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9

IRPLDIM2U

Receive signal

RB1

RB0

Communications-enable

Receive-drive signal

Fig. 8 Dali and Micro-Conttoller signals

Shutdown and Low Power

With shutdown there are some unique power conditions. With the shutdown line low and the lamp ignited, the

PIC16F628 derives its power from the charge pump of the IR21592. The charge pump provides enough current

Fig. 9 Communications signal with the lamp off

Receive signal

RB1

RB0

Communications-enable

Receive-drive signal

SD pin IR21592

LO pin IR21592

for the microcontroller to run at its internal frequency of

4MHz during normal operation. When the shutdown

line is asserted the IR21592 is disabled, and the charge

pump is no longer functioning. Current is drawn directly

from the high voltage DC line through a high value re-

sistor. The micro controller is put to sleep during this

time to minimize current draw and power dissipation.

To receive data, which requires significant current, the

PIC16F628 wakes up and starts the charge pump of

the IR21592 long enough to process the command, typi-

cally less than 25ms, but not long enough to ignite the

lamp (see waveforms in Figure 9). Doing this unique

management minimizes power dissipation during shut-

down.