DPA426 Power Integrations, DPA426 Datasheet - Page 7

• Manufacturer Part Number: DPA426
• Description: (DPA423 - DPA426) Highly Integrated DC-DC Converter ICs for Distributed Power Architectures
• Manufacturer: Power Integrations

will be initiated the next time CONTROL pin voltage reaches
5.8.V. If the power supply loses regulation before reaching the
UV lower threshold, the device will enter auto-restart. At the
end of each auto-restart cycle (S7), the UV comparator is
enabled. If the UV upper threshold is not exceeded the MOSFET
will be disabled during the next cycle (see Figure 5). The UV
feature can be disabled independent of OV feature.
Line Overvoltage Shutdown (OV)
The same resistor used for UV also sets an over voltage
threshold which, once exceeded, will force the DPA-Switch
output into the off-state within one switching cycle. The ratio of
OV and UV thresholds is preset at 2.7 as can be seen in
Figure 7. When the MOSFET is off, the input voltage surge
capability is increased to the voltage rating of the MOSFET
(220 V), due to the absence of the reflected voltage and leakage
spikes on the drain. A small amount of hysteresis is provided on
the OV threshold to prevent noise triggering. The OV feature
can be disabled independent of the UV feature as shown in
Figure 13.
Line Feed Forward with DC
The same resistor used for UV and OV also implements line
voltage feed forward that minimizes output line ripple and
reduces power supply output sensitivity to line transients. This
feed forward operation is illustrated in Figure 4 by the different
values of I
higher line voltage results in smaller operating duty cycle. As
an added feature, the maximum duty cycle DC
reduced from 75% (typical) at a voltage slightly higher than the
UV threshold to 33% (typical) at the OV threshold
(see Figures 4, 7). Limiting DC
prevent transformer saturation due to large load transients in
forward converter applications. DC
threshold was chosen to ensure that the power capability of the
Figure 6. Synchronization Timing Diagram.
L
. Note that for the same CONTROL pin current,
Oscillator
(SAW)
D
MAX
V
L
2 V
0 V
MAX
MAX
Reduction
at higher line voltages helps
MAX
ON
of 33% at the OV
f
SYNC
MAX
≥ 128 kHz; t
is also
OFF
OFF
≤ 7.7 µs; 120 ns ≤ t
DPA-Switch is not restricted by this feature under normal
operation.
Remote ON/OFF
Remote ON/OFF control describes operation where the IC is
turned on or off for long periods as opposed to the cycle-by-
cycle on/off control which is described in the Synchronization
section below.
DPA-Switch can be turned on or off by controlling the current
into the LINE-SENSE pin or out from the EXTERNAL
CURRENT LIMIT pin (see Figure 7). This allows easy
implementation of remote ON/OFF control of DPA-Switch in
several different ways. A transistor or an optocoupler output
connected between the EXTERNAL CURRENT LIMIT pin
and the SOURCE pin implements this function with “active-
on” (Figures 17, 19 and 21) while a transistor or an optocoupler
output connected between the LINE-SENSE pin and the
CONTROL pin implements the function with “active-off”
(Figures 18, 20 and 22).
When a signal is received at the LINE-SENSE pin or the
EXTERNAL CURRENT LIMIT pin to disable the output
through any of the pin functions such as OV, UV and remote
ON/OFF, DPA-Switch always completes its current switching
cycle before the output is forced off. The internal oscillator is
stopped at the end of the current cycle and stays there as long as
the disable signal exists. When the signal at the above pins
changes state from disable to enable, the internal oscillator
starts the next switching cycle.
The remote ON/OFF feature can be used as a standby or power
switch to turn off the DPA-Switch and keep it in a very low
power consumption state for indefinitely long periods. If the
DPA-Switch is held in remote-off state for longer than 10 µs
t
ON
t
OFF
ON
≤ 2250 ns for f
≤ 3080 ns for f
SYNC
OSC
OSC
= 400 kHz
= 300 kHz
DPA423-426
Time
PI-2762-070501
1/04
K
7