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DPA422RN

Highly Integrated DC-DC Converter ICs for Power over Ethernet & Telecom Applications

Power Integrations, Inc 

DPA422-426

saturation due to large load transients in forward converter

applications. DCMAX of 33% at the OV threshold was chosen to

ensure that the power capability of the 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

(typical), the CONTROL pin goes into the hysteretic mode of

operation. In this mode, the CONTROL pin goes through

alternate charge and discharge cycles between 4.8 V and 5.8 V

(see CONTROL Pin Operation section above) and the IC runs

entirely off the high-voltage DC input, but with very low power

consumption (30 mW typical at 48 V with LINE-SENSE and

EXTERNAL CURRENT LIMIT pins open). When the DPA-Switch

is remotely turned on after entering this mode, it will initiate a

normal start-up sequence with soft-start the next time the

CONTROL pin reaches 5.8 V. In the worst case, the delay from

remote on to start-up can be equal to the full discharge/charge

cycle time of the CONTROL pin, which is approximately 36 ms

for a 22 µF CONTROL pin capacitor. This reduced-consumption

remote-off mode can eliminate expensive and unreliable in-line

mechanical switches. It also allows for microprocessor-

controlled turn-on and turn-off sequences that may be required

in certain applications.

Synchronization

In addition to sensing incoming current for OV, UV and remote

ON/OFF, the LINE-SENSE pin also monitors its pin voltage

through a 1 V threshold comparator. A pin voltage below 1 V

turns on DPA-Switch. When the voltage at LINE-SENSE pin

rises beyond 1 V to disable the output, DPA-Switch completes

its current switching cycle before the output is forced off (similar

to remote ON/OFF operation). The internal oscillator is stopped

at the end of the current cycle awaiting the LINE-SENSE pin

voltage to go low to start the next cycle. This allows the use of

the 1 V threshold to synchronize DPA-Switch to an external

signal with a frequency lower than its internal switching

frequency. A transistor or an optocoupler output connected

between the LINE-SENSE pin and the SOURCE pin implements

this function (see Figure 24). Please refer to Figure 6 for the

timing waveforms of synchronization operation.

Oscillator

(SAW)

DMAX

fSYNC ≥ 128 kHz; tOFF £ 7.7 µs; 120 ns £ tON £ 2250 ns for fOSC = 400 kHz

£ 3080 ns for fOSC = 300 kHz

VL 2 V

0V

ON

Figure 6. Synchronization Timing Diagram.

tON

OFF

tOFF

SYNC

Time

PI-2762-070501

www.powerint.com

7

Rev. T 12/12

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