SP6231 Datasheet, PDF (4/10 Pages) Sipex Corporation – 500mA, 3.3V Linear Regulator with Auxiliary Backup

General Overview
The SP6231 combines a linear regulator with an
auxiliary backup. When the main supply volt-
age is applied at V_IN, the SP6231 acts as a
regulator. It supplies 3.3V at its output and
sources up to 500mA with an overall accuracy
of ±3%. Full protection with both current limit
and thermal shutdown is provided. When the
main supply drops below 4.4V, the output is
switched through an internal PFET to the auxil-
iary supply input.
A typical application is a USB peripheral (for
instance a digital camera) that in normal opera-
tion draws power from a battery supply (V_AUX)
but when it is plugged into the USB port will
recognize the main power supply availability
(V_IN) and draw its power from there, switching
over from the battery to the main power supply.
When the USB peripheral is removed from the
USB port, the output is switched back “glitch
free” to the battery supply so the peripheral sees
no supply interruption. Other applications in-
clude NIC cards, desktop computers, power
supplies with multiple input sources and
PCMCIA/PCI interface cards.
Modes of Operation
There are 2 modes of operation. The first mode
is the LDO mode when the main supply (V_IN) is
above 4.5V. At this point (independent of what
voltage the auxiliary supply is at) the SP6231
acts as an LDO with an output of 3.3V capable
of delivering up to 500mA. In this mode all
circuitry is powered off of the main supply V_IN.
The second mode, the backup switch mode,
occurs when V_IN drops below the auxiliary
supply (and below the 4.4V LDO mode). In this
mode the output is directly connected to the
auxiliary input through an internal 0.2Ω PFET
switch. All circuitry is powered off of the aux-
iliary supply. When the main supply is below
4.4V but still greater then the auxiliary supply,
the output is connected to the auxiliary supply
but most internal circuitry is still powered off of
the main supply. How this effects quiescent
currents can be seen in Figure 1.
THEORY OF OPERATION
120
100
IIN
IAUX
80
60
40
20
0
0
1
2
3
4
5
6
VIN (V)
Figure 1. Ground pin current vs. input voltage
(V_AUX = 3.3V, no load)
Linear Regulator Mode
When the main supply of the SP6231 (V_IN) is
above 4.5V, the part is in linear regulated LDO
mode (regardless of the auxiliary supply level).
It sources 3.3V (±3%) up to 500mA.
+3.3V Auxiliary Switch Mode
When the main supply falls below 4.4V, the
output is connected to the auxiliary supply
through an internal 0.2Ω PFET switch.
Sense Pin
In the LDO mode, a sense pin provides a Kelvin
connection with a 3.3V feedback (always tie
this pin to the point of regulation). If an accurate
3.3V supply is needed some distance away from
the SP6231, a drop in voltage might occur due to
the resistance of the length of the trace from the
SP6231 to where the supply is needed. For a
0.5Ω trace carrying 500mA the drop would be
0.25V leaving 3.05V at the supply destination.
By Kelvin connecting the sense pin to the supply
destination the SP6231 will adjust its output
voltage (to 3.55V) so that the voltage is 3.3V at
the supply destination. If this accuracy is of no
concern, the sense pin can simply be tied to the
output pin. The sense pin draws 15µA of current.
Thermal and Overcurrent Protection
Both the LDO switch and the backup switch
have overcurrent and thermal protection. The
overcurrent protection will limit the output cur-
rent to 1A for the LDO and 0.8A for the backup
switch typically. When the SP6231 heats up
above 165°C (due to power consumption in the
chip), both switches will be opened so the part
can cool down. Once the temperature drops by
15°C, the SP6231 will turn on again.
Date: 5/25/04
SP6231 500mA, 3.3V Linear Regulator
4
© Copyright 2004 Sipex Corporation