TOP243YN datasheet(11/52 Pages) POWERINT

11 / 52 page

TOP242-250

12/04

MAX reduction, the vertical axis represents the magnitude of

the DC

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 EXTERNALCURRENT

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 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-FUNCTIONpin),theyaremutuallyexclusive.

Forexample,linesensingfeaturescannotbeusedsimultaneously

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

MAX reduction with line voltage. In this mode, the value

of the resistor determines the line OV/UV thresholds, and the

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-FUNCTIONpintotheSOURCEpinthrougharesistor.

However, this function is not necessary in most applications

since the internal current limit of the P and G package devices

has been reduced, compared to the Y, R and F package

devices, to match the thermal dissipation capability of the P

and G packages. It is therefore recommended that the MULTI-

FUNCTION pin is used for line sensing as described above and

not for external current limit reduction. The same pin can also

Table 3. Typcial 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

✓

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

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