AAT4901 Datasheet, PDF (11/16 Pages) Advanced Analogic Technologies – Buffered Power Full-Bridge

FastSwitch^TM
VIN: 2.0V ~ 5.5V
VCC
PWM1
CIN
2 -Phase
DC/DC
SW1
GND _Controller PWM2
FB
SW2
PRODUCT DATASHEET
AAT4901
Buffered Power Full-Bridge
On/Off (EN)
1
ENA
2
IN
3
ENB
4 _ENC
8
END
7
OUTA
AAT4901-3
6
OUTB
GND ⁵
L1
IL1
IL2
L2
IL1 + IL2
VOUT
R1
CO
R2
Figure 2: AAT4901 in 2-Phase Synchronous Buck Converter Power Stage.
OUTA
OUTB
IL2
IL1
IL1+IL2
Figure 3: Output Current Ripple Reduction (IL1+IL2) due to 2-Phase Cancellation.
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.
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_ON/T) is increased, the average speed of the motor
increases. Thus the speed is controlled by the duty cycle
of the PWM (Pulse Width Modulation).
4901.2008.03.1.0
www.analogictech.com
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