CS5231-3GDF8 ONSEMI [ON Semiconductor], CS5231-3GDF8 Datasheet - Page 10

• Manufacturer Part Number: CS5231-3GDF8
• Description: 500 mA, 3.3 V Linear Regulator with Auxiliary Control
• Manufacturer: ONSEMI [ON Semiconductor]

the maximum q
temperature rise is found to be
junction temperature of 125 C, and no heatsinking is
required. Since the D
part to the PC board by soldering both tab and leads will
provide superior performance with no PC board area
penalty.
package at a load of 500 mA. Using the dissipation from the
D
package of 110 C/W gives a temperature rise of 112 C.
Adding this to an ambient temperature of 70 C gives 182 C
junction temperature. This is an excessive temperature rise
but it can be reduced by adding additional cooling in the
form of added surface area of copper on the PCB. Using the
relationship of maximum temperature rise of
25 C/W. Subtracting these two numbers gives the allowable
thermal resistance from case to ambient:
q CA + q JA * q JC + 79.6°C W * 25°C W + 54.6°C W
54.6 C/W. We now look at Figure 20 and find the PCB trace
area that will be less than 54.5 C/W. Examination shows that
750 mm
would be the SOIC−8 part with the center 4 ground leads
soldered to pads in the center of a copper area about 27 mm
could result in a smaller required surface area.
as shown in the following pages. The schematic, bill of
materials and printed circuit board artwork can be used to
build the circuit. The design is very simple and consists of
two capacitors, a p−channel FET and the CS5231−3. Five
turret pins are provided for connection of supplies, meters,
oscilloscope probes and loads. The CS5231−3 power supply
management solution is implemented in an area less than 1.5
square inches. Due to the simplicity of the design, output
current must be derated if the CS5231−3 is operated at V
voltages greater than 7.0 V. Figure 21 provides the derating
curve on a maximum power dissipation if heatsink is added.
Operating at higher power dissipation without CS5231−3
heatsink may result in a thermal shutdown condition.
q JA (worst case) + DT JA P D + 80°C 1.018 W + 79.6°C W
2
First, we determine the need for heatsinking. If we assume
This is less than the maximum specified operating
We first determine the need for a heat sink for the SOIC−8
We calculate the thermal resistance allowed from junction
to air:
The thermal resistance from the die to the leads (case) is
The thermal resistance of this copper area will be
27 mm. A lower dissipation or the addition of air−flow
The CS5231−3 application circuit has been implemented
PAK example of 1018 mW and the q
DT JA + T J(MAX) * T A + 150°C * 70°C + 80°C
DT + P D
2
TYPICAL FUSED SOIC−8 DESIGN
of copper will provide cooling for this part. This
JA
q JA + 1.018 W
= 50 C/W for the D
DESCRIPTION
2
PAK has a large tab, mounting this
50°C W + 50.9°C
2
PAK, the maximum
JA
of the SOIC−8
http://onsemi.com
CS5231−3
IN
10
The V
The maximum input voltage to the IC is 14 V before damage
to the IC is possible. However, the specification range for the
IC is 4.75 V < V
The GND Connection
pins. The extra turret pin provides for connection of multiple
instrument grounds to the demonstration board.
The AuxDrv Connection
of the external PFET. This connection is also brought to a
turret pin to allow easy connection of an oscilloscope probe
for viewing the AuxDrv waveforms.
The V
an external 3.3 V supply and the PFET drain.
The V
CS5231−3 and the PFET source. This point provides a
convenient point at which some type of lead may be applied.
The V
The GND connection ties the IC power return to two turret
The AuxDrv lead of the CS5231−3 is connected to the gate
The V
The V
V
600
500
400
300
200
100
IN
0
GND
IN
AUX
OUT
TP1
TP2
TP3
5
+3.3 V
Figure 21. Demo Board Output Current
AUX
Connection
Figure 22. Application Circuit Schematic
IN
OUT
Connection
Connection
C1
connection is denoted as such on the PC board.
6
turret pin provides a connection point between
connection is tied to the V
TP4
V
IN
AUX
7
< 6.0 V.
GND
V
Derating vs. V
IN
8
CS5231−3
V
IN
9
AuxDrv
(Volts)
V
OUT
10
Q1
IN
U1
C2
11
OUT
12
lead of the
AuxDrv
13
TP5
TP6
14