Rev. F 01/09

12

TOP252-262

www.powerint.com

Figure 12. MULTI-FUNCTION (P and G package). VOLTAGE MONITOR and EXTERNAL CURRENT LIMIT (Y, E/L and M package) Pin Characteristics.

-250

-200

-150

-100

-50

0

25

50

75

100

125

336

PI-4646-071708

Output

MOSFET

Switching

(Enabled)

(Disabled)

(Non-Latching)

(Latching)

Current

Limit

M Pin

V Pin

X Pin

Maximum

Duty Cycle

I

I

I

I

Pin Voltage

Note: This figure provides idealized functional characteristics with typical performance values. Please refer to the parametric

table and typical performance characteristics sections of the data sheet for measured data. For a detailed description of

each functional pin operation refer to the Functional Description section of the data sheet.

X and V Pins (Y, E, L and M Packages) and M Pin (P and G Packages) Current (

μA)

Disabled when supply

output goes out of

regulation

The circuit examples shown in Figures 41, 42 and 43 show a

simple method for implementing the primary sensed over-

voltage protection.

During a fault condition resulting from loss of feedback, output

voltage will rapidly rise above the nominal voltage. The increase

in output voltage will also result in an increase in the voltage at

the output of the bias winding. A voltage at the output of the

bias winding that exceeds of the sum of the voltage rating of the

Zener diode connected from the bias winding output to the

V-pin (or M-pin) and V-pin (or M-pin) voltage, will cause a

current in excess of I

(or M-pin), which will trigger the OVP feature.

The primary sensed OVP protection circuit shown in Figures 41,

42 and 43 is triggered by a significant rise in output voltage (and

therefore bias winding voltage). If the power supply is operating

under heavy load or low input line conditions when an open

loop occurs, the output voltage may not rise significantly.

Under these conditions, a latching shutdown will not occur until

load or line conditions change. Nevertheless, the operation

provides the desired protection by preventing significant rise in

the output voltage when the line or load conditions do change.

Primary side OVP protection with the TOPSwitch-HX in a typical

application will prevent a nominal 12 V output from rising above

approximately 20 V under open loop conditions. If greater

accuracy is required, a secondary sensed OVP circuit is

recommended.