aoz1232-01 Alpha & Omega Semiconductor, aoz1232-01 Datasheet - Page 9

• Manufacturer Part Number: aoz1232-01
• Description: 28v/6a Synchronous Ezbucktm Regulator
• Manufacturer: Alpha & Omega Semiconductor

Detailed Description
The AOZ1232-01 is a high-efficiency, easy-to-use,
synchronous buck regulator optimized for notebook
computers. The regulator is capable of supplying 6A of
continuous output current with an output voltage
adjustable down to 0.8V. The programmable operating
frequency range of 100kHz to 1MHz enables optimizing
the configuration for PCB area and efficiency.
The input voltage of AOZ1232-01 can be as low as 2.7V.
The highest input voltage of AOZ1232-01 can be 28V.
Constant on-time PWM with input feed-forward control
scheme results in ultra-fast transient response while
maintaining relatively constant switching frequency over
the entire input range. True AC current mode control
scheme guarantees the regulator can be stable with a
ceramic output capacitor. The switching frequency can
be externally programmed up to 1MHz. Protection
features include V
current limit, output over voltage and under voltage
protection, short-circuit protection, and thermal
shutdown.
The AOZ1232-01 is available in 30-pin 5mm x 5mm QFN
package.
Input Power Architecture
The AOZ1232-01 integrates an internal linear regulator
to generate 5.3V V
than 5.3V, the linear regulator operates at low drop-
output mode; the V
minus the drop-output voltage of internal linear regulator.
Enable and Soft Start
The AOZ1232-01 has external soft start feature to limit
in-rush current and ensure the output voltage ramps up
smoothly to regulation voltage. A soft start process
begins when V
HIGH. An internal current source charges the external
soft-start capacitor; the FB voltage follows the voltage of
soft-start pin (V
is higher than 0.8V, the FB voltage is regulated by
internal precise band-gap voltage (0.8V). The soft-start
time can be calculated by the following formula:
T
If C
10nF, the soft-start time will be 3.3ms.
Constant-On-Time PWM Control with Input
Feed-Forward
The control algorithm of AOZ1232-01 is constant-on-time
PWM Control with input feed-forward.
SS
Rev. 1.0 October 2011
SS
(s) = 330 x C
is 1nF, the soft-start time will be 330µs; if C
CC
SS
) when it is lower than 0.8V. When V
CC
rises to 4.0V and voltage on EN pin is
SS
CC
CC
(nF)
under-voltage lockout, valley
from input. If input voltage is lower
voltage is equal to input voltage
SS
www.aosmd.com
is
SS
F
F
The simplified control schematic is shown below in
Figure 1.
The high-side switch on-time is determined solely by a
one-shot whose pulse width can be programmed by one
external resistor and is inversely proportional to input
voltage (IN). The one-shot is triggered when the internal
0.8V is lower than the combined information of FB
voltage and the AC current information of inductor, which
is processed and obtained through the sensed lower-side
MOSFET current once it turns on. The added AC current
information can help the stability of constant-on time
control even with pure ceramic output capacitors, which
have very low ESR. The AC current information has no
DC offset, which does not cause offset with output load
change, which is fundamentally different from other V
constant-on time control schemes.
The constant-on-time PWM control architecture is a
pseudo-fixed frequency with input voltage feed-forward.
The internal circuit of AOZ1232-01 sets the on-time of
high-side switch inversely proportional to the IN.
T
To achieve the flux balance of inductor, the buck
converter has the equation:
Once the product of V
frequency keeps constant and is independent with input
voltage.
An external resistor between the IN and TON pin sets the
switching frequency according to the following equation:
SW
ON
SW
Figure 1. Simplified Control Schematic of AOZ1232-01
PWM
=
=
=
26.3 10
--------------------------------------------------------------- -
V
---------------------------------
26.3
-------------------------- -
V
OUT
IN
Programmable
V
One-Shot
OUT



T

R
IN
ON
10
TON
V
–
IN
12
12
IN
 

V
x T
R
TON
ON
is constant, the switching
 
Comp

–
+
AOZ1232-01
Information
FB Voltage/
AC Current
Page 9 of 18
0.8V
2
(3)
(1)
(2)