Datasheet

L9935 Functional description
Doc ID 5198 Rev 10 13/29
5.2 Full bridge function
Figure 5. Displays a full bridge including the current sense circuit.
5.2.1 No current
Bit 5, bit 4 (corresponding bit 2 and bit1 for bridge B) both are HIGH, the current logic will
inhibit all drivers D
11
, D
12
, D
21
, D
22
turning off M
11
, M
12
, M
21
, M
22
independently from the
signal of the current sense comparator comp 1.
5.2.2 Turning on
Changing bit 5 or bit 4 or both to LOW will turn on either M
11
and M
22
or M
21
and M
12
(depending on the phase signal bit 3). Current will start to flow through the load. The current
will be sensed by the drop across R
1
.
The threshold of the comparator comp 1 depends on the current settings of bit 5 and bit 4.
The current will rise until it exceeds the turn off threshold of comp 1.
5.2.3 Chopping
Exceeding the threshold of comp 1 the drive logic will turn off the sink transistor (M
12
or
M
22
). The sink transistor periodically is turned on again by the oscillator. Immediately after
turning on M
12
or M
22
the comparator comp 1 will be inhibited for a certain time to blank
switch over spikes caused by capacitive load components up to 5 nF.
Turning off for example M
12
will yield a flyback current through D
11
. (So now the free
wheeling current flows through M
21
, the load and D
11
).
This leads to a slow current decay during flyback. Maximum duty cycles of more than 85%
(at f
OSC
= 25 kHz) are possible. In this case current flows of both bridges will overlap (not
shown in Figure 7).
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