DPA423 Power Integrations, Inc., DPA423 Datasheet - Page 9

• Manufacturer Part Number: DPA423
• Description: Highly Integrated DC-DC Converter Ics For Distributed Power Architecturesthe Dpa-switch ic Family Introduces a Highly Integratedsolution For DC-DC Conversion Applications in The 16-75 Vdcinput Range.dpa-switch Uses The Same Proven Topology as Topswit
• Manufacturer: Power Integrations, Inc.

Using Feature Pins
FREQUENCY (F) Pin Operation
The FREQUENCY pin is a digital input pin. Shorting the
FREQUENCY pin to SOURCE pin selects the nominal
switching frequency of 400 kHz (Figure 9) which is suited for
most applications. For other applications that may benefit from
lower switching frequency, a 300 kHz switching frequency can
be selected by shorting the FREQUENCY pin to the CONTROL
pin (Figure 10). This pin should not be left open.
LINE-SENSE (L) Pin Operation
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 +240 µA (typical). At +240 µA, this pin turns into a constant
current sink. Refer to Figure 8. 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 five functions available through the use of
the LINE-SENSE pin: OV, UV, line feed forward with DC
reduction, remote ON/OFF and synchronization. Shorting the
LINE-SENSE pin to the SOURCE pin disables all five functions.
The LINE-SENSE pin is typically used for line sensing by
connecting a resistor from this pin to the positive input DC
voltage bus to implement OV, UV and line feed forward with
DC
resistor determines the line OV/UV thresholds, and the DC
is reduced linearly with input DC high voltage starting from just
above the UV threshold. This pin can also be used as the input
pin for remote ON/OFF and synchronization. An external
transistor placed between the LINE-SENSE pin and the
CONTROL pin realizes remote on/off via UV or OV threshold.
Synchronization is available by connecting an open drain
external MOSFET between the LINE-SENSE pin and the
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.
Three Terminal Operation
Under-Voltage
Overvoltage
Line Feed Forward (DC
Overload Power Limiting
External Current Limit
Remote ON/OFF
Synchronization
MAX
reduction over line voltage. In this mode, the value of the
Figure Number
LINE-SENSE AND EXTERNAL CURRENT LIMIT PIN TABLE*
MAX
)
11
12
13
14
MAX
MAX
15
SOURCE pin to generate synchronization pulse. Each time the
MOSFET turns on, the falling edge of the LINE-SENSE pin
voltage initiates a new switching cycle. The lowest
synchronization frequency guaranteed by DPA-Switch is
128 kHz. Refer to Table 2 for possible combinations of the
functions with example circuits shown in Figure 11 through
Figure 24. A description of specific functions in terms of the
LINE-SENSE pin I/V characteristic is shown in Figure 7 (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
with 4 µA hysteresis) and OV triggers at I
with 4 µA hysteresis). Between the UV and OV thresholds, the
output is enabled. For line feed forward with DC
the vertical axis represents the magnitude of the DC
forward with DC
75% at I
EXTERNAL CURRENT LIMIT (X) Pin Operation
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 -230 µA (typical). At -230 µA, it
turns into a constant current source (refer to Figure 8).
There are two functions available through the use of the
EXTERNAL CURRENT LIMIT pin: external current limit and
remote ON/OFF. Shorting the EXTERNAL CURRENT LIMIT
pin and SOURCE pin disables both 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 control input. Table 2
16
L(DC)
17
(+55 µA typical) to 33% at I
MAX
18
reduction lowers maximum duty cycle from
19
20
21
DPA423-426
OV
OV
(+135 µA).
22
UV
(+135 µA typical
(+50 µA typical
MAX
MAX
23
4/04
reduction,
Line feed
L
24
9