Datasheet

If the oscillator pin (9) is connected to ground the
load current falls to zero as shown in fig. 1.
At this time t
2
the channel 1 is disabled, by taking
the inputs V
in1
low and/or EN high, and the output
transistor Q2 is turned off. The load current flows
through D2 and D1 according to the law:
I =(
V
B
R
1
+I
T2
) e
− R1 t
L1
−
V
B
R1
where V
B
=V
S
+V
D1
+V
D2
I
T2
= current value at the time t
2
.
Fig. 2 in shows the current waveform obtained with
an RC network connected between pin 9 and
ground. From to t
1
the current increases as in fig.
1. A difference exists at the time t
2
because the
current starts to increase again. At this time a pulse
is producedby the oscillator circuit that resets the
flip.flop, FF1, and switcheson the outout transistor,
Q1. The current increases until the drop on the
sensing resistor R
S1
is equal to V
ref1
(t
3
) and the
cycle repeats.
SIGNAL WAVEFORMS
The switching frequency depends on the value R
and C, as shown in fig. 4 and must be chosen in
the range 10 to 30 KHz.
It is possible with external hardwareto change the
referencevoltageV
ref
inorder to obtaina highpeak
current I
p
anda lower holding currentI
h
(see fig. 3).
The L295is provided with a thermal protection that
switches off all the output transistors when the
junction temperature exceeds 150°C. The pres-
ence of ahysteresiscircuitmakestheIC workagain
aftera fall of the junction temperature of about
20°C.
The analoginputpins (V
ref1
,V
ref2
) can be left open
or connectedto V
ss
; in this case the circuit works
with aninternalreferencevoltageofabout2.5Vand
the peakcurrent in theloadis fixedonlybythe value
of R
s
:
I
p
=
2.5
R
S
Figure 1. Load current waveform with pin 9
connected to GND.
Figure 2. Load current waveform with external
R-C network connected between pin 9 and
ground.
5/8
L295