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NCP4326
http://onsemi.com
4
PIN FUNCTION DESCRIPTION
Pin No.
Symbol
Type
Description
1
CP1
Error Amplifier
Output 1
This pin is the output of the error amplifier 1 (monitoring the secondary voltage #1) and is
available for loop compensation purpose.
2
FB1
Voltage
Feedback 1
This is the inverting input of the error amplifier 1. It is connected to the secondary voltage
#1 via a bridge resistor divider.
3
EN2
SoftStart and
Enable or Disable
the Driver 2
This pin enables or disables the driver 2. An internal current source with an external
capacitor generates also a softstart feature for limiting the startup peak current on the
controlled output.
This pin can be left open and by default it enables the driver 2, but without softstart
feature.
4
CP2
Error Amplifier
Output 2
This pin is the output of the error amplifier 2 (monitoring the secondary voltage #2) and is
available for loop compensation purpose.
5
FB2
Voltage
Feedback 2
This is the inverting input of the error amplifier. It is connected to the secondary voltage #2
via a bridge resistor divider.
6
Ct
Ct Pin
Connect the timing capacitor between Ct and the ground.
7
Sync
Synchronization
Pin
This pin monitors the main secondary winding, detects the beginning and the end of the
demagnetization phase (T
OFF
time on the primary winding) and allows the regulation on
the two secondary outputs.
8
CPm
Shunt Regulator
Output
This pin is the output of the shunt regulator (monitoring the main secondary voltage). An
open collector configuration is implemented.
9
FBm
Main Voltage
Feedback
This is the inverting input of the internal error amplifier. It is connected to the main output
voltage via a bridge resistor divider.
10
STBY
Standby
This pin is internally pulled up and allows standby mode feature. This pin can be left open
and by default it enables standard working mode. When this pin is pulled down standby
mode is activated and the quiescent current is reduced to the minimum. The output drivers
are disabled.
11
DRV2
Output Driver 2
This output directly drives the gate of a power MOSFET.
12
Vcc
Supplies the IC
This pin is connected to the main secondary output voltage and internally powers the IC.
13
DRV1
Output Driver 1
This output directly drives the gate of a power MOSFET.
14
Flux
Voltage image of
the magnetic flux
A RC network connected between this pin and a forward winding or a negative output
winding generates the transformer’s flux image. This flux image is compared to a slow
ramp generated on ENx pin for the softstart Duty Cycle generation controlling the both
outputs.
15
GND
The IC ground
16
EN1
SoftStart and
Enable or Disable
the driver 1
This pin enables or disables the driver 1. An internal current source with an external
capacitor generates also a softstart feature for limiting the startup peak current on the
controlled output.
This pin can be left open and by default it enables the driver 1, but without softstart
feature.