Datasheet

L6226 Circuit description
Doc ID 9452 Rev 4 13/31
4.3 Non-dissipative overcurrent detection and protection
An overcurrent detection circuit (OCD) is integrated. This circuit can be used to provides
protection against a short circuit to ground or between two phases of the bridge as well as a
roughly regulation of the load current. With this internal over current detection, the external
current sense resistor normally used and its associated power dissipation are eliminated.
Figure 9 shows a simplified schematic of the overcurrent detection circuit for the Bridge A.
Bridge B is provided of an analogous circuit.
To implement the over current detection, a sensing element that delivers a small but precise
fraction of the out-put current is implemented with each high side power MOS. Since this
current is a small fraction of the output current there is very little additional power
dissipation. This current is compared with an internal reference cur-rent IREF. When the
output current reaches the detection threshold Isover the OCD comparator signals a fault
condition. When a fault condition is detected, an internal open drain MOS with a pull down
capability of 4 mA connected to OCD pin is turned on. Figure 10 shows the OCD operation.
This signal can be used to regulate the output current simply by connecting the OCD pin to
EN pin and adding an external R-C as shown in Figure 9. The off time before recovering
normal operation can be easily programmed by means of the accurate thresholds of the
logic inputs.
I
REF
and, therefore, the output current detection threshold are selectable by RCL value,
following the equations:
● Isover = 2.8A ±30% at -25°C < Tj < 125 °C if R
CL
= 0 Ω (PROGCL connected to GND)
● Isover = 11050 / R
CL
±10% at -25 °C < T
j
< 125 °C if 5 kΩ < R
C
< 40 kΩ
Figure 11 shows the output current protection threshold versus R
CL
value in the range 5 kΩ
to 40 kΩ.
The disable time t
DISABLE
before recovering normal operation can be easily programmed by
means of the accurate
thresholds of the logic inputs. It is affected whether by C
EN
and R
EN
values and its
magnitude is reported in Figure 12. The delay time t
DELAY
before turning off the bridge when
an overcurrent has been detected depends only by C
EN
value. Its magnitude is reported in
Figure 13.
C
EN
is also used for providing immunity to pin EN against fast transient noises. Therefore
the value of C
EN
should be chosen as big as possible according to the maximum tolerable
delay time and the R
EN
value should be chosen according to the desired disable time.
The resistor R
EN
should be chosen in the range from 2.2 kΩ to 180 kΩ. Recommended
values for R
EN
and C
EN
are respectively 100 kΩ and 5.6 nF that allow obtaining 200 µs
disable time.