PS0100

OPERATION

The PS0100 is a compact, high-efficiency, synchronous

boost converter in a SOT-26 package designed for space-

restricted applications. The part is available with

adjustable output voltages ranging from 2.5V to 5.0V. It

is able to start up with input voltages as low as 0.8V and

operate with input voltages down to 0.5V.

With its

internal synchronous rectifier and low on-resistance of

the internal NMOS switch, the device maintains high

efficiency over a wide range of load current. As shown in

the Block Diagram, the PS0100 consists of accurate band

gap core, error amplifier, start-up oscillator and control

logic unit along with PMOS and NMOS switches. With

current mode PWM control, the PS0100 has ultra-fast line

and improved load regulation. Moreover, the PS0100

provides real shutdown circuitry which disconnects the

output from the input during shutdown and results in the

discharge of the output to ground.

conductive path through the body of the PMOS, the

output is allowed to go to zero during shutdown, drawing

zero current from the input.

Output Voltage Selection

The PS0100 features a user-adjustable output through an

external feedback network. A voltage divider from VOUT

to ground programs the output voltage via FB from 2.5V

to 5V using the following equation:

= V

July 2007

www.picsemi.com

© 2007 Power IC. All Rights Reserved.

10

Start-Up Mode

The PS0100 starts up typically at 0.8V. When it is turned

on, the device gets its start up bias from VIN. A start-up

oscillator, which runs typically at 650 KHz, takes the

over.

Internal PMOS and NMOS Switches

The PS0100 features a 0.45

Ω NMOS switch and a 0.6Ω

PMOS switch. In normal operation, these switches are

alternatively turned on and thus initiate the charging of

the inductor from VIN and then discharging of it to the

output capacitor and the load. However, between the

event of one switch turning off and the other turning on,

a dead time is provided to avoid a huge in-rush current

from the output to ground via switches. During the dead

time, both switches remain off and the inductor

discharges via the body diode of the PMOS switch to the

output.

True Shutdown Mode

The PS0100 is designed to allow for true shutdown by

managing the body diode of the PMOS switch. As the

PMOS switch is turned off and there is no

Thermal Overload Protection

Thermal overload protection limits the total power

dissipation in the PS0100. When the junction temperature

shutdown logic and turns off most of the internal

circuitry. The thermal sensor turns the internal circuitry

on again after the IC’s junction temperature drops by

15

°C.

Thermal overload protection is designed to protect the

PS0100 in the event of a fault condition. For continuous

operation, do not exceed the absolute maximum junction

Current Limit and Short Circuit Protection

The PS0100 includes a current limiter that monitors the

peak inductor current through the NMOS switch and

turns the NMOS switch off when the inductor peak

current exceeds 850mA. Because of its true shutdown

feature, the IC is allowed to be short-circuited. The

thermal shutdown turns off the regulator in the event of

excessive heating when the die temperature reaches

145

°C.

Light Load Operation

The PS0100 provides improved light load efficiency. The

internal zero current comparator monitors the inductor

current to the load and shuts off the PMOS switch once

this current reduces to some low value (typically 50mA).

This prevents the inductor current from reversing its

polarity, avoiding back-charging and thus improving the

efficiency at light loads. At that time, both the NMOS and

PMOS switches remain off. However, normal operation

starts again when the output voltage falls below the

regulation point. The IC automatically skips pulses at light

load, thus providing better efficiency.