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 Soft−Start 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 soft−start 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 soft−start
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 soft−start Duty Cycle generation controlling the both
outputs.
15 GND The IC ground −
16 EN1 Soft−Start 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 soft−start 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 soft−start
feature.
