1

Pin setting

Figure 1. Connection diagram

GND

N.C.

OVP

N. A.

UVP

VCC

N. C.

N. C.

N. C.

N. C.

DRAIN

DRAIN

DRAIN

DRAIN

FB

COMP

Table 1. Pin description

Pin

number

Name

Function

1

GND

Ground and MOSFET source. Connection of both the source of the internal MOSFET and the return of

the bias current of the device. All of the groundings of bias components must be tied to a trace going to

this pin and kept separate from the pulsed current return.

2

N. C.

Not connected. When designing the PCB, this pin can be soldered to GND.

3

VCC

Controller Supply. An external storage capacitor has to be connected across this pin and GND. The

pin, internally connected to the high-voltage current source, provides the VCC capacitor charging current

at startup. A small bypass capacitor (0.1 μF typ.) in parallel, placed as close as possible to the IC, is also

recommended, for noise filtering purposes.

4

N.A.

Not available for user. This pin is mechanically connected to the controller die pad of the frame. In order

to improve noise immunity, it is highly recommended to connect it to GND.

5

UVP

Undervoltage Protection. If VUVP falls below the internal threshold VUVP_th (0.4 V typ.) for more than

tUVP_DEB time (30 ms, typ.), the IC is disabled, and its consumption reduced to ultra-low values. When

VUVP rises above VUVP_th, the device waits for a tUVP_REST time interval (30 ms, typ.) then resumes

switching. The pin can be used to realize an input undervoltage protection or as a disabling input for the

entire SMPS, with ultra-low residual input power consumption. If the feature is not required, the pin must

be left open, which excludes the function.

6

OVP

Overvoltage protection. If VOVP exceeds the internal threshold VOVP_th (4 V typ.) for more than

tOVP_DEB time (250 μsec, typ.), the PWM is disabled in auto-restart for tOVP_REST (500 msec, typ.) until

the OVP condition is removed, after that it restarts switching with soft-start phase. OVP pin can be used

to realize an input overvoltage protection (or, in non-isolated topologies, an output overvoltage

protection).

If the feature is not required, the pin must be connected to GND, which excludes the function.

7

FB

Direct feedback. It is the inverting input of the internal transconductance E/A, internally referenced to

1.2 V with respect to GND. In non-isolated converter, the output voltage information is directly fed into the

pin through a voltage divider. In primary regulation, the FB voltage divider is connected to the VCC. The

E/A is disabled if FB is connected to GND.

8

COMP

Compensation. This is the output of the internal E/A. A compensation network is placed between this

pin and GND to achieve stability and good dynamic performance of the control loop. In case of

secondary feedback, the internal E/A must be disabled and the COMP directly driven by the optocoupler

to control the DRAIN peak current setpoint.

9 to 12

N.C.

Not connected. These pins must be left floating in order to get a safe clearance distance.

VIPER31

Pin setting

DS13285 - Rev 6

page 2/39