SE3252 datasheet, PDF - EEWORLD Datasheet

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SE3252: Description21V 15μA AC/DC converter; CategoryPower management; File Size262KB，5 Pages; ManufacturerSINO-IC Microelectronic Co., Ltd.; Websitehttp://www.sino-ic.net; Shanghai Guangyu Ruixin Microelectronics Co., Ltd. specializes in the design, development and sales of semiconductor overvoltage protection devices and integrated circuits. It is one of the domestic suppliers that masters the core technology of semiconductor overvoltage protection devices and integrated circuits. They are used in communication systems, portable products, lithium battery protection, power system overvoltage protection, LED drive, etc.

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SE3252 Overview

21V 15μA AC/DC converter

Features

Product Name: 21V 15μA AC/DC Converter

Product model: SE3252

Product Description:

The SE3252 series switcher ICs cost effectively replace all power supplies up to 5W output power based on unregulated isolated linear transformer (50/60HZ). Unlike conventional PWM (pulse width modulation) controllers, they regulate the output voltage in a new method of off-time modulation control. The controller consists of a VCO (voltage control oscillator), Sense and logic circuit, VDD pin, under-voltage lockout circuit, protection for over-voltage, current limited circuit, leading edge blanking, over load protection and fault condition auto-restart. They are ideal low power AC/DC adapter/charger solution for portable devices.

product features:

Low start-up current: Typ.15 μA Max.25 μA

UVLO(under voltage lockout):Typ.12V start-up Typ.6V shut-down

Low operating current:Typ.2 mA Max.5 mA

LEB(leading edge blanking): Typ.300ns

OVP(over voltage protection): Typ.28 V

Operation Frequency: Typ.54KHZ(VDD=21V)

Output Driver Ability: Typ.15 mA

OLP(over load protection)

Universal AC input range

Constant voltage and constant current

Small SOT-23-6 Package

Applications:

AC/DC adapter/charger for cell/cordless phones, digital cameras, MP3/portable audio devices etc

LED Lighting

Replacements for linear transformers and RCC SMTPS

Package: SOT23-6

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SHANGHAI

MICROELECTRONICS CO., LTD.

July 2008

SE3252

Off Line AC/DC Switcher IC

Description

he SE3252 series switcher ICs cost effectively replace all power supplies up to 5W output power based on

unregulated isolated linear transformer (50/60HZ). Unlike conventional PWM (pulse width modulation)

controllers, they regulate the output voltage in a new method of off-time modulation control. The controller

consists of a VCO (voltage control oscillator), Sense and logic circuit, VDD pin, under-voltage lockout circuit,

protection for over-voltage, current limited circuit, leading edge blanking, over load protection and fault condition

auto-restart. They are ideal low power AC/DC adapter/charger solution for portable devices,

Features

• Low start-up current: Typ.15

μA

Max.25

μA

• UVLO(under voltage lockout):Typ.12V start-up Typ.6V shut-down

• Low operating current:Typ.2 mA Max.5 mA

• LEB(leading edge blanking): Typ.300ns

• OVP(over voltage protection): Typ.28 V

• Operation Frequency: Typ.54KHZ(VDD=21V)

• Output Driver Ability: Typ.15 mA

• OLP(over load protection)

• Universal AC input range

• Constant voltage and constant current

• Small SOT-23-6 Package

Applications

•AC/DC

adapter/charger for cell/cordless phones, digital cameras, MP3/portable audio devices etc

• LED Lighting

• Replacements for linear transformers and RCC SMTPS

Package

SHANGHAI

MICROELECTRONICS CO., LTD.

July 2008

Function Description

1. Under Voltage Lockout

The turn-on and turn-off thresholds of the SE3252 are fixed internally at 12V/6V. During start-up, the hold-up

capacitor must be charger to 12V through the start-up resistor, so that the SE3252 can be enabled. The hold-up

capacitor will continue to supply VDD until power can be delivered from the auxiliary winding of the main

ransformer, When VDD drop below 6V, IC will be shut-down, and have to start-up again. This UVLO hysteretic

window ensures that SE3252 can start-up very well.

2. Leading Edge Blanking

When the power BJT is switched on, a voltage spike will inevitably occur at the sense pin. To avoid premature

termination of the switching pulse, a 300 ns leading-edge blanking time is built in SE3252. Conventional RC

filtering can be omitted. During this blanking period, the current-limit comparator is disabled and it cannot switch

off the gate driver.

3. Voltage Control Oscillator

The sense circuit of SE3252 series will sense the voltage of VDD pin (also the power pin of SE3252) and then

control the frequency of the oscillator. The max frequency of SE3252 series is set to the rated output power

point,for example SE3252 is set to 54 KHZ Two signals are generated from the oscillator: the maximum duty

cycle signal (DC max) and the clock signal that indicates the beginning of each switching cycle.

4. Sense Circuit

A resistor voltage divided circuit is connected between the VDD pin and GND pin in order to sample the

feed-back voltage at VDD pin. When the voltage of VDD pin exceeds 21V, IC will come into constant voltage

control mode,shut- down the output pin and start a bypass circuit. This bypass circuit is linearly controlled by the

feedback voltage. When the voltage of VDD pin falls below 21V, the off-time linearly increases in order to have a

constant current output.

5. Gate Output

Unlike other chips, SE3252 used a constant current circuit to drive the output BJT. The output current is fixed at

15mA, select the appropriate HFE of BJT could have a different output power.

6. Fault Condition Auto-restart

In the event of a fault condition such as output over-load or short circuit, SE3252 series enter into auto-restart

operation. It is using the turn-on and turn-off threshold again. SE3252 series are working in start mode to protect

the system from damage caused by the fault condition.

7. Current Limit

The current through the power BJT is detected by the current limit circuit. Then the current flows through the

sense-resistor and makes the voltage on Sense pin ramp up. And when this voltage exceeds the internal threshold

(Vlimit), the power BJT is turned off immediately.

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