aoz1050pi Alpha & Omega Semiconductor, aoz1050pi Datasheet - Page 7

• Manufacturer Part Number: aoz1050pi
• Description: Ezbucktm 2 A Synchronous Buck Regulator
• Manufacturer: Alpha & Omega Semiconductor

Compared with regulators using freewheeling Schottky
diodes, the AOZ1050PI uses a freewheeling NMOSFET
to realize synchronous rectification. This greatly
improves the converter efficiency and reduces power
loss in the low-side switch.
The AOZ1050PI uses a P-Channel MOSFET as the
high-side switch. This saves the bootstrap capacitor
normally seen in a circuit using an NMOS switch. It also
allows 100 % turn-on of the high-side switch to achieve
linear regulation mode of operation. The minimum
voltage drop from V
resistance of the MOSFET plus DC resistance of the
buck inductor. It can be calculated by equation below:
where;
V
V
I
R
Output Voltage Programming
Output voltage can be set by feeding back the output to
the FB pin using a resistor divider network as shown in
Figure 1. The resistor divider network includes R
R
value and calculating the required R
below:
Some standard value of R
output voltages are listed in Table 1.
Table 1.
The combination of R
avoid drawing excessive current from the output, which
will cause power loss.
V
O
V
O_MAX
IN
DS(ON)
2
Rev. 1.0 June 2011
O
is the output current from 0 A to 2 A, and
O_MAX
. Usually, a design is started by picking a fixed R
is the input voltage from 4.5 V to 18 V,
=
V
0.8
is the maximum output voltage,
is the on resistance of the internal MOSFET.
O
0.8
1.2
1.5
1.8
2.5
3.3
5.0
(V)
=
×
⎛
⎜
⎝
V
1
IN
+
–
R
------ -
R
IN
I
1
2
O
1
⎞
⎟
⎠
to V
and R
×
R
R
1
O
1
12.7
4.99
21.5
31.1
52.3
1.0
DS ON
10
and R
(k
is the load current times DC
2
Ω
(
should be large enough to
)
2
)
for the most common
1
with the equation
R
Open
2
11.5
10.2
10
10
10
10
(k
1
Ω
and
www.aosmd.com
)
2
Since the switch duty cycle can be as high as 100 %, the
maximum output voltage can be set as high as the input
voltage minus the voltage drop on the upper PMOS and
the inductor.
Protection Features
The AOZ1050PI has multiple protection features to
prevent system circuit damage under abnormal
conditions.
Over Current Protection (OCP)
The sensed inductor current signal is also used for over
current protection. Since the AOZ1050PI employs peak
current mode control, the COMP pin voltage is
proportional to the peak inductor current. The COMP pin
voltage is limited to be between 0.4 V and 2.5 V internally.
The peak inductor current is automatically limited
cycle-by-cycle.
When the output is shorted to ground under fault
conditions, the inductor current slowly decays during a
switching cycle because the output voltage is 0 V.
To prevent catastrophic failure, a secondary current limit
is designed inside the AOZ1050PI. The measured
inductor current is compared against a preset voltage
which represents the current limit, between 3.5 A and 5.0
A. When the output current is greater than the current
limit, the high side switch will be turned off. The converter
will initiate a soft start once the over-current condition is
resolved.
Power-On Reset (POR)
A power-on reset circuit monitors the input voltage. When
the input voltage exceeds 4.1 V, the converter starts
operation. When input voltage falls below 3.7 V, the
converter will be shut down.
Thermal Protection
An internal temperature sensor monitors the junction
temperature. The sensor shuts down the internal control
circuit and high side PMOS if the junction temperature
exceeds 150 ºC. The regulator will restart automatically
under the control of the soft-start circuit when the junction
temperature decreases to 100 ºC.
AOZ1050PI
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