CS5201-1 Datasheet, PDF (6/9 Pages) Cherry Semiconductor Corporation – 1A Adjustable Linear Regulator

CS5201−1
Protection Diodes
When large external capacitors are used with a linear
regulator 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 capacitor, the
output voltage and the rate at which V_IN drops. In the
CS5201−1 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 instantaneously shorted
to ground, damage can occur. In this case, a diode connected
as shown in Figure 13 is recommended.
IN4002 (Optional)
V_IN
V_IN
V_OUT
V_OUT
CS5201−1
C₁
Adj
C₂
R₁
Calculating Power Dissipation and Heatsink
Requirements
The CS5201−1 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 Heatsink is used.
The case is connected to V_OUT on the CS5201−1,
electrical isolation may be required for some applications.
Thermal compound should always be used with high current
regulators such as these.
The thermal characteristics of an IC depend on the
following four factors:
1. Maximum Ambient Temperature T_A (°C)
2. Power dissipation P_D (Watts)
3. Maximum junction temperature T_J (°C)
4. Thermal resistance junction to ambient R_qJA (°C/W)
These four are related by the Equation
R₂
C_Adj
Figure 13. Protection Diode for Large Output
Capacitors
Output Voltage Sensing
Since the CS5201−1 is a three terminal regulator, it is not
possible to provide true remote load sensing. Load
regulation is limited by the resistance of the conductors
connecting the regulator to the load.
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 14. 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.
ǒ Ǔ RC
R1 ) R2
R1
where R_C = conductor parasitic resistance.
V_IN
V_IN
V_OUT
Conductor Parasitic
R_C
Resistance
CS5201−1
R₁
Adj
R_LOAD
R₂
Figure 14. Grounding Scheme for Adjustable Output
Regulator to Minimize Parasitic Resistance Effects
TJ + TA ) PD R_qJA
(1)
The maximum ambient temperature and the power
dissipation are determined by the design while the
maximum junction temperature and the thermal resistance
depend on the manufacturer and the package type.
The maximum power dissipation for a regulator is:
PD(max) + {VIN(max) * VOUT(min)}IOUT(max) ) VIN(max)IQ
(2)
where:
V_IN(max) is the maximum input voltage,
V_OUT(min) is the minimum output voltage,
I_OUT(max) is the maximum output current, for the
application
I_Q is the maximum quiescent current at I_OUT(max).
A Heatsink effectively increases the surface area of the
package to improve the flow of heat away from the IC and
into the surrounding air.
Each material in the heat flow path between the IC and the
outside environment has a thermal resistance. Like series
electrical resistances, these resistances are summed to
determine R_qJA, the total thermal resistance between the
junction and the surrounding air.
1. Thermal Resistance of the junction−to−case, R_qJC
(°C/W)
2. Thermal Resistance of the case to Heatsink, R_qCS
(°C/W)
3. Thermal Resistance of the Heatsink to the ambient
air, R_qSA (°C/W)
These are connected by the Equation:
R_qJA + R_qJC ) R_qCS ) R_qSA
(3)
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