Applications Information: continued
electrolytic capacitor is best, since a film or ceramic capaci-
Output Voltage Sensing
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.
Since the CS5203-1 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.
A 22µF tantalum capacitor will work for most applications,
but with high current regulators such as the CS5203-1 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:
For the adjustable regulator, the best load regulation
occurs when R1 is connected directly to the output pin of
the regulator as shown in Figure 4. If R1 is connected to the
load, RC is multiplied by the divider ratio and the effective
resistance between the regulator and the load becomes
R1 + R2
RC ´
(
)
R1
RC = conductor parasitic resistance
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 network
should be as close as possible to the load for the best results.
conductor parasitic
resistance
R
C
VIN
VOUT
VIN
CS5203-1
R
LOAD
R
1
Adj
Protection Diodes
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 VIN drops. In
the CS5203-1 linear regulator, the discharge path is
R
2
through a large junction and protection diodes are not usu-
ally needed. If the regulator is used with large values of
output capacitance and the input voltage is instantaneous-
ly shorted to ground, damage can occur. In this case, a
diode connected as shown in Figure 3 is recommended.
Figure 4. Grounding scheme for the adjustable output regulator to min-
imize parasitic resistance effects.
Calculating Power Dissipation and Heat Sink Requirements
The CS5203-1 linear regulator includes thermal shutdown
and current limit circuitry to protect the device. High
power regulators such as these usually operate at high
junction temperatures so it is important to calculate the
power dissipation and junction temperatures accurately to
ensure that an adequate heat sink is used.
IN4002
(optional)
VOUT
VIN
VOUT
VIN
C1
CS-5203-1
The case is connected to VOUT on the CS5203-1 , and elec-
trical isolation may be required for some applications.
Thermal compound should always be used with high cur-
rent regulators such as these.
R
C2
1
Adj
The thermal characteristics of an IC depend on the follow-
ing four factors:
R
2
CAdj
1. Maximum Ambient Temperature TA (¡C)
2. Power dissipation PD (Watts)
3. Maximum junction temperature TJ (¡C)
4. Thermal resistance junction to ambient RQJA (C/W)
These four are related by the equation
Figure 3. Protection diode scheme for large output capacitors.
6
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
