CS5231-3GDF8 ONSEMI [ON Semiconductor], CS5231-3GDF8 Datasheet - Page 9

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

need for an external reset signal. The monitoring circuitry is
located near the composite PNP−NPN output transistor,
since this transistor is responsible for most of the on−chip
power dissipation. The combination of current limit and
thermal shutdown will protect the IC from nearly any fault
condition.
circuitry will maintain voltage on the V
is absent. IC reliability and system efficiency are improved
by limiting the amount of reverse current that flows from
V
V
sets up the output voltage This resistor can range in value
from 6.0 kW to about 10 kW, and roughly 500 mA will flow
in the typical case. Current flow from V
limited to leakage current after the IC shuts down. On−chip
RC time constants are such that the output transistor should
be turned off well before V
in high on−chip power dissipation. This results in high
junction temperatures. Since the IC has a thermal shutdown
feature, ensuring the regulator will operate correctly under
normal conditions is an important design consideration.
Some heatsinking will usually be required.
parameters: ambient temperature (T
dissipation (P
the ambient air (q
(T
from the formula below:
determined by the design, while q
package manufacturer. The maximum junction temperature
for operation of the CS5231−3 within specification is
150°C. The maximum power dissipation of a linear
regulator is given as
where I
a heatsink to the design. A heatsink serves in some manner
to raise the effective area of the package, thus improving the
flow of heat from the package into the surrounding air. Each
material in the path of heat flow has its own characteristic
thermal resistance, all measured in °C per watt. The thermal
resistances are summed to determine the total thermal
resistance between the die junction and air. There are three
components of interest: junction−to−case thermal resistance
OUT
OUT
During normal system operation, the auxiliary drive
Most linear regulators operate under conditions that result
Thermal characteristics of an IC depend on four
Maximum ambient temperature and power dissipation are
It is possible to change the effective value of q
J
in °C). The maximum junction temperature is calculated
CALCULATING POWER DISSIPATION AND
to ground and from V
to ground through the feedback resistor divider that
T J(MAX) + T A(MAX) ) (q JA
P D(MAX) + (V IN(MAX) * V OUT(MIN) )
GND(MAX)
REVERSE CURRENT PROTECTION
HEATSINK REQUIREMENTS
D
in watts), thermal resistance from the die to
JA
is the IC bias current.
in °C per watt) and junction temperature
(I LOAD(MAX) ) V IN(MAX) )
I GND(MAX)
IN
OUT
drops below the V
to V
JA
IN
. Current flows from
is dependent on the
A
P D(MAX) )
OUT
OUT
in °C), power
to V
pin when V
OUT
JA
IN
by adding
voltage.
will be
http://onsemi.com
IN
9
(q
heatsink−to−air thermal resistance (q
equation for junction−to−air thermal resistance is
provided in the Packaging Information section of this data
sheet. The value of q
conducted out of the D
tab, and out of the SOIC−8 package by its IC leads that are
soldered directly to the PC board.
management. For surface mount components, this means
modifying the amount of trace metal that connects to the IC.
how much copper area is used, whether or not the IC is in
direct contact with the metal, whether or not the metal
surface is coated with some type of sealant, and whether or
not there is airflow across the PC board. The chart provided
below shows heatsinking capability of a square, single sided
copper PC board trace. The area is given in square
millimeters, and it is assumed there is no airflow across the
PC board.
the D
made assuming V
I
TYPICAL D
OUT(MAX)
JC
The value of q
Modification of q
The thermal capacity of PC board traces is dependent on
A typical design of the PC board surface area needed for
Maximum temperature rise
70
60
50
40
30
20
10
q JA (worst case) + DT P D + 80°C 1.018 W + 78.56°C W
0
), case−to−heatsink thermal resistance (q
DT + T J(MAX) * T A + 150°C * 70°C + 80°C
2
0
Figure 20. Thermal Resistance Capability of
PAK package is shown on page 11. Calculations were
P D + (5.25 V * 3.266 V)
= 500 mA, I
Copper PC Board Metal Traces
2
) (5.25 V)(0.005 A) + 1018 mW
PAK PC BOARD HEATSINK DESIGN
q JA + q JC ) q CS ) q SA
PC Board Trace Area (mm
IN(MAX)
JC
CS
2000
SA
both packages of the CS5231−3 are
2
PAK package by the IC leads and the
GND(MAX)
can be considered zero, since heat is
is the primary means of thermal
= 5.25 V, V
= 5.0 mA and T
4000
0.5 A
OUT(MIN)
SA
2
)
). The resulting
= 3.266 V,
A
CS
= 70°C.
) and
6000