TOP243F datasheet(12/52 Pages) POWERINT

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TOP242-250

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Table 3. Typical MULTI-FUNCTION Pin Configurations.

MULTI-FUNCTION PIN TABLE*

Figure Number

Three Terminal Operation

Under-Voltage

Overvoltage

Line Feed Forward (DC

MAX)

Overload Power Limiting

External Current Limit

Remote ON/OFF

Figure 11 for a description of the functions where the horizon-

tal axis (left hand side) represents the EXTERNAL CURRENT

LIMIT pin current. The meaning of the vertical axes varies

with function. For those that control the on/off states of the

output such as remote ON/OFF, the vertical axis represents the

enable/disable states of the output. For external current limit,

the vertical axis represents the magnitude of the I

LIMIT. Please

see graphs in the typical performance characteristics section

for the current limit programming range and the selection of

appropriate resistor value.

MULTI-FUNCTION (M) Pin Operation (P and G Packages)

The LINE-SENSE and EXTERNAL CURRENT LIMIT pin

functions are combined to a single MULTI-FUNCTION pin

for P and G packages. The comparator with a 1 V threshold at

the LINE-SENSE pin is removed in this case as shown in

Figure 2b. All of the other functions are kept intact. However,

since some of the functions require opposite polarity of input

current (MULTI-FUNCTION pin), they are mutually

exclusive. For example, line sensing features cannot be used

simultaneously with external current limit setting. 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 1.3 V up to a maximum current of –240

µA

(typical). At –240

µA, it turns into a constant current source.

Refer to Figure 12b.

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

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

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-GX to operate in a simple three terminal mode like

TOPSwitch-II. The MULTI-FUNCTION pin is typically used

for line sensing by connecting a resistor from this pin to the

rectified DC high voltage bus to implement OV, UV and DC

MAX

reduction with line voltage. 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 3 for possible combinations of the functions with

example circuits shown in Figure 30 through Figure 40. A

description of specific functions in terms of the MULTI-

FUNCTION pin I/V characteristic is shown in Figure 11. 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 with 30 µA

hysteresis). Between the UV and OV thresholds, the output is

enabled. For external current limit and line feed forward with

MAX reduction, the vertical axis represents the magnitude of

the I

LIMIT and DCMAX. Line feed forward with DCMAX reduction

lowers maximum duty cycle from 78% at I

M(DC) (+60 µA

typical) to 38% at I

OV (+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 programming range and the

selection of appropriate resistor value.

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

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