Datasheet

APPLICATION CIRCUIT
D2, D4 = 2A High speed diodes
D1, D3 = 1A High speed diodes
R1 = R2 = 2Ω
L1 = L2 = 5 mH
)
trr ≤ 200 ns
FUNCTIONAL DESCRIPTION
The L295 incorporates two indipendent driver
channals with separate inputs and outputs, each
capable of driving an inductive load (see block
diagram).
The device is controlled by three micriprocessor
compatible digital inputs and two analoginputs.
These inputs are:
EN chip enable (digital input, active low),
enables both channelswhen in thelow
state.
V
in1
,V
in2
channel inputs (digital inputs, active
high), enable each channel inde-
pendently. A channel is actived when
both EN and the appropriate channel
input are active.
V
ref1
,V
ref2
referce voltages (analog inputs), used
to program the peak load currents.
Peak loadcurrentis proportionalto V
ref
.
Since the two channelsare identical, only channel
one will be described.
The following description applies also the channel
two, replacing FF2 for FF1, V
ref
for V
ref1
etc.
When the channel is avtivated by low level on the
EN input anda high level on the channelinput, V
in2
,
the output transistors Q1 and Q2 switch on and
current flowsin the load according to the exponen-
tial law:
I =
V
R1
( 1 − e
− R1 t
L1
)
where: R1 and R2 are the resistance and in-
ductanceof the load and V is the volt-
age available on the load (V
s
-V
drop
-
V
sense
).
The current increases until the voltage on the ex-
ternal sensingresistor, R
S1
, reaches the reference
voltage, V
ref1
. This peak current, I
p1
, is given by:
I
p1
=
V
ref1
R
S1
At this point the comparator output, Vomp1, sete
the RS flip-flop, FF1, that turns off the output tran-
sistor, Q1.The load current flowing throughD2,Q2,
R
S1
, decreases according to the law:
I =(
V
A
R
1
+I
p1
) e
− R1 t
L1
−
V
A
R1
where V
A
=V
CEsat Q2
+V
sense
+V
D2
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L295