TOP243F datasheet(11/52 Pages) POWERINT

11 / 52 page

TOP242-250

1/02

FREQUENCY (F) Pin Operation

The FREQUENCY pin is a digital input pin available in the

Y, R or F package only. Shorting the FREQUENCY pin to

SOURCE pin selects the nominal switching frequency of

132 kHz (Figure 13) 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 14). In addition, an example circuit shown in Figure 15

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.

LINE-SENSE (L) Pin Operation (Y, R and F Packages)

When current is fed into the LINE-SENSE 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. Refer to Figure 12a. In addition, a

comparator with a threshold of 1 V is connected at the pin and is

used to detect when the pin is shorted to the SOURCE pin.

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

the LINE-SENSE pin: OV, UV, line feed forward with DC

MAX

reduction, and remote ON/OFF. Connecting the LINE-SENSE

pin to the SOURCE pin disables all four functions. The LINE-

SENSE pin is typically used for line sensing by connecting a

resistor from this pin to the rectified DC high voltage bus to imple-

ment OV, UV and DC

MAX reduction with line voltage. In this

mode, the value of the resistor determines the line OV/UV thresh-

olds, and the DC

MAX is reduced linearly with rectified DC high

voltage starting from just above the UV threshold. The pin can

also be used as a remote on/off and a synchronization input. Refer

to Table 2 for possible combinations of the functions with

Using Feature Pins

✔

✔✔

✔

✔✔

✔

✔✔

✔

✔✔

✔

✔✔

✔

✔✔

✔

Table 2. Typical LINE-SENSE and EXTERNAL CURRENT LIMIT Pin Configurations.

*This table is only a partial list of many LINE-SENSE and EXTERNAL CURRENT LIMIT pin configurations that are possible.

Figure Number

Three Terminal Operation

Under-Voltage

Overvoltage

Line Feed Forward (DC

MAX)

Overload Power Limiting

External Current Limit

Remote ON/OFF

example circuits shown in Figure 16 through Figure 40. A

description of specific functions in terms of the LINE-SENSE

pin I/V characteristic is shown in Figure 11 (right hand side).

The horizontal axis represents LINE-SENSE 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

with 30

µA hysteresis) and OV triggers at I

OV (+225 µA

typical with 8

µA hysteresis). Between the UV and OV thresh-

olds, the output is enabled. For line feed forward with DC

MAX

reduction, the vertical axis represents the magnitude of the

MAX. Line feed forward with DCMAX reduction lowers

maximum duty cycle from 78% at I

L(DC) (+60 µA typical) to

38% at I

OV (+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 and 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 as a remote on/off. Table 2

shows several possible combinations using this pin. See

LINE-SENSE AND EXTERNAL CURRENT LIMIT PIN TABLE*

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