CS |
4 |
I |
The current-sense (CS) input connects to a ground-referenced current-sense resistor in series with the power switch. The resulting voltage monitors and controls the peak primary current. A series resistor is added to this pin to compensate for peak switch current levels as the AC-mains input varies. |
DRV |
3 |
O |
DRV is an output pin used to drive the gate of an external high voltage MOSFET switching transistor. |
FB |
1 |
I |
The feedback (FB) input receives a current signal from the optocoupler output transistor. An internal current mirror divides the feedback current applies it to an internal pullup resistor to generate a control voltage, VCL. The voltage at this resistor directly drives the control law function, which determines the switching frequency and the peak amplitude of the switching current. |
GND |
5 |
G |
The ground (GND) pin is both the reference pin for the controller, and the low-side return for the drive output. Special care must be taken to return all AC-decoupling capacitors as close as possible to this pin and avoid any common trace length with analog signal-return paths. |
VDD |
2 |
P |
VDD is the bias supply input pin to the device. A carefully placed bypass capacitor to GND is required on this pin. Typical bypass capacitor values are from 0.047 µF to 10 µF depending on a design. |
VS |
6 |
I |
Voltage sense (VS) is an input used to provide demagnetization timing feedback to the controller to limit frequency, to control constant-current operation, and to provide output-overvoltage detection. VS is also used for AC-mains input-voltage detection for peak primary-current compensation. This pin connects to a voltage divider between an auxiliary winding and GND. The value of the upper resistor of this divider programs the AC-mains run and stop thresholds, and factors into line compensation at the CS pin. |