Fairchild SG6846A service manual

SG6846A Highly Integrated Green-Mode PWM Controller

SG6846A — Highly Integrated Green-Mode PWM Controller

March 2012

Features

 Low Startup Current: 8µA  Low Operating Current: 3.7mA  Peak-Current Mode of 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  Two-level OCP Delay: 1600ms  Output Short-Circuited Delay Time: 100ms  Programmable PWM Frequency with

Frequency Hopping

 OCP Threshold is Half Peak Current Limit  Feedback Open-loop Protection with 1700ms Delay  Built-in Soft-Start

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 SG6846A is especially designed for SMPS with surge-current output, incorporated with a two-level OCP function. Besides the cycle-by-cycle current limiting, if the switching current is higher than two thirds the peakcurrent threshold for 1700ms, over-current protection is activated such that the SG6846A is latched off.

If the switching current is higher than two thirds of the peak-current threshold for 100ms, and the voltage on the V

is still higher than V

are latched off immediately once the V lower than V short circuit occurs.

SG6846A also integrates a frequency-hopping function internally to reduce EMI emission of a power supply with minimum line filters. Its built-in synchronized slope compensation provides proprietary internal compensation for constant output power limit over universal AC input range. Also, the gate output is clamped at 18V to protect the external MOSFET from over-voltage damage. Internal soft-start is built-in to soften the stress on the MOSFET and startup current during power on period.

Other protection functions include AC input brownout protection with hysteresis, V and over-temperature protection. For over-temperature protection, an external NTC thermistor can be applied to sense the ambient temperature. When OCP, V or OTP is activated, an internal latch circuit latches off the controller. The PWM pulses stay latched off until the power supply is disconnected from the mains outlet.

SG6846A controller is available in 8-pin SOP package.

+ 1V. This is useful when an output

DD-OFF

+ 1V, the PWM pulses

DD-OFF

over-voltage protection,

voltage is

OVP,

Ordering Information

Part Number

SG6846ALSY -40 to +105°C Yes 8-Pin Small Outline Package (SOP) Tape & Reel

SG6846ALSZ -40 to +105°C Yes 8-Pin Small Outline Package (SOP) Tape & Reel

SG6846ACSY -40 to +105°C No 8-Pin Small Outline Package (SOP) Tape & Reel

Operating

Temperature Range

OCP

Latch

Package

Packing

Method

Typical Application

AC input

EMI

Filter

VINRIVDD GATE

SG6846A — Highly Integrated Green-Mode PWM Controller

VO+

VO-

Block Diagram

GND

SENSE

SG6846A

Figure 1. Typical Application

Figure 2. Block Diagram

Marking Information

SG6846AFTP

XXXXXXXXYWWV

※ Marking for SG6846ALSZ (Pb-Free)

SG6846A — Highly Integrated Green-Mode PWM Controller

F: L = OCP Latch

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 =

※ Marking for SG6846ALSY (Green-compound), SG6846ACSY (Green-compound)

Figure 4. Top Mark 2

M: Manufacturing flow code

Pin Configuration

SG6846A — Highly Integrated Green-Mode PWM Controller

GND

VIN

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 1700ms, SG6846A 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 VDD exceeds a threshold.

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

GATE

VDD

SENSE

SG6846A — 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 25 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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