ADP2450ASTZ-5-R7 datasheet(31/40 Pages) AD

31 / 40 page

Data Sheet

ADP2450

Rev. B | Page 31 of 40

BUCK REGULATOR OUTPUT CAPACITOR SETTING

The output of the buck regulator provides the power supply for the

PGAs, MCU, and LCD display. In most MCCB applications, the

output voltage ripple requirement is important.

To meet the output voltage ripple requirement, use the following

equations to calculate the ESR and capacitance values of the

output capacitor of buck regulator:

OUT

RIPPLE

OUT

RIPPLE







OUT

RIPPLE

ESR





This calculation results in COUT2_RIPPLE = 1.56 μF and ESR =

66 mΩ. The output capacitance must be larger than 1.56 μF, and

the output capacitor ESR value must be smaller than 66 mΩ to

meet the output voltage ripple requirement. It is recommended

to use a one piece, 10 μF ceramic capacitor (such as the

GRM21BR70J106KE76 from Murata) as the output capacitor of

the buck regulator.

VPTH RESISTOR DIVIDER SETTING

According to the system enable and disable voltage threshold

requirements, use the following equation to calculate the VPTH

resistor divider values (see Table 14 for the VSYS_RISING and

VSYS_FALLING values):

1.09 V

1.22 V

1.09 V 4.8 μA 1.22 V 1 μA

SYS RISING

SYS FALLING

TOP VP











1.22 V

4.8 μA 1.22 V

TOP VP

BOT VP

SYS RISING

TOP VP









This calculation results in RTOP_VP = 316.6 kΩ and RBOT_VP =

61.7 kΩ. Select a standard resistor value of 316 kΩ for RTOP_VP

and 61.9 kΩ for RBOT_VP.

DUMMY LOAD RESISTOR SETTING

The dummy load, together with the power detection function,

ensures that the system is not enabled until there is sufficient

current provided by the CT.

Calculate the dummy load resistor value using the following

equation:

SYS RISING

POWER

SYS MIN



This calculation results in RPOWER = 600 Ω. Choose the standard

resistor value 604 Ω for RPOWER.

Calculate the power consumption on the dummy load resistor

using the following equation (see Table 14 for the ISYS_MIN value):

DUMMY

SYS MIN

POWER



This calculation results in PDUMMY = 0.136 W. Select one 604 Ω

resistor with a 0805 package or two parallel 1.21 kΩ resistors

with 0603 packages as the dummy load.

PGA GAIN SETTING

Set the PGA gain to ×1 as a start point. According to Table 8,

connect a 42.2 kΩ resistor between the GAIN1 pin and ground.

Connect the GAIN0 pin to an input/output (I/O) pin of the

MCU. If needed, switch the PGA gain between ×1 and ×4 by

setting the GAIN0 pin to low and high, respectively.

SENSE RESISTOR SETTING

Choose a 2 Ω resistor as the sense resistor for each phase to set

the input voltage of PGA to 150 mV under the rated current, IN.

The power consumption on the sense resistor (PSENSE_MAX) when

the analog trip occurs is calculated using the following equation

(see Table 14 for the ITRP_SEC value):

SENSE MAX

TRP SEC

SENSE



where:

RSENSE is the sense resistor value.

This calculation results in PSENSE_MAX = 1.36 W. Select a 2 Ω, 2 W

resistor, such as the CRM2512-FX-2R00ELF from Bourns, as

the sense resistor.

ANALOG TRIP THRESHOLD SETTING

The PGA output voltage is a half-sinusoid waveform. Calculate

the PGA output voltage peak value (VPGA_PEAK) when the analog

trip is triggered by using the following equation:

PGA PEAK

TRP SEC

SENSE

GAIN





where GAIN = 1.

This calculation results in VPGA_PEAK = 2.333 V.

Consider that the analog trip has a default 200 μs delay time, which

results in a 3.6° phase delay of the half-sinusoid waveform. Set

the analog trip threshold voltage using the following equation:

sin86.4

TRP

PGA PEAK





This calculation results in VTRP = 2.328 V.

Calculate the trip resistor value (RTRP) using the following equation:

TRP



This calculation results in RTRP = 232.8 kΩ. Choose a standard

resistor value of 232 kΩ as the analog trip resistor.

ACTUATOR 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.

When the actuator is triggered, the instantaneous current

flowing through the MOSFET is VOUT1/RACT = 3 A. Select a

MOSFET with ID > 3 A.

The VGS voltage of the MOSFET must be higher than 5 V.

It is recommended to select the FDMC86340 from ON

Semiconductor as the actuator MOSFET.

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