TOP232-234
Using FREQUENCY and MULTI-
FUNCTION Pins
FREQUENCY (F) Pin Operation
for line sensing by connecting a resistor from this pin to the
rectifiedDChighvoltagebustoimplementOV,UVandDCMAX
reduction with line voltage functions. In this mode, the value
of the resistor determines the line OV/UV thresholds, and the
DCMAX 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.
PleaserefertoTable2forpossiblecombinationsofthefunctions
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
thosethatcontroltheon/offstatesoftheoutputsuchasUV, OV
and remote ON/OFF, the vertical axis represents the enable/
disable states of the output. UV triggers at IUV (+50 µA typical)
and OV triggers at IOV (+225 µA typical). Between +50 µA and
+225 µA, the output is enabled. For external current limit and
line feed forward with DCMAX reduction, the vertical axis
represents the magnitude of the ILIMIT and DCMAX. Line feed
forward with DCMAX reduction lowers maximum duty cycle from
78% at IM(DC) (+90 µA typical) to 38% at IOV (+225 µA). External
currentlimitisavailableonlywithnegativeMULTI-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.
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
lowertheswitchingfrequencyfrom132kHzinnormaloperation
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
DCMAX 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
MULTI-FUNCTION PIN TABLE*
Figure Number
13
14
15
16
17
18
19
20
21
22
23
✔
Three Terminal Operation
Under-Voltage
✔
✔
✔
✔
✔
✔
✔
Overvoltage
✔
Line Feed Forward (DCMAX
)
Line Feed Forward (ILIMIT
)
✔
✔
External Current Limit
Remote ON/OFF
✔
✔
✔
✔
✔
✔
✔
✔
*This table is only a partial list of many MULTI-FUNCTION pin configurations that are possible.
Table 2. Typical MULTI-FUNCTION Pin Configurations.
B
7/01
9
PAM [ POWER ANALOG MICOELECTRONICS ]
