AAT4901IJS-1-T1 ANALOGICTECH [Advanced Analogic Technologies], AAT4901IJS-1-T1 Datasheet - Page 11

• Manufacturer Part Number: AAT4901IJS-1-T1
• Description: Buffered Power Full-Bridge
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

When the voltage applied between the DC motor by the
input(s) logic control is reversed, it could change the
rotation direction. When both outputs (OUTA/OUTB) are
floating, the motor winding acts as a regeneration; the
current inside the motor winding would continue to flow
into the input capacitor through the internal MOSFET
parasitic diode and decay to zero rapidly, stopping the
motor rapidly. When both outputs are connected to the
input supply (or ground) simultaneously, the motor
coasts and the winding current decays slowly due to the
winding resistor until the motor free runs to a stop.
The speed of a DC motor is directly proportional to the
supply voltage. It can be controlled by simply adjusting
the voltage sent to the motor, but this is quite inefficient.
FastSwitch
4901.2008.03.1.0
Figure 3: Output Current Ripple Reduction (IL1+IL2) due to 2-Phase Cancellation.
V
TM
IN
: 2.0V ~ 5.5V
OUTA
OUTB
IL2
IL1
IL1+IL2
Figure 2: AAT4901 in 2-Phase Synchronous Buck Converter Power Stage.
C
IN
VCC
GND
FB
Controller
2 -Phase
DC/DC
PWM1
PWM2
SW1
SW2
w w w . a n a l o g i c t e c h . c o m
On/Off (EN)
1
2
3
4
ENA
ENB
ENC
IN
AAT4901-3
A better method is to switch the motor’s supply on and off
rapidly. If the switching is fast enough, the motor doesn’t
notice it, it only notices the average effect. The time it
takes a motor to speed up and slow down under switching
conditions is dependent on the inertia of the rotor (basi-
cally how heavy it is) and the amount of friction and load
torque. Figure 5 shows the speed of a motor that is being
turned on and off at a fairly low switching frequency. The
average speed is around 150, although it varies quite a
bit. If the supply voltage is switched quickly enough, the
motor will not have time to change speed much and the
speed will be quite steady. When the duty cycle (D =
T
increases. Thus the speed is controlled by the duty cycle
of the PWM (Pulse Width Modulation).
ON
/T) is increased, the average speed of the motor
OUTA
OUTB
GND
END
8
7
6
5
IL1
IL2
Buffered Power Full-Bridge
PRODUCT DATASHEET
L1
L2
R1
R2
IL1 + IL2
AAT4901
C
O
V
OUT
11