TOP250 datasheet(11/54 Pages) POWERINT

11 / 54 page

Rev. R 10/20

TOP242-250

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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 with 30 µA hysteresis) and

OV triggers at I

OV (+225 µA typical with 8 µA hysteresis).

Between the UV and OV thresholds, the output is enabled.

For line feed-forward with DC

MAX reduction, the vertical axis

represents the magnitude of the DC

MAX. Line feed-forward

with DC

MAX reduction lowers maximum duty cycle from 78%

at I

L(DC) (+60 µA typical) to 38% at IOV (+225 µA).

EXTERNAL CURRENT LIMIT (X) Pin Operation

(Y, R and F Packages)

When current is drawn out of the EXTERNAL CURRENT

LIMIT 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 12a).

There are two functions available through the use of the

EXTERNAL CURRENT LIMIT pin: external current limit

and remote ON/OFF. Connecting the EXTERNAL

CURRENT LIMIT pin to the SOURCE pin disables the two

functions. In high efficiency applications, this pin can be

used 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 pin can also be

used for remote ON/OFF. Table 2 shows several possible

combinations using this pin. See Figure 11 for a description

of the functions where the horizontal 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 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-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 increasing rectified

DC high voltage starting from just above the UV threshold.

External current limit programming is implemented by

connecting the MULTI-FUNCTION pin to the SOURCE pin

Table 3. Typcial MULTI-FUNCTION Pin Configurations.

MULTI-FUNCTION PIN TABLE*

Figure Number

Three Terminal Operation

Undervoltage

Overvoltage

Line Feed-Forward (DC

MAX)

Overload Power Limiting

External Current Limit

Remote ON/OFF

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

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