E-L6205PD Datasheet, PDF (9/21 Pages) STMicroelectronics – DMOS DUAL FULL BRIDGE DRIVER

L6205
NON-DISSIPATIVE OVERCURRENT PROTECTION
The L6205 integrates an Overcurrent Detection Circuit (OCD). This circuit provides protection against a short
circuit to ground or between two phases of the bridge. With this internal over current detection, the external cur-
rent sense resistor normally used and its associated power dissipation are eliminated. Figure 7 shows a simpli-
fied schematic of the overcurrent detection 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 I_REF. When the output current in one bridge reaches the detection threshold (typically 5.6A) the relative
OCD comparator signals a fault condition. When a fault condition is detected, the EN pin is pulled below the turn
off threshold (1.3V typical) by an internal open drain MOS with a pull down capability of 4mA. By using an ex-
ternal R-C on the EN pin, the off time before recovering normal operation can be easily programmed by means
of the accurate thresholds of the logic inputs.
Figure 7. Overcurrent Protection Simplified Schematic
POWER SENSE
1 cell
OUT1_A VS_A OUT2_A
HIGH SIDE DMOSs OF
THE BRIDGE A
µC or LOGIC
+5V
R_EN EN_A
C_EN
I_1A I_2A
TO GATE
LOGIC
POWER DMOS
n cells
+
OCD
COMPARATOR
I_1A / n
INTERNAL
OPEN-DRAIN
R_DS(ON)
40Ω TYP.
(I_1A+I_2A) / n
I_REF
OVER TEMPERATURE
POWER DMOS
n cells
I_2A / n
POWER SENSE
1 cell
D02IN1353
Figure 8 shows the Overcurrent Detection operation. The Disable Time t_DISABLE before recovering normal opera-
tion 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 9. 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 10.
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 2.2KΩ to 180KΩ. Recommended values for R_EN and C_EN
are respectively 100KΩ and 5.6nF that allow obtaining 200µs Disable Time.
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