Product Specification

- 9 -

Power Supply

Protection against over-voltage, short-circuit and

fault conditions is mandatory in PC power supplies. These

protection circuits can be realized by using many discrete

components and comparators, which occupy a lot of PCB

space and also add to assembling costs. This single chip

controller IC provides complete protection circuits, shunt

regulators, and PWM control function and with less

number of components. STC6105 is an ideal controller

IC for PC switching mode power supplies.

The features and benefits of this device are listed

below:

Over-voltage and under-voltage protection for 3.3V,

5V and 12V without external divider

Over-power protection.

UV protection for –12V and/or –5V.

Power-down warning for power good signal.

Power good signal and power-fail lockup

Remote on/off control.

Delay time for PSON and PS-off signal.

Two shunt regulator for 3.3V and 5V-Standby

regulation.

Complete pulse width modulation (PWM) control

circuitry.

On-chip oscillator.

Programmable Soft-Start.

Maximum 93% duty cycle

Few external components

More reliable system

Little space on PCB

Easy trouble-shooting and implementation

FEATURE DESCRIPTIONS

Over voltage protection can be implemented without

any additional components. Over-voltage sense

Levels or 3.3V, 5V, 12V are 4.1V, 6.1V, 14.5V

respectively.

Over current and/or short circuit protection can also

be achieved by using over-power protection, in

which OPP pin is connected to the current

transformer (driver transformer).

The power good signal is asserted to indicate the

3.3V, 5V and 12V is above the under voltage

threshold level. PG pin goes high when the above

condition is reached. A 2K pull up resistor may

connect to5V.

The VCC can be supplied from the 5V-standby.

When the VCC voltage is higher than 7V, besides the

shunt regulator, the circuit of STC6105 will be

shutdown and reset. No extra power supply is

needed.

Two internal high precision 431 shunt regulators are

built-in. It provides stable reference voltages.

Complete PWM control circuitry including the error

amplifier for push-pull or half-bridge operation.

Supervisory Circuit Operation

The PC generates the remote ON/OFF logic (PSON),

which is “Low” for power supply “On” and “High” to

switch off the power supply. The remote ON/OFF is

connected to PSON input.

APPLICATION GUIDES

Introduction

The application guide shows the key-feature of

STC6105

and illustrates how to use in an ATX

switching mode power supply (SMPS). STC6105

is

suitable

for

half-bridge,

push-pull

topology.

It

incorporates with a 4-channel supervisor, including

5V-standby. The PWM section of STC6105 comprises a

built-in 65kHz oscillator and high immunity circuits,

which protect the system from noise interference and

provide more noise margins for improper PCB layout.

STC6105 has OVP and UVP for 12V, 5V and 3.3V.

Besides, the NVP is used for negative voltage protection,

such as –12V and/or –5V. The UVAC (AC fails detection)

is applied to detect AC line condition. Two built-in

internal precision TL431 shunt regulators can be used for

3.3V or 5V auxiliary standby power.

AC Fails Detection

Through a resistor divider, UVAC is connected to

the secondary power transformer for detecting the AC line

condition. Once the voltage of UVAC is lower than 0.7V

for a period of time, such as 200usec, the PG (power good)

signal will be pulled low to indicate an AC line

power-down condition. The voltage amplitude of the

STC6105

Power Supply Supervisor + Regulator + PWM