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RS2051S: DescriptionNovel Low Cost Green-Mode PWM Controller with Soft Start & Mode; File Size519KB，13 Pages; ManufacturerOrister

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Novel Low Cost Green-Mode PWM Controller with Soft Start & Mode

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RS2051

Novel Low Cost Green-Mode PWM Controller

with Soft Start & Latch Mode

Description

The RS2051 is a highly integrated low cost current mode PWM controller, which is ideal for small power current mode of offline

AC-DC fly-back converter applications. Making use of external resistors, the IC changes the operating frequency and

automatically enters the PFM/CRM (Cycle Reset Mode) under light-load/zero-load conditions. This can minimize standby power

consumption and achieve power-saving functions. With a very low start-up current, the RS2051 could use a large value start-up

resistor (2Mohms). Built-in synchronized slope compensation enhances the stability of the system and avoids sub-harmonic

oscillation. Dynamic peak current limiting circuit minimizes output power change caused by delay time of the system over a

universal AC input range. Leading edge blanking circuit on current sense input could remove the signal glitch due to snubber

circuit diode reverse recovery and thus greatly reduces the external component count and system cost in the design. Cycle-by-

Cycle current limiting ensures safe operation even during short-circuit.

Excellent EMI performance is achieved built-in soft start with 1.2mS、soft driver and frequency jitter.

The RS2051 offers perfect protection like OVP(Over Voltage Protection)、OLP(Over Load Protection)、SCP(Short circuit

protection)、OTP、Sense Fault Protection

、LM

(Latch Mode) and OCP(Over current protection). The RS2051’s output driver

is soft clamped to maximum 16.5V to protect the power MOSFET. RS2051 is offered in SOT-23-6L, SOT-8 and DIP-8 packages.

Features

Low Cost, PWM&PFM&CRM (Cycle Reset Mode)

Low Start-up Current (about 1.5μA)

Low Operating Current (about 2.2mA)

Current Mode Operation

Under Voltage Lockout (UVLO)

Built-in Synchronized Slope Compensation

Built-in fixed soft start with 1.2mS

Built-in Frequency jitter for better EMI Signature

Programmable PWM Frequency

Audio Noise Free Operation

Leading edge Blanking on Sense input

Constant output power limiting for universal AC input

Range

SOT-23-6L、SOP8 and DIP-8 Pb-Free Packaging

Compatible with SG6848 (6849) / SG5701 / SG5848 /

LD7535 (7550) / OB2262 (2263) / OB2278（2279）

Soft Clamped GATE output voltage 16.5V

VDD over voltage protect 25.6V

Cycle-by-cycle current limiting

Sense Fault Protect ion

OTP (Over Temperature Protection)

Output SCP (Short circuit Protection)

Output OLP (Over Load Protection)

Latch mode After OLP&SCP

High-Voltage CMOS Process with ESD

Applications

Switching AC/DC Adaptor

Battery Charger

Open Frame Switching Power Supply

Standby Power Supplies

Set-Top Box Power Supplies

384X Replacement

Pin Configurations

DS-RS2051-02

September, 2007

www.Orister.com

Page No. : 5/13

OPERATION DESCRIPTION

Current Mode

Compared to voltage mode control, current mode control has a current feedback loop. When the voltage of the Sense resistor

peak current of the primary winding reaches the internal setting value V

, the register resets and the power MOSFET cuts off.

So, to detect and modulate the peak current cycle-by-cycle could control the output of the power supply. The current feedback

has a good linear modulation rate and a fast input and output dynamic impact, and avoid the pole that the output filter

inductance brings and the two-class system descends to the one-class. So it widens the frequency range and optimizes

overload protection and short circuit protection.

Startup Current and Under Voltage Lockout

The startup current of RS2051 is set to be very low so that a large value startup resistor can be used to minimize the power loss.

For AC to DC adaptor with universal input range design, a 2 MΩ, 1/8 W startup resistor and a 10uF/25V VDD hold capacitor

could be used.

The turn-on and turn-off threshold of the RS2051 is designed to 12.8V/7.8V. During startup, the hold-up capacitor must be

charge to 12.8V through the startup resistor. The hysteresis is implemented to prevent the shutdown from the voltage dip during

startup.

Internal Bias and OSC Operation

A resistor connected between RI pin and GND pin sets the internal constant current source to charge or discharge the internal

fixed capacitor. The charge time and discharge time determines the internal clock speed and the switching frequency.

Increasing the resistance will reduce the value of the input current and reduce the switching frequency. The relationship

between RI and PWM switching frequency follows the below equation within the RI allowed range.

OSC

6000

(

kHz

)

(

)

For example, a 100kΩ resistor RI could

generate a 13uA constant current and a 60kHz PWM switching frequency.

The suggested operating frequency range of RS2051 is within 30KHz to 150KHz.

Green Power Operation

The power dissipation of switching mode power supply is very important in zero load or light load condition. The major

dissipation results from conduction loss、switching loss and consume of the control circuit. However, all of them relates to the

switching frequency. There are many difference topologies has been implemented in different chip. The basic operation theory

of all these approaches intends to reduce the switching frequency under light-load or no-load condition.

The RS2051`s green power function adapts PWM、PFM and CRM combining modulation. When RI resistor is 100kΩ, the

PWM frequency is 60kHz in medium or heavy load operation. Through modifying the pulse width, The RS2051 could control

output voltage. The current of FB pin increases when the load is in light condition and the internal mode controller enters

PFM&PWM when the feedback current is over 1.37mA. The operation frequency of oscillator is to descend gradually. When the

feedback current is over 1.43mA, the frequency of oscillator is invariable, namely 22kHz.

To decrease the standby consumption of the power supply, Chip-Rail introduces the Cycle Reset Mode technology (CRM). If the

feedback current is over 1.45mA, mode controller of the RS2051 would reset internal register all the time and cut off the GATE

pin. While the output voltage is lower than the set value, the register would be set, the GATE pin operate again. So the

frequency of the internal OSC is invariable, the register would reset some pulses so that the practical frequency is decreased at

the GATE pin.

RS2051 Green-Power Function

DS-RS2051-02

September, 2007

www.Orister.com

RS2051S Related Products

	RS2051S	RS2051N	RS2051P	RS2051
Description	Novel Low Cost Green-Mode PWM Controller with Soft Start & Mode	Novel Low Cost Green-Mode PWM Controller with Soft Start & Mode	Novel Low Cost Green-Mode PWM Controller with Soft Start & Mode	Novel Low Cost Green-Mode PWM Controller with Soft Start & Mode

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