SG6905SZ Fairchild Semiconductor, SG6905SZ Datasheet - Page 5

• Manufacturer Part Number: SG6905SZ
• Description: IC PWM CTLR PFC/FLYBACK 20-SOP
• Manufacturer: Fairchild Semiconductor

Specifications of SG6905SZ

• Mode: Average Current
• Frequency - Switching: 65kHz
• Current - Startup: 10µA
• Voltage - Supply: 16 V ~ 20 V
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 20-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

© 2007 Fairchild Semiconductor Corporation
SG6905 • Rev. 1.1.2
Pin Definitions
Pin #
10
11
12
13
14
15
16
17
18
19
20
1
2
3
4
5
6
7
8
9
PFC_ON
ISENSE
FBPWM
Name
OPWM
FBPFC
VRMS
IPWM
AGND
OPFC
OTP
IPFC
GND
VDD
RDY
VEA
IMP
SS
IAC
IEA
RI
Description
Line Voltage Detection. The pin is used for PFC multiplier, brownout protection. For brownout
protection, the controller is disabled after a delay time when the VRMS voltage drops below a
threshold.
Reference Setting. One resistor connected between RI and ground determines the switching
frequency. The switching frequency is equal to [1560 / R
if R
Over-Temperature Protection. This pin supplies an over-temperature-protection signal. A
constant current is output from this pin. An external NTC thermistor must be connected from
this pin to ground. The impedance of the NTC thermistor decreases whenever the temperature
increases. Once the voltage of the OTP pin drops below the OTP threshold, the SG6905 is
disabled.
Output for PFC Current Amplifier. This is the output of the PFC current amplifier. The signal
from this pin is compared with an internal saw-tooth and hence determines the pulse width for
PFC gate drive.
Inverting Input for PFC Current Amplifier. The inverting input of the PFC current amplifier.
Proper external compensation circuits result in excellent input power factor via average-
current-mode control.
Non-Inverting Input for PFC Current Amplifier. The non-inverting input of the PFC current
amplifier and also the output of multiplier. Proper external compensation circuits result in
excellent input power factor via average-current-mode control.
Peak Current Limit Setting for PFC.
PWM Feedback Input. The control input for voltage-loop feedback of PWM stage. It is
internally pulled high through a 6.5kΩ resistance. Usually an external opto-coupler from
secondary feedback circuit is connected to this pin.
PWM Current Sense. The current-sense input for the flyback PWM. Via a current-sense
resistor, this pin provides the control input for peak-current-mode control and cycle-by-cycle
current limiting.
Ground. Signal ground.
PWM Soft-Start. During startup, the SS pin charges an external capacitor with a 50µA
(R
In the event of a protection condition occurring and/or PWM being disabled, the SS pin is
quickly discharged.
PWM Gate Drive. The totem-pole output drive for the flyback PWM MOSFET. This pin is
internally clamped under 17V to protect the MOSFET.
Ground. Power ground.
PFC Gate Drive. The totem-pole output drive for the PFC MOSFET. This pin is internally
clamped under 17V to protect the MOSFET.
Supply. The power-supply pin.
Ready-Signal Output. This pin outputs a ready signal to control the power-on sequence. Once
the SG6905 is turned on and the FBPFC (PFC feedback input) voltage is higher than 2.7V, the
pin locks to HIGH impedance. Disabling the SG6905 resets this pin to LOW.
Remote On/Off. The PFC stage disables whenever the voltage at this pin exceeds 2.45V.
Voltage Feedback Input for PFC. The feedback input for PFC voltage loop. The inverting
input of PFC error-amp. This pin is connected to the PFC output through a divider network.
Error-Amp Output for PFC Voltage Feedback Loop. The error-amp output for PFC voltage
feedback loop. A compensation network (usually a capacitor) is connected between this pin
and ground. A large capacitor value results in a narrow bandwidth and hence improves the
power factor.
Input AC Current. Before startup, this input is used to provide startup current for V
normal operation, this input is used to provide current reference for the multiplier.
I
=24kΩ) constant current source. The voltage on FBPWM is clamped by SS during startup.
I
is equal to 24kΩ, then the switching frequency is 65KHz.
5
I
]KHz, where R
I
is in kΩ. For example,
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. For