CS5201-3
Typical Performance Characteristics: continued
3.5
200
100
Voltage Deviation (mV)
3.3
3.1
2.9
0
2.7
I
SC
(A)
0
1
2
3
4
5
6
7
8
9
10
Time
mS
C
OUT
=C
IN
=22mF Tantalum
-100
-200
2.5
2.3
2.1
1.9
1.7
1.5
1.0
1.5
2.0
2.5
V
IN
- V
OUT
(V)
3.0
3.5
4.0
Load Step (mA)
1000
500
0
Transient Response
Short Circuit Current vs. V
IN
- V
OUT
Applications Information
The CS5201-3 linear regulator provides a fixed 3.3V out-
put voltage at currents up to 1A. The regulator is protect-
ed against overcurrent conditions and includes thermal
shutdown.
The CS5201-3 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.
Stability Considerations
Protection Diodes
The output or compensation capacitor helps determine
three main characteristics of a linear regulator: start-up
delay, load transient response and loop stability.
The capacitor value and type are based on cost, availabili-
ty, size and temperature constraints. A tantalum or alu-
minum 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 solu-
tion. However, when the circuit operates at low tempera-
tures, both the value and ESR of the capacitor will vary
considerably. The capacitor manufacturersÕ data sheet pro-
vides this information.
A 22µF tantalum capacitor will work for most applications,
but with high current regulators such as the CS5201-3 the
transient response and stability improve with higher val-
ues of capacitance. The majority of applications for this
regulator involve large changes in load current so the out-
put capacitor must supply the instantaneous load current.
The ESR of the output capacitor causes an immediate drop
in output voltage given by:
ÆV = ÆI
´
ESR
For microprocessor applications it is customary to use an
output capacitor network consisting of several tantalum
and ceramic capacitors in parallel. This reduces the overall
ESR and reduces the instantaneous output voltage drop
under load transient conditions. The output capacitor net-
work should be as close as possible to the load for the best
results.
4
When large external capacitors are used with a linear regu-
lator it is sometimes necessary to add protection diodes. If
the input voltage of the regulator gets shorted, the output
capacitor will discharge into the output of the regulator.
The discharge current depends on the value of the capaci-
tor, the output voltage and the rate at which V
IN
drops. In
the CS5201-3 linear regulator, the discharge path is
through a large junction and protection diodes are not
usually needed. If the regulator is used with large values
of output capacitance and the input voltage is instanta-
neously shorted to ground, damage can occur. In this case,
a diode connected as shown in Figure 1 is recommended.
IN4002
V
IN
C
1
V
IN
(optional)
V
OUT
V
OUT
CS5201-3
C
2
GND
Figure 1. Protection diode scheme for large output capacitors.
Output Voltage Sensing
Since the CS5201-3 is a three terminal regulator, it is not
possible to provide true remote load sensing. Load regula-
tion is limited by the resistance of the conductors connect-
ing the regulator to the load. For best results, the regulator
should be connected as shown in figure 2.
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
