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A7122 Datasheet(PDF) 9 Page - AIT Components Ltd.

No. de Pieza. A7122
Descripción  DC-DC CONVERTER BUCK SYNCHRONOUS BUCK CONVERTER
Descarga  13 Pages
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Fabricante  AITCOMPONENTS [AIT Components Ltd.]
Página de inicio  http://aitcomponents.com
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A7122 Datasheet(HTML) 9 Page - AIT Components Ltd.

 
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AiT Semiconductor Inc.
www.ait-ic.com
A7122
DC-DC CONVERTER BUCK (STEP-DOWN)
2A 3MHz 6V SYNCHRONOUS BUCK CONVERTER
REV1.1
- JUL 2012 RELEASED, DEC 2014 UPDATED -
- 9 -
Soft Start
A7122 has a internal soft-start circuitry to reduce supply inrush current during startup conditions. When the
device exits under-voltage lockout (UVLO), shutdown mode, or restarts following a thermal-overload event,
the l soft-start circuitry slowly ramps up current available at SW.
UVLO and Thermal Shutdown
If VIN drops below 2V, the UVLO circuit inhibits switching. Once VIN rises above 2.1V, the UVLO clears, and
the soft-start sequence activates. Thermal-overload protection limits total power dissipation in the device.
When the junction temperature exceeds TJ
= +160°C, a thermal sensor forces the device into shutdown,
allowing the die to cool. The thermal sensor turns the device on again after the junction temperature cools by
15°C, resulting in a pulsed output during continuous overload conditions. Following a thermal-shutdown
condition, the soft-start sequence begins.
DESIGN PROCEDURE
Inductor Selection
The peak-to-peak ripple is limited to 30% of the maximum output current. This places the peak current far
enough from the minimum overcurrent trip level to ensure reliable operation while providing enough current
ripples for the current mode converter to operate stably. In this case, for 2A maximum output current, the
maximum inductor ripple current is 667 mA. The inductor size is estimated as following equation:
LIDEAL=(VIN(MAX)-VOUT)/IRIPPLE*DMIN*(1/FOSC)
Therefore,
for VOUT=1.8V, t
he inductor values is calculated to be L = 0.60μH. Choose 1μH
And for VOUT =1.2V, t
he inductor values is calculated to be L = 0.469μH. Choose 0.47μH
The resulting ripple is
IRIPPLE =(VIN(MAX)-VOUT)/LACTUAL*DMIN*(1/FOSC)
When,
VOUT=1.8V, IRIPPLE=403mA
VOUT=1.2V, IRIPPLE=665mA
Output Capacitor Selection
For most applications a nominal 10μF or 22μF capacitor is suitable. The A7122 internal compensation is
designed for a fixed corner frequency that is equal to


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