Harman Kardon DVD 48, Service Manual

Page: 63 / 174

Product Specification
Highly-Integrated Green-Mode PWM Controller
SG6842
© System General Corp. www.sg.com.tw
Version 1.4(IRO33.0009.B5) Jan. 20, 2005
MARKING DIAGRAMS PIN CONFIGURATION
O
PIN DESCRIPTIONS
Pin No. Symbol Function Description
1 GND Ground Ground.
2 FB Feedback
The signal from the external compensation circuit is fed into this pin. The PWM duty cycle is
determined in response to the signal from this pin and the current-sense signal from Pin 6.
3 VIN Start-Up Input
For start-up, this pin is pulled high to the rectified line input. This pin is pulled via a resistor.
Since the start-up current requirement of the SG6842 is very small, a large start-up resistance
can be used to minimize power loss. Under normal operation, this pin is also used to detect the
line voltage. The line voltage is detected to compensate the output power limit, so that it can be
kept constant over a universal AC input range
4 RI
Reference
Setting
A resistor connected from the RI pin to ground will provide the SG6842 with a constant current
source. This current charges an internal capacitor. This determines the switching frequency.
Increasing the resistance will decrease the amplitude of the current from the current source,
and thereby reduce the switching frequency. Using a 26k
Ω resistor R
I
results in a 50uA
constant current I
I
and a 65kHz switching frequency.
5 RT
Temperature
Detection
For over-temperature protection. An external NTC thermistor is connected from this pin to
ground. The impedance of the NTC will decrease at high temperatures. Once the voltage of the
RT pin drops below a fixed limit of 1.05V, PWM output will be disabled.
SG6842 BFVTP
MXXXXXXYYWWV
8
1
B: B = Linearly Decreasing
Fre Burst-Mode
F: L = OTP Latch: The pin is
reset when AC is
disconnected.
C = Hysteresis OTP : The
pin is reset when the
temperature cools down.
V: V = OVP Latch
T : D = DIP, S = SOP
P : Z =Lead Free + ROHS
Compatible
Null=regular package
M : Mask Version
XXXXXX : Wafer Lot
YY : Year; WW : Week
V: Assembly Location
RI
VIN
GATE
VDD
SENSE
RT
GND
FB
3
1
2
5
6
8
7
4
6 SENSE Current Sense
Current sense. The sensed voltage is used for current-mode control and pulse-by-pulse
current limiting.
7 VDD Power Supply
Power Supply. If an open circuit failure occurs in the feedback loop, the internal protection
circuit will disable PWM output as long as VDD remains higher than 26V.
8 GATE Driver Output
The totem-pole output driver for the power MOSFET. A soft driving waveform is implemented
for improved EMI.
63
DVD48
harman/kardon