AOZ1110QI Alpha & Omega Semiconductor Inc, AOZ1110QI Datasheet - Page 12

• Manufacturer Part Number: AOZ1110QI
• Description: IC BUCK SYNC ADJ 4A 24QFN
• Manufacturer: Alpha & Omega Semiconductor Inc
• Series: EZBuck™r
• Type: Step-Down (Buck), PWM - Current Moder

Specifications of AOZ1110QI

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 V ~ 5.5 V
• Current - Output: 4A
• Frequency - Switching: 500kHz, 1MHz
• Voltage - Input: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-WFQFN Exposed Pad
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 785-1257-2

Thermal Management and Layout
Consideration
In the AOZ1110QI buck regulator circuit, high pulsing
current flows through two circuit loops. The first loop
starts from the input capacitors, to the VIN pin, to the LX
pins, to the filter inductor, to the output capacitor and
load, and then return to the input capacitor through
ground. Current flows in the first loop when the high side
switch is on. The second loop starts from inductor, to the
output capacitors and load, to the low-side N-MOSFET.
Current flows in the second loop when the low side N-
MOSFET is on.
In PCB layout, minimizing the two loops area reduces the
noise of this circuit and improves efficiency. A ground
plane is strongly recommended to connect input
capacitor, output capacitor, and PGND pin of the
AOZ1110QI.
In the AOZ1110QI buck regulator circuit, the major power
dissipating components are the AOZ1110QI and the
output inductor. The total power dissipation of converter
circuit can be measured by input power minus output
power:
The power dissipation of inductor can be approximately
calculated by output current and DCR of inductor:
The actual junction temperature can be calculated with
power dissipation in the AOZ1012D and thermal
impedance from junction to ambient:
The maximum junction temperature of AOZ1110QI is
150ºC, which limits the maximum load current capability.
The thermal performance of the AOZ1110QI is strongly
affected by the PCB layout. Extra care should be taken
by users during design process to ensure that the IC will
operate under the recommended environmental
conditions.
P
T
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total_loss
junction
Rev. 1.0 October 2010
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I
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IN
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www.aosmd.com
Several layout tips are listed below for the best electric
and thermal performance.
1. The LX pins are connected to internal P-MOSFET
2. Do not use thermal relief connection to the VIN and
3. Input capacitor should be connected to the VIN pin
4. A ground plane is preferred. If a ground plane is not
5. Make the current trace from LX pins to L to Co to the
6. Pour copper plane on all unused board area and
7. Keep sensitive signal trace far away form the LX
and N-MOSFET drains. They are low resistance
thermal conduction path and most noisy switching
node. Connect a large copper plane to LX pin to help
thermal dissipation. For full load (4A) application,
also connect the LX pads to the bottom layer by
thermal vias to enhance the thermal dissipation.
the PGND pin. Pour a maximized copper area to the
PGND pin and the VIN pin to help thermal
dissipation.
and the PGND pin as close as possible.
used, separate PGND from AGND and connect them
only at one point to avoid the PGND pin noise
coupling to the AGND pin.
PGND as short as possible.
connect it to stable DC nodes, like VIN, GND or
VOUT.
pins.
Page 12 of 16
AOZ1110