Rev. D 10/20

9

TOP232-234

www.power.com

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

Table 2. Typical MULTI-FUNCTION Pin Configurations.

MULTI-FUNCTION PIN TABLE*

13

14

15

16

17

18

19

20

21

22

23

*This table is only a partial list of many MULTI-FUNCTION pin configurations that are possible.

Using FREQUENCY and MULTI-FUNCTIONAL Pins

FREQUENCY (F) Pin Operation

The FREQUENCY pin is a digital input pin available in TO-220

package only. Shorting the FREQUENCY pin to SOURCE pin

selects the nominal switching frequency of 132 kHz (Figure 10)

which is suited for most applications. For other cases that

may benefit from lower switching frequency such as noise

sensitive video applications, a 66 kHz switching frequency (half

frequency) can be selected by shorting the FREQUENCY pin

to the CONTROL pin (Figure 11). In addition, an example

circuit shown in Figure 12 may be used to lower the switching

frequency from 132 kHz in normal operation to 66 kHz in

standby mode for very low standby power consumption.

MULTI-FUNCTION (M) Pin Operation

When current is fed into the MULTI-FUNCTION pin, it works as

a voltage source of approximately 2.6 V up to a maximum

current of +400

µA (typical). At +400 µA, this pin turns into a

constant current sink. When current is drawn out of the

MULTI-FUNCTION pin, it works as a voltage source of

approximately 1.32 V up to a maximum current of –240

µA

(typical). At –240

µA, it turns into a constant current source.

Refer to Figure 9.

There are a total of five functions available through the use of

the MULTI-FUNCTION pin: OV, UV, line feed-forward with

DC

MAX reduction, external current limit and remote ON/OFF. A

short circuit between the MULTI-FUNCTION pin and SOURCE

pin disables all five functions and forces TOPSwitch-FX to

operate in a simple three terminal mode like TOPSwitch-II. The

MULTI-FUNCTION pin is typically used for line sensing by

Figure Number

Three Terminal Operation

Undervoltage

Overvoltage

Line Feed-forward (DC

MAX)

Line Feed-forward (I

LIMIT)

External Current Limit

Remote ON/OFF

connecting a resistor from this pin to the rectified DC high-

voltage bus to implement OV, UV and DC

MAX reduction with

line voltage functions. In this mode, the value of the resistor

determines the line OV/UV thresholds, and the DC

MAX is

reduced linearly with rectified DC high-voltage starting from

just above the UV threshold. In high efficiency applications

this pin can be used in the external current limit mode instead,

to reduce the current limit externally to a value close to the

operating peak current, by connecting the pin to the SOURCE

pin through a resistor. The same pin can also be used as a

remote on/off and a synchronization input in both modes.

Please refer to Table 2 for possible combinations of the

functions with example circuits shown in Figure 13 through

Figure 23. A description of specific functions in terms of the

MULTI-FUNCTION pin I/V characteristic is shown in Figure 8.

The horizontal axis represents MULTI-FUNCTION pin current

with positive polarity indicating currents flowing into the pin.

The meaning of the vertical axes varies with functions. For

those that control the on/off states of the output such as UV,

OV and remote ON/OFF, the vertical axis represents the enable/

disable states of the output. UV triggers at I

UV (+50 µA typical)

and OV triggers at I

OV (+225 µA typical). Between +50 µA and

+225

µA, the output is enabled. For external current limit and

line feed-forward with DC

MAX reduction, the vertical axis

represents the magnitude of the I

LIMIT and DCMAX. Line feed-

forward with DC

MAX reduction lowers maximum duty cycle

from 78% at I

M(DC) (+90 µA typical) to 38% at IOV (+225 µA).

External current limit is available only with negative MULTI-

FUNCTION pin current. Please see graphs in the typical

performance characteristics section for the current limit program-

ming range and the selection of appropriate resistor value.