CS5207-3
Typical Performance Characteristics: continued
0.200
0.175
Output Voltage Deviation (%)
Ripple Rejection (dB)
100.0
90.0
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.150
0.125
T
CASE
= 125°C
0.100
0.075
T
CASE
= 25°C
0.050
0.025
0.000
0
1
2
3
4
5
6
7
Output Current (A)
T
CASE
= 0°C
T
CASE
= 25°C
I
OUT
= 7A
(V
IN
Ð V
OUT
) = 3V
V
RIPPLE
= 1.6V
PP
0.0
10
1
10
2
10
3
Frequency (Hz)
10
4
10
5
Load Regulation vs. Output Current
Ripple Rejection vs. Frequency
Applications Information
The CS5207-3 linear regulator provides a fixed 3.3V out-
put at currents up to 7A. The regulator is protected
against short circuit, and includes 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 CS5207-3 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.
work should be as close as possible to the load for the best
results.
Protection Diodes
Stability Considerations
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 is based on cost, availability,
size and temperature constraints. A tantalum or aluminum
electrolytic capacitor is best, since a film or ceramic capaci-
tor with almost zero ESR can cause instability. The alu-
minum 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 CS5207-3 the
transient response and stability improve with higher val-
ues of capacitor. The majority of applications for this regu-
lator involve large changes in load current so the output
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-
3
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 CS5207-3 regulator, the discharge path is through a
large junction and protection diodes are not usually need-
ed. If the regulator is used with large values of output
capacitance and the input voltage is instantaneously short-
ed to ground, damage can occur. In this case, a diode con-
nected as shown in Figure 1 is recommended.
IN4002
V
IN
C
1
V
IN
(optional)
V
OUT
V
OUT
C
2
CS5207-3
Gnd
Figure 1. Protection diode scheme for fixed output regulator.
Output Voltage Sensing
Since the CS5207-3 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.
Best load regulation occurs when the regulator is connect-
ed to the load as shown in Figure 2.
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
