Datasheet

9/22
L6227
TRUTH TABLE
X = Don't care
High Z = High Impedance Output
GND (Vs) = GND during Ton, Vs during Toff
(*) Valid only in case of load connected between OUT1 and OUT2
PWM CURRENT CONTROL
The L6227 includes a constant off time PWM current controller for each of the two bridges. The current control
circuit senses the bridge current by sensing the voltage drop across an external sense resistor connected be-
tween the source of the two lower power MOS transistors and ground, as shown in Figure 7. As the current in
the load builds up the voltage across the sense resistor increases proportionally. When the voltage drop across
the sense resistor becomes greater than the voltage at the reference input (VREF
A
or VREF
B
) the sense com-
parator triggers the monostable switching the low-side MOS off. The low-side MOS remain off for the time set
by the monostable and the motor current recirculates in the upper path. When the monostable times out the
bridge will again turn on. Since the internal dead time, used to prevent cross conduction in the bridge, delays
the turn on of the power MOS, the effective off time is the sum of the monostable time plus the dead time.
Figure 7. PWM Current Controller Simplified Schematic
Figure 8 shows the typical operating waveforms of the output current, the voltage drop across the sensing re-
sistor, the RC pin voltage and the status of the bridge. Immediately after the low-side Power MOS turns on, a
high peak current flows through the sensing resistor due to the reverse recovery of the freewheeling diodes. The
L6227 provides a 1
µ s Blanking Time t
BLANK
that inhibits the comparator output so that this current spike cannot
prematurely re-trigger the monostable.
INPUTS OUTPUTS
Description (*)
EN IN1 IN2 OUT1 OUT2
L X X High Z High Z Disable
H L L GND GND Brake Mode (Lower Path)
H H L Vs GND (Vs) Forward
H L H GND (Vs) Vs Reverse
H H H Vs Vs Brake Mode (Upper Path)
DRIVERS
+
DEAD TIME
S
Q
R
DRIVERS
+
DEAD TIME
2H 1H
2L 1L
OUT2
A(or B)
SENSE
A(or B)
R
SENSE
D02IN1352
RC
A(or B)
R
C
VREF
A(or B)
I
OUT
OUT1
A(or B)
+
+
-
-
1µs
5mA
BLANKER
SENSE
COMPARATOR
COMPARATOR
OUTPUT
MONOSTABLE
RESET
2.5V
5V
FROM THE
LOW-SIDE
GATE DRIVERS
LOAD
A
(or
B
)
BLANKING TIME
MONOSTABLE
VS
A
(or B)
TO GATE LOGIC
(0) (1)