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Date: 5/25/04

SP6231 500mA, 3.3V Linear Regulator

© Copyright 2004 Sipex Corporation

General Overview

The SP6231 combines a linear regulator with an

auxiliary backup. When the main supply volt-

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-

but when it is plugged into the USB port will

recognize the main power supply availability

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

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

The second mode, the backup switch mode,

supply (and below the 4.4V LDO mode). In this

mode the output is directly connected to the

auxiliary input through an internal 0.2

Ω 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.

Linear Regulator Mode

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 0.2

Ω 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

0.5

Ω 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 15

µA 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.

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3456

Figure 1. Ground pin current vs. input voltage

THEORY OF OPERATION