ADP2450ASTZ-5-R7 datasheet(24/40 Pages) AD

24 / 40 page

ADP2450

Data Sheet

Rev. B | Page 24 of 40

OPERATIONAL AMPLIFIER

The operational amplifier is a low offset amplifier. The amplifier

is used for leakage current detection in circuit breaker application.

Figure 67 shows the circuit configuration with the operational

amplifier for leakage current detection as well as R1 and R2. The

output voltage of the operational amplifier is calculated with the

following equation:

REF

EOUT

ZCT





where:

VEOUT5 is the voltage on the EOUT5 pin.

VREF is the external reference voltage.

ILK is the leakage current.

N is the turn ratio of the zero-current transformer (ZCT).

RZCT is the current sense resistor at the secondary side of the ZCT.

EA5

EIN5_N

EIN5_P

ADP2450

EOUT5

VREF

2R2

RZCT

2R2

ZCT

1:N

ILK

–

Figure 67. Typical Configuration for Leakage Current Detection

ANALOG TRIP PROTECTION

The ADP2450 integrates an analog trip circuit for fast

protection in circuit breaker applications. The analog trip

circuit monitors the output of each PGA. When any of the four

PGA outputs exceeds the analog trip threshold, VTRP or VTRPL,

for the deglitch time, tTRP, the analog trip protection is triggered.

Two programmable analog trip thresholds, VTRP and VTRPL,

support both half-sinusoid and bipolar sinusoid input signal

application. VTRP is the high threshold and VTRPL is the low

threshold. The PGAx output signal is compared with the two

analog trip thresholds. If the PGAx output signal is either

higher than VTRP or lower than VTRPL, the analog trip protection

is triggered as shown in Figure 68.

AVDD

EINx

ADP2450

INPUT

SIGNAL

PGAx

VTRP

VCOM/2

OUTPUT

SIGNAL

EOUTx

AVDD

VTRPL

ANALOG

TRIP

Figure 68. Analog Trip Circuit

The analog trip thresholds are programmable with external

resistors and can be calculated using the following equations:

 

V0.01

kΩ

TRP



 



V0.01

kΩ

TRPL

where:

VTRP is the high analog trip threshold voltage.

VTRPL is the low analog trip threshold voltage.

RTRP is the resistance connected between the VTRP pin and

ground.

RTRPL is the resistance connected between the VTRPL pin and

ground.

Note that there are limitations when choosing the RTRP and RTRPL

values to set the analog trip thresholds. The following

requirements must be met.

For RTRP selection,







0.5

100 kΩ

TRP

VREG





and







0.1

100 kΩ

TRP

AVDD





For RTRP selection,

 



kΩ

TRPL

If the analog trip function is not used, connect both VTRP and

VTRPL to VREG to disable the analog trip function.

In the CT current sense application where the input signal is

half-sinusoid, only VTRP, the high analog trip threshold, is

needed. Connect VTRPL to VREG to disable VTRPL, the low analog

trip threshold. Connect RCOM and VCOM to ground in this

CT current sense application.

ACTUATOR DRIVER

The actuator driver receives the input signal either from the

TRG pin or from the output of the analog trip control circuit.

The driver also provides the gate drive voltage for the external

thyristor through the GATE pin, as shown in Figure 69. When

the analog trip protection is triggered, the analog trip control

circuit outputs a 10 ms high, 6 ms low pulse signal. This pulse

signal performs an OR logic with the signal on the TRG pin and

inputs to the actuator driver circuit to provide the gate drive

signal for the external thyristor or MOSFET. During this 16 ms

period, the 10 ms high, 6 ms low pulse signal, any analog trip

signal is ignored. If the analog trip signal is still active after the

16 ms period, another pulse that is 10 ms high, 6 ms low is

generated. If the analog trip signal is cleared after the 16 ms

period, the output of the analog trip control circuit latches to

low. The GATE pin can be pulled up to VREG.

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