6A595
8-BIT SERIAL-INPUT,
DMOS POWER DRIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
6
TEST CIRCUIT
Dwg. EP-066-2
OUT
INPUT
I
O
V
O
t
av
I
AS
= 600 mA
V
(BR)DSX
V
O(ON)
1 Ω
210 mH
+15 V
DUT
Single-pulse avalanche energy test circuit
and waveforms
E
AS
= I
AS
x V
(BR)DSX
x t
AV
/2
NORMAL LAMP IN-RUSH CURRENT
LAMP CURRENT
TIME
CURRENT LIMIT
(CHOPPING MODE)
ON ~ 40 µs
OFF ~ 2.5 ms
Dwg. WP-008-1
NOT TO SCALE
IO(chop)
CHOPPING-MODE OPERATION
High incandescent lamp turn-on currents (commonly
called in-rush currents) can contribute to poor lamp
reliability and destroy semiconductor lamp drivers.
Warming resistors protect both driver and lamp but use
significant power when the lamp is off while current-
limiting resistors waste power when the lamp is on.
Lamps with steady-state current ratings to 350 mA can be
driven by the A6A595 without the need for warming or
current limiting resistors.
As shown (the dashed line), when an incandescent
lamp is initially turned on, the cold filament is at mini-
mum resistance and will normally allow a 10x peak in-
rush current. As the lamp warms up, the filament resis-
tance increases to its rated value and the lamp current is
reduced to its steady-state rating. When switching a lamp
with the A6A595, the internal chopping circuitry limits
the current (the solid line) to I
O(chop)
. The device will stay
in the chopping mode until the lamp resistance increases
and the current requirement is less than I
O(chop)
. A side-
effect of this current-limiting feature is that lamp turn-on
time will increase.
