ADP2450ACPZ-5-R7 datasheet(30/40 Pages) AD

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ADP2450

Data Sheet

Rev. B | Page 30 of 40

DESIGN EXAMPLE

This section describes the procedures for selecting the external

components, based on a typical MCCB design example. The

system specifications are listed in Table 14. See Figure 72 for the

schematic for this design example.

Table 14. MCCB System Requirements

Parameter

Specification

Boost Shunt Controller Output Voltage

VOUT1 = 12 V

System Enable Threshold Voltage

VSYS_RISING = 9 V

System Disable Threshold Voltage

VSYS_FALLING = 7 V

Minimum System Consumption Current

ISYS_MIN = 15 mA

Buck Regulator Output Voltage

VOUT2 = 3.3 V

Buck Regulator Output Voltage Ripple

VOUT2_RIPPLE = 10 mV

Buck Regulator Output Current

IOUT2 = 100 mA

Single CT Secondary Current Under IN

(Rated Current)

IN_SEC = 75 mA

Actuator Resistance

RACT = 4 Ω

Analog Trip Current at CT Secondary Side

ITRP_SEC = 11 × IN_SEC

BOOST SHUNT OUTPUT VOLTAGE SETTING

Choose a 11.3 kΩ resistor as the bottom feedback resistor

(RBOT1), and calculate the top feedback resistor using the

following equation:

1.2

OUT

BOT

TOP

BOT





To set the output voltage of boost shunt controller to 12 V,

the resistor values are as follows: RTOP1 = 102 kΩ, and RBOT1 =

11.3 kΩ.

BOOST SHUNT OUTPUT CAPACITOR SETTING

The output capacitor of the boost shunt controller provides

energy to the actuator. The value of the capacitor depends on

the actuator specification and requirement. The capacitor value

also affects the total system start-up time. A small value

capacitor has fast system start-up time but may not provide

enough energy for the actuator when the trip occurs. A large

value capacitor has sufficient energy for the actuator but

extends the system start-up time.

A capacitor value from 100 μF to 220 μF satisfies most of the

actuator requirements in the MCCB application.

BOOST SHUNT MOSFET SETTING

The VDSS of the MOSFET must be twice as large as VOUT1 to

provide enough margin. Choose a MOSFET with VDSS > 24 V.

In a worst case scenario where the analog trip occurs on all

three phases, the current flowing through the MOSFET is 3 ×

ITRP_SEC = 2.475 A. Choose a MOSFET with ID > 3 A.

The VGS voltage of the MOSFET must be higher than 8 V.

It is recommended to select the FDMC86340 from ON

Semiconductor as the boost shunt MOSFET.

BOOST SHUNT DIODE SETTING

The VRRM of the diode must be twice as large as VOUT1 to provide

enough margin. Choose a Schottky diode with VRRM > 24 V.

The peak current rating of the diode must be higher than 3 ×

ITRP_SEC = 2.475 A to cover the worst case scenario. Choose a

Schottky diode with IO ≥ 3 A.

It is recommended to select the MBRAF360T3G from ON

Semiconductor as the boost shunt diode.

BUCK REGULATOR OUTPUT VOLTAGE SETTING

According to the system requirement, the output voltage of the

buck regulator is 3.3 V. Select the ADP2450ACPZ-1-R7 model

for a fixed 3.3 V output voltage of the buck regulator.

INDUCTOR SETTING

The peak-to-peak inductor ripple current, ΔIL, is set to 30% of

the rated output current of the buck regulator. Use the following

equation to estimate the inductor value:





OUT

LSW









where:

VIN2 = VOUT1 = 12 V.

VOUT2 = 3.3 V.

D = 0.275.

ΔIL = 0.15 A.

fSW = 1.2 MHz.

This calculation results in L = 13.3 μH. Choose the standard

inductor value of 15 μH.

The inductor peak current is calculated by using the following

equation:





15 μH

OUT

PEAK

OUT









This calculation results in IPEAK = 166 mA.

Based on the calculated current value, select an inductor with a

minimum rms current rating of 200 mA. A shield inductor is

preferred for improved system EMI performance.

It is recommended to select the LPS3015-153 from Coilcraft as

the inductor of the buck regulator.

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