ADP2450ASTZ-5-R7 datasheet(28/40 Pages) AD

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ADP2450

Data Sheet

Rev. B | Page 28 of 40

The peak inductor current (

IPEAK) is calculated with the

following equation:

PEAK

OUT





The saturation current of the inductor must be larger than the

peak inductor current. For ferrite core inductors with a quick

saturation characteristic, the saturation current rating of the

inductor must be greater than the current-limit threshold of the

switch. This greater saturation current rating prevents the

inductor from reaching saturation.

The rms current of the inductor (

IL_RMS) is calculated with the

following equation:

LRMS

OUT





Shielded ferrite core materials are recommended for low core

loss and low electromagnetic interference (EMI).

OUTPUT CAPACITOR OF BUCK REGULATOR

The output capacitor selection affects the output ripple voltage

of the buck regulator.

The output ripple is determined by the ESR and the capacitance

value. Use the following equation to select a capacitor that

meets the output ripple requirements (COUT2_RIPPLE):

OUT

RIPPLE

OUT

RIPPLE





 

where:

ΔVOUT2_RIPPLE is the allowable output ripple voltage of the buck

regulator.

OUT

RIPPLE

ESR







where RESR is the maximum equivalent series resistance of the

buck regulator output capacitor in ohms (Ω).

Select the output capacitance to be larger than COUT2_RIPPLE and

select the ESR value to be smaller than RESR to meet the output

ripple.

The selected output capacitor voltage rating must be greater

than the output voltage. The rms current rating of the output

capacitor (ICOUT2_RMS) must be greater than the value that is

calculated using the following equation:

COUT

RMS





OUTPUT VOLTAGE SETTING

Both the output voltage of boost shunt controller (VOUT1) and

buck regulator (VOUT2) are set by the external resistor dividers,

as shown in Figure 70 and Figure 71.

Boost Shunt Controller Output Voltage

The resistor values are calculated using the following equation:

1.2

TOP

OUT

BOT



 





where:

RTOP1 is the top side feedback resistor of VOUT1.

RBOT1 is the bottom side feedback resistor of VOUT1.

To limit the output voltage accuracy degradation due to the FB1

bias current (0.1 μA maximum) to less than 0.5% (maximum),

ensure that RBOT1 < 60 kΩ.

ADP2450

FB1

VOUT1

RTOP1

RBOT1

GND

Figure 70. Boost Shunt Controller Output Voltage Setting

Buck Regulator Output Voltage

The buck regulator has the following two output voltage

settings: adjustable output and fixed output.

For adjustable output voltage, connect the external resistor

divider as shown Figure 71. The resistor values are calculated

using the following equation:

0.6

TOP

OUT

BOT



 





where:

RTOP2 is the top side feedback resistor of VOUT2.

RBOT2 is the bottom side feedback resistor of VOUT2.

ADP2450

FB2

VOUT2

RTOP2

RBOT2

GND

Figure 71. Buck Regulator Adjustable Output Voltage Setting

To limit the output voltage accuracy degradation due to FB2

bias current (0.1 μA maximum) to less than 0.5% (maximum),

ensure that RBOT2 < 30 kΩ.

For fixed output voltage, connect FB2 to VOUT2 directly.

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ADP2450ASTZ-5-R7 数据表(PDF) 28 Page - Analog Devices

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