cs5231-3 ON Semiconductor, cs5231-3 Datasheet - Page 6

• Manufacturer Part Number: cs5231-3
• Description: 500 Ma, 3.3 V Linear Regulator With Auxiliary Control
• Manufacturer: ON Semiconductor

contains an auxiliary drive control feature. When V
greater than the typical 4.5 V threshold, the IC functions as
a linear regulator. It provides up to 500 mA of current to a
load through a composite PNP−NPN pass transistor. An
output capacitor greater than 10 mF with equivalent series
resistance less than 1.0 W is required for compensation.
More information is provided in the Stability Considerations
section.
allows a load to remain powered even if the V
the IC is absent. An external p−channel FET is the only
additional component required to implement this function if
an auxiliary power supply is available. The PFET gate is
connected to the AuxDrv lead. The PFET drain is connected
to the auxiliary power supply, and the PFET source is
connected to the load. The polarity of this connection is very
important, since the PFET body diode will be connected
between the load and the auxiliary supply. If the PFET is
connected with its drain to the load and its source to the
supply, the body diode will be forward−biased if the
auxiliary supply is turned off. This will result in the linear
regulator providing current to everything on the auxiliary
supply rail.
resistor and to a saturating NPN transistor that acts as a
switch. If the V
connect the PFET gate to ground through the 10 kW resistor,
and the PFET will conduct current to the load.
rise until it reaches a typical voltage of about 650 mV. The
NPN transistor connected to the AuxDrv lead will saturate
at this point, and the gate of the PFET will be pulled down
to a typical voltage of about 100 mV. The PFET will
continue to conduct current to the load.
regulator output is disabled until V
threshold of 4.5 V. During this time, the load continues to be
powered by the auxiliary driver. Once the 4.5 V V
threshold is reached, the saturating NPN connected to the
AuxDrv lead turns off. The on−chip 10 kW pull−up resistor
will pull the PFET gate up to V
The linear regulator turns on at the same time. An external
compensation capacitor is required for the linear regulator
to be stable, and this capacitance also serves as a charge
reservoir to minimize any “glitching” that might result
during the supply changeover. Hysteresis is present in the
AuxDrv circuitry, requiring V
after the linear regulator is providing power to the load
before the AuxDrv circuitry can be re−enabled.
The CS5231−3 is a fixed 3.3 V linear regulator that
The CS5231−3 provides an auxiliary drive feature that
The AuxDrv lead is internally connected to a 10 kW
As the V
The V
IN
IN
supply voltage will continue to rise, but the linear
supply begins to rise, the AuxDrv lead will also
THEORY OF OPERATION
IN
supply is off, the AuxDrv output will
IN
IN
to drop by 100 mV (typical)
, thus turning the PFET off.
IN
reaches a typical
APPLICATION INFORMATION
IN
supply for
http://onsemi.com
IN
IN
is
6
V
V
V
AUXDRV
AUXDRV
“Oscillatory Performance” as the Linear Regulator
AUXDRV
Changes the V
V
V
V
V
OUT
OUT
Figure 15. Power−Down, V
V
IN
V
OUT
Figure 14. Power−Up, V
IN
IN
Figure 13. Initial Power−Up, V
Note DV = I R
I
OUT
I
I
Present R
OUT
OUT
= 375 mA V
OUT
= STARTUP 375 mA
Node. I
= 375 mA V
DS(ON)
OUT
AUX
OUT
AUX
AUX
= 8.8 W
= 3.30 V
AUX
9 130 mV
y R
= 3.3 V. Note the
= 3.30
= 3.3 V. Again,
DS(ON)
AUX
9 130 mV
Not