AOZ1019AI 데이터 시트보기 (PDF) - Alpha and Omega Semiconductor
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AOZ1019AI Datasheet PDF : 14 Pages
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AOZ1019
Detailed Description
The AOZ1019 is a current-mode step down regulator with
integrated high side PMOS switch. It operates from a
4.5V to 16V input voltage range and supplies up to 2A of
load current. The duty cycle can be adjusted from 6% to
100% allowing a wide range of output voltage. Features
include enable control, Power-On Reset, input under
voltage lockout, fixed internal soft-start and thermal shut
down.
The AOZ1019 is available in SO-8 package.
Enable and Soft Start
The AOZ1019 has an internal 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 the input voltage rises to 4.0V and voltage
on EN pin is HIGH. In soft start process, the output
voltage is ramped to regulation voltage in typically 2.2ms.
The 2.2ms soft start time is set internally.
The EN pin of the AOZ1019 is active HIGH. Connect the
EN pin to VIN if enable function is not used. Pulling EN to
ground will disable the AOZ1019. Do not leave it open.
The voltage on EN pin must be above 2.0 V to enable the
AOZ1019. When voltage on EN pin falls below 0.6V, the
AOZ1019 is disabled. If an application circuit requires the
AOZ1019 to be disabled, an open drain or open collector
circuit should be used to interface to the EN pin.
Steady-State Operation
Under steady-state conditions, the converter operates in
fixed frequency and Continuous-Conduction Mode
(CCM).
The AOZ1019 integrates an internal P-MOSFET as the
high-side switch. Inductor current is sensed by amplifying
the voltage drop across the drain to source of the high
side power MOSFET. Output voltage is divided down by
the external voltage divider at the FB pin. The difference
of the FB pin voltage and reference is amplified by the
internal transconductance error amplifier. The error volt-
age, which shows on the COMP pin, is compared against
the current signal, which is sum of inductor current signal
and ramp compensation signal, at PWM comparator
input. If the current signal is less than the error voltage,
the internal high-side switch is on. The inductor current
flows from the input through the inductor to the output.
When the current signal exceeds the error voltage, the
high-side switch is off. The inductor current is freewheel-
ing through the internal Schottky diode to output.
The AOZ1019 uses a P-Channel MOSFET as the high
side switch. It saves the bootstrap capacitor normally
seen in a circuit using an NMOS switch. It allows 100%
turn-on of the upper switch to achieve linear regulation
mode of operation. The minimum voltage drop from VIN to
VO is the load current x DC resistance of MOSFET +
DC resistance of buck inductor. It can be calculated by
equation below:
V O_MAX = V IN – I O × (R DS(ON ) + R inductor )
where;
VO_MAX is the maximum output voltage,
VIN is the input voltage from 4.5V to 16V,
IO is the output current from 0A to 2A,
RDS(ON) is the on resistance of internal MOSFET, the value is
between 97mΩ and 200mΩ depending on input voltage and
junction temperature, and
Rinductor is the inductor DC resistance.
Switching Frequency
The AOZ1019 switching frequency is fixed and set by an
internal oscillator. The actual switching frequency ranges
from 400kHz to 600kHz due to device variation.
Output Voltage Programming
Output voltage can be set by feeding back the output to
the FB pin with a resistor divider network as shown in
Figure 1. The resistor divider network includes R2 and
R3. Typically, a design is started by picking a fixed R3
value and calculating the required R2 with equation below.
VO
=
0.8
×
1
+
R-----2-
R3
Some standard value of R2, R3 for most commonly used
output voltage values are listed in Table 1.
Table 1.
VO (V)
0.8
1.2
1.5
1.8
2.5
3.3
5.0
R2 (kΩ)
1.0
4.99
10
12.7
21.5
31.6
52.3
R3 (kΩ)
Open
10
11.5
10.2
10
10
10
Rev. 1.0 September 2007
www.aosmd.com
Page 6 of 14
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