current so the
output capacitor must supply the instantaneous load current.
