FSD1000
3
Pin Definitions
Pin Number
Pin Name
Pin Function Description
1
V
FB,AUX
This pin is for the feedback control of the auxiliary power. This pin is internally
connected to the inverting input of the PWM comparator. The collector of an
opto-coupler is typically tied to this pin. For stable operation, a capacitor should
be placed between this pin and GND. Voltage mode control is employed for the
auxiliary power and the duty cycle ratio of Internal MOSFET for the auxiliary
power is proportional to the voltage of this pin. If the voltage of this pin exceeds
4.5V, the over load protection is triggered terminating the switching operation of
the main and auxiliary power (Auto-restart mode protection).
This pin is for the feedback control of the main power. This pin is internally
connected to the inverting input of the PWM comparator. The collector of an
opto-coupler is typically tied to this pin. For stable operation, a capacitor should
be placed between this pin and GND. Current mode control is employed for the
main power and the peak drain current of the external MOSFET for the main
power is proportional to the voltage of this pin. If the voltage of this pin exceeds
7V, the over load protection is triggered disabling the gating output for the main
power (Latch mode protection).
This pin is for the soft start of the main power. Soft start time is programmed by
a capacitor on this pin.
This pin is for the gate drive of the external MOSFET of the main power.
This pin is the positive supply voltage input. During startup, the power is supplied
by an internal high voltage current source that is connected to the Vstr pin. When
Vcc reaches 13.5V, the internal high voltage current source is disabled and the
power is supplied from auxiliary transformer winding.
This pin is for the current sense of the external MOSFET for the main power. It is
internally connected to the PWM comparator for the main.
This pin is for line under voltage detection. When the voltage of this in drops
below 1.4V the main power is shutdown. When the voltage drops below 0.8V,
the auxiliary power is shutdown.
This pin is for line over voltage detection and maximum duty cycle ratio change.
The maximum duty cycle ratio is set to be 50% when the voltage of LS2 pin is
higher than 2.4V. The maximum duty cycle ratio is increased to 67% when LS2
voltage goes below 2.0V. When the voltage of LS2 goes above 4.4V, the
switching operations for the main and auxiliary powers are disabled to protect
the switching devices.
This pin is for the current limit of the auxiliary power. The pulse-by-pulse current
limit level of the internal SenseFET is programmed by a resistor on this pin.
2
V
FB,MAIN
3
S/S
4
Output
5
Vcc
6
I
SENSE
7
LS1
8
LS2
9
I
LIM
10
NC
11
Drain
This pin is the high voltage power SenseFET drain. It is designed to drive the
auxiliary transformer directly.
This pin is connected directly to the high voltage DC link. At startup, the internal
high voltage current source supplies internal bias and charges the external
capacitor that is connected to the Vcc pin. Once Vcc reaches 13V, the internal
current source is disabled.
12
V
STR