L6235QTR STMicroelectronics, L6235QTR Datasheet - Page 11

• Manufacturer Part Number: L6235QTR
• Description: Motor / Motion / Ignition Controllers & Drivers DMOS 3-Phase Brushless DC Motor
• Manufacturer: STMicroelectronics

Specifications of L6235QTR

• Product Category: Motor / Motion / Ignition Controllers & Drivers
• Rohs: yes

L6235Q
4.3
PWM current control
The L6235Q includes a constant OFF time PWM current controller. The current control
circuit senses the bridge current by sensing the voltage drop across an external sense
resistor connected between the source of the three lower power MOSFET transistors and
ground, as shown in
sense resistor increases proportionally. When the voltage drop across the sense resistor
becomes greater than the voltage at the reference input pin V
triggers the monostable switching the bridge off. The power MOSFET remains off for the
time set by the monostable and the motor current recirculates around the upper half of the
bridge in slow decay mode, as described in
the bridge again turns on. Since the internal dead time, used to prevent cross conduction in
the bridge, delays the turn-on of the power MOSFET, the effective OFF time t
of the monostable time plus the dead time.
Figure 10
across the sensing resistor, the pin RC voltage and the status of the bridge. More details
regarding the synchronous rectification and the output stage configuration are included in
Section
Immediately after the power MOSFET turns on, a high peak current flows through the sense
resistor due to the reverse recovery of the freewheeling diodes. The L6235 provides a 1µs
blanking time t
prematurely re-trigger the monostable.
Figure 9.
C
OFF
5V
5mA
(0)
4.4.
shows the typical operating waveforms of the output current, the voltage drop
RCOFF
R
TO GATE
OFF
(1)
LOGIC
PWM current controller simplified schematic
BLANK
2.5V
Q
+
-
Figure
that inhibits the comparator output so that the current spike cannot
R
S
MONOSTABLE
BLANKING TIME
9. As the current in the motor increases, the voltage across the
MONOSTABLE
Doc ID 018997 Rev 2
SET
1μs
COMPARATOR
SENSE
BLANKER
DEAD TIME
DRIVERS
GATE DRIVERS
Section
FROM THE
+
-
LOW-SIDE
+
R SENSE
VREF
VS
B
4.4. When the monostable times out,
SENSE B
DEAD TIME
DRIVERS
+
REF
, the sense comparator
SENSE A
Circuit description
DEAD TIME
DRIVERS
+
OFF
VS
A
is the sum
11/33
VS
OUT 2
OUT 3
OUT 1