AAT4901 Datasheet, PDF (13/16 Pages) Advanced Analogic Technologies – Buffered Power Full-Bridge

FastSwitch^TM
The minimum switching frequency is chosen based on
motor characteristics (the equivalent inductance and the
parasitic series resistor) and the percentage of current
variation to the average current specified. The minimum
switching frequency is in direct proportion to the para-
sitic series resister, and in inverse proportion to the
equivalent inductance and allowable current ripple.
When driving a high-voltage DC motor, external high-
voltage MOSFETs are needed to commutate the motor.
In this application, the AAT4901 can be configured as a
double-ended gate driver, as illustrated in Figure 6.
The full-bridge power stage operates the motor drive con-
trol as shown in Figure 7. Each side of the motor can be
connected either to the battery's positive terminal or to
the battery's negative terminal through the switch. Note
that only one MOSFET on each side of the motor may be
turned on at any one time; otherwise the high-side and
low-side MOSFETs will short out the battery and burn out.
PRODUCT DATASHEET
AAT4901
Buffered Power Full-Bridge
There is also a diode connected in reverse across the field
winding, to absorb the current in the field winding when
all four MOSFETs in the bridge are turned off.
During period (A), to make the motor run forwards, Q4
is turned on, and Q1 has the PWM signal applied to it.
The current path is shown in blue in Figure 7. At period
(B) Q4 is kept on, so when the Q1 PWM signal is off, cur-
rent can continue to flow around the bottom loop through
Q3’s parasitic diode. At period (C), to make the motor
run backwards or control the speed, Q3 is turned on, and
Q2 has the PWM signal applied to it. At period (D), Q3 is
kept on, so when the Q2 PWM signal is off, current can
continue to flow around the bottom loop through Q4’s
parasitic diode. At period (E), when the motor is running
forwards for example, the motor is now acting as a gen-
erator and forcing current through its armature, through
Q2’s diode, through the battery (thereby charging the
battery) and back through Q3’s diode.
VIN: 5.0V
High-Voltage
Rail
CLK1
CLK2
C1
4.7µF/16V
1
ENA
8
N/C(END)
2
IN
7
OUTA
AAT4901-1,-2,-4
3 _ENB
(-3)
OUTB ⁶
4
N/C(ENC)
5
GND
to Motor
Figure 6: Double-Ended Gate Driver.
4901.2008.03.1.0
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