ADP2450ASTZ-5-R7 datasheet(26/40 Pages) AD

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ADP2450

Data Sheet

Rev. B | Page 26 of 40

APPLICATIONS INFORMATION

OUTPUT CAPACITOR OF BOOST SHUNT

CONTROLLER

The output capacitor stores the energy coming from the CT and

provides the input voltage of the buck regulator as well as power

to the actuator. Depending on the VOUT1 setting and actuator

specification, the capacitance must be large enough so that it

can provide sufficient power to trigger the actuator when the

analog trip occurs and prevent the VOUT1 voltage from dropping.

The voltage rating of the boost shunt output capacitor must be

higher than the output voltage of the boost shunt controller

(VOUT1). A margin of at least 20% must be reserved. Polymer,

tantalum, and aluminum electrolytic capacitors are recommended

for the balance between capacitance, voltage rating, and size.

It is recommended to use a ceramic capacitor in the range from

1 μF to 10 μF in parallel with the output capacitor to reduce the

total effective series resistance (ESR), thus reducing the output

voltage ripple. Table 9 lists several recommended output

capacitors for the boost shunt controller.

Table 9. Recommended Output Capacitors

Vendor

Part Number

Capacitance

(μF)

Voltage

(V)

KEMET

T521X336M050ATE075

T521X476M035ATE070

T494E476M035AT7280

A767KN476M1HLAE029

Panasonic

EEFCX1V220R

35SVPF39M

50SVPF39M

EEHZA1H680P

EEHZA1H330XP

BRIDGE RECTIFIER

The bridge rectifier converts the sinusoid current of the CT

secondary side to a half sinusoid current to provide power to

the ADP2450. The average forward rectified current of the

bridge rectifier diode (IF) must be higher than the rms current

of the CT secondary side during normal operation. The

maximum dc blocking voltage of the bridge rectifier diode

(VDC) must be higher than the boost shunt controller output

voltage (VOUT1) of the ADP2450. Ensure that the peak forward

surge current of the bridge rectifier diode (IFSM) can handle the

peak current of the CT secondary side when a fault occurs, such

as when an analog trip is triggered.

Bridge rectifier diodes with low forward voltage are recommended.

A low forward voltage reduces the power loss on the bridge

rectifier diodes. However, the package size of the bridge rectifier

increases. Table 10 lists several recommended bridge rectifiers

for general applications.

Table 10. Recommended Bridge Rectifiers

Vendor

Part Number

IF (A)

VDC (V)

VF (V)

IFSM (A)

Bourns

CD2320-B1200

200

CD2320-B1400

400

CD2320-B1600

600

CD2320-B1800

800

CD2320-B11000

1000

Fairchild

MDB6S

600

1.1

MDB8S

800

1.1

MDB10S

1000

1.1

SENSE RESISTOR SELECTION

In a typical MCCB application, a sense resistor is connected

between the negative output of the bridge rectifier and ground

to convert the half sinusoid current signal to the half sinusoid

voltage signal as the PGA input for signal coordination. The

resistor value depends on the system rated current (IN), the turn

ratio of the current transformer, the PGA gain setting, and the

PGA output low voltage.

A large resistor value provides a large input and output voltage

signal of the PGA for easy sampling. However, a large resistor

value increases the power loss on the sense resistor. A small

resistor value reduces the power loss. However, a small resistor

value decreases the PGA input and output voltage signal. Ensure

that the lowest PGA output signal for the ADC sampling is

higher than the output low voltage of the PGA so that the

sampling accuracy of the small signal is not affected.

The resistor power must be high enough to handle the large

current flowing through the sense resistor when the analog trip

occurs. Table 11 lists several recommended sense resistors.

Table 11. Recommended Sense Resistors

Vendor

Part Number

Value (Ω)

Power (W)

Vishay Dale

WSC2515R5000FEA

0.5

WSC25151R000FEA

WSC25152R000FEA

Rohm

MCR100JZHFLR510

0.51

LTR50UZPF1R00

MCR100JZHFL2R00

Bourns

PWR2615WR500FE

0.5

CRL2512-FW-1R00ELF

CRL2512-FW-2R00ELF

CRM2512-FX-2R00ELF

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