Fairchild SG6846B service manual

SG6846B Highly Integrated Green-Mode PWM Controller

SG6846B — Highly Integrated Green-Mode PWM Controller

October 2008

Features

 Low Startup Current: 8µA  Low Operating Current: 3.7mA  Peak-Current Mode Operation with Cycle-by-cycle

Current Limiting

 PWM Frequency Continuously Decreasing with

Burst Mode at Light Loads

 V

Over Voltage Protection (OVP)

 AC Input Brownout Protection with Hysteresis  Constant Output Power Limit (Full AC Input Range)  Internal Latch Circuit for OVP, OTP, and OCP

(BLSY, BLSZ)

 Two-level OCP Delay with 200ms  Programmable PWM Frequency with Frequency

Hopping

 OCP Threshold is 2/3 Peak Current Limit  Soft Startup Time: 5ms

Applications

General-purpose switch-mode power supplies and flyback power converters, including:

 Power Adapters  Open-frame SMPS  SMPS with Surge-current Output, such as for

Printers, Scanners, Motor Drivers

Description

The highly integrated PWM controller, SG6846B, provides several features to enhance the performance of fly-back converters. To minimize standby power consumption, a proprietary green-mode function provides off-time modulation to continuously decrease the switching frequency under light-load conditions. Under zero-load conditions, the power supply enters burst-mode. This completely shuts off PWM output. If V

is larger than around 1.6V, PWM pulses out. This

green-mode function enables power supplies to meet international power conservation requirements.

The SG6846B is designed for SMPS with surge-current output. It is incorporated with a two-level OCP function. Besides, the cycle-by-cycle current limiting, if the switching current is higher than OCP threshold and lasts for 200ms, SG6846B stops gate immediately and latches itself (BLSY version) or restarts after V charges up to 16.5V (BCSY version). SG6846B also integrates frequency-hopping function internally. The frequency hopping function helps reduce EMI emission of a power supply with minimum line filters. It has builtin synchronized slope compensation, proprietary internal compensation for constant output power limit over universal AC input range. The gate output is clamped at 18V to protect the external MOSFET from over-voltage damage.

Protection include: AC input brownout protection with hysteresis and V temperature protection, an external NTC thermistor can be applied to sense the ambient temperature. When OCP, V circuit is used to latch-off the controller. The latch resets when V

SG6846B is available in 8-pin SOP package.

OVP, or OTP are activated, an internal latch

supply is removed.

over-voltage protection. For over-

Ordering Information

Part

Number

SG6846BLSY -40 to +105°C Yes Green 8-Pin Small Outline Package (SOP) Tape & Reel

SG6846BLSZ -40 to +105°C Yes RoHS 8-Pin Small Outline Package (SOP) Tape & Reel

SG6846BCSY -40 to +105°C No Green 8-Pin Small Outline Package (SOP) Tape & Reel

SG6846BCSZ -40 to +105°C No RoHS 8-Pin Small Outline Package (SOP) Tape & Reel

For Fairchild’s definition of “green” Eco Status, please vis i t : http://www.fairchildsemi.com/company/green/rohs_green.html.

Operating

Temperature Range

OCP

Latch

Eco

Status

Package

Packing

Method

Typical Application

AC input

EMI

Filter

VINRIVDD GATE

SG6846B — Highly Integrated Green-Mode PWM Controller

VO+

VO-

Block Diagram

0.9V/0.7V

VIN

VDD

-TH-G

UVLO

16.5V/10.5V

SENSE

GND

SG6846B

Figure 1. Typical Application

Over Power Compersation

0.895-0.065

Internal BIAS

Latch

XVIN

VDD

Soft Driver

Slope

Green Mode

Blanking Circuit

OSC

Compensation

6.2V

GATE

SENSE

1.15V

23.6V

1.05V

Debounce

OTP Delay

SCP Delay

OCP Delay

GND

Figure 2. Block Diagram

Marking Information

SG6846BFTP

XXXXXXXXYWWV

※ Marking for SG6846BLSZ (Pb-free)

SG6846BCSZ (Pb-free)

SG6846B — Highly Integrated Green-Mode PWM Controller

F: L = OCP Latch, C = OCP auto-recovery

T: S = SOP

P: Z = Lead Free + ROHS Compatible

Null = regular package

XXXXXXXX: Wafer Lot

Y: Year; WW: Week

V: Assembly Location

Figure 3. Top Mark 1

: Fairchild logo

Z: Plant Code

X: Year Code

Y: Week Code

TT: Die Run Code

F: L = OCP Latch, C = OCP auto-recovery

T: Package type, S = SOP

Green Package

P: Y =

M: Manufacturing flow code

※ Marking for SG6846BLSY (Green-compound) SG6846BCSY (Green-compound)

Figure 4. Top Mark 2

Pin Configuration

Figure 5. Pin Configuration

Pin Definitions

Pin # Name Function Description

1 GND Ground Ground.

The signal from the external compensation circuit is fed into this pin. The PWM

2 FB Feedback

3 VIN

4 RI

5 RT

6 SENSE Current Sense

7 VDD Power Supply

8 GATE Driver Output

Line-voltage

Detection

Reference

Setting

Temperature

Detection

duty cycle is determined in response to the signal from this pin and the currentsense signal from pin 6.

Line-voltage detection is used for brownout protection with hysteresis. Constant output power limit over universal AC input range is achieved using this pin. Add a low-pass filter to filter out line ripple on the bulk capacitor.

A resistor from the RI pin to ground generates a reference current source that determines the switching frequency. Increasing the resistance reduces the switching frequency. A 26k resistor results in a 65kHz switching frequency.

For over-temperature protection, an external NTC thermistor is connected from this pin to the GND pin. The impedance of the NTC decreases at high temperatures. Once the voltage of the RT pin drops below a threshold, PWM output is disabled.

The sensed voltage is used for peak-current-mode control and cycle-by-cycle current limiting. If the switching current is higher than OCP threshold and lasts for 200ms, SG6846B turns off immediately. This two-level OCP feature is especially suitable for SMPS with surge current output.

If an open-circuit failure occurs in the feedback loop, the internal protection circuit disables PWM output as long as V

The totem-pole output driver for the power MOSFET; internally clamped below 18V.

exceeds a threshold.

SG6846B — Highly Integrated Green-Mode PWM Controller

Absolute Maximum Ratings

Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only. All voltage values, except differential voltages, are given with respect to GND pin.

Symbol Parameter Min. Max. Unit

VDD Supply Voltage 30 V

VL Input Voltage to FB, SENSE, VIN, RT, RI Pins -0.3 7.0 V

PD Power Dissipation at TA<50°C SOP 400 mW

JC Thermal Resistance (Junction-to-Case) SOP 54.4 °C/W

TJ Operating Junction Temperature -40 +150 °C

Storage Temperature Range -65 +150 °C

STG

TL Lead Temperature, Wave Soldering, 10 Seconds +260 °C

ESD

Human Body Model, JESD22-A114 5.0

Charge Device Model, JESD22-C101 1.5

Recommended Operating Conditions

The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not recommend exceeding them or designing to Absolute Maximum Ratings.

Symbol Parameter Min. Max. Unit

TA Operating Ambient Temperature -40 +105 °C

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Fairchild SG6846B service manual

Specifications and Main Features

Frequently Asked Questions

User Manual