EVAL6208N Datasheet, PDF (16/27 Pages) STMicroelectronics – DMOS DRIVER FOR BIPOLAR STEPPER MOTOR

L6208
Figure 18. Wave Drive Mode
3
4
5
2
6
I_OUTA
I_OUTB
1
8
Start Up or Reset
7
CLOCK
24 6 8 2 4 6 8
D01IN1321
NON-DISSIPATIVE OVERCURRENT PROTECTION
The L6208 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 19 shows a sim-
plified 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 reaches the detection threshold (typically 5.6A) the OCD comparator signals
a fault condition. When a fault condition is detected, the EN pin is pulled below the turn off threshold (1.3V typ-
ical) by an internal open drain MOS with a pull down capability of 4mA. By using an external 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 19. Overcurrent Protection Simplified Schematic
POWER SENSE
1 cell
OUT1_A VS_A OUT2_A
HIGH SIDE DMOSs OF
THE BRIDGE A
µC or LOGIC
V_DD
R_EN. EN
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
OCD
COMPARATOR
FROM THE
BRIDGE B
D01IN1337
16/27