SC225KSIT datasheet(11/13 Pages) SECELECTRONICS

11 / 13 page

SC225KSIT

120 kHz Bandwidth, High Voltage Isolation

Current Sensor with Integrated Overcurrent Detection

11/13

Setting Overcurrent Fault Switchpoint

The VOC needed for setting the overcurrent fault switchpoint can be calculated as follows:

VOC = Sens × | IOC | ,

where VOC is in mV, Sens in mV/A, and IOC (overcurrent fault switchpoint) in A.

| Ioc | is the overcurrent fault switchpoint for a bidirectional (AC) current, which means a

bi-directional sensor will have two symmetrical overcurrent fault switchpoints, +IOC and –IOC .

See the following graph for IOC and VOC ranges:

Example:For SC225KSIT, if required overcurrent fault switchpoint is 50 A, and VCC = 5 V, then the

required VOC can be calculated as follows:

VOC = Sens × IOC = 28 × 50 = 1400 (mV)

Overcurrent Fault Operation

The primary concern with high-speed fault detection is that noise may cause false tripping. Various

applications have or need to be able to ignore certain faults that are due to switching noise or other

parasitic phenomena, which are application dependant. The problem with simply trying to filter out

this noise in the main signal path is that in high-speed applications, with asymmetric noise, the act of

filtering introduces an error into the measurement.

To get around this issue, and allow the user to prevent the fault signal from being latched by noise, a

circuit was designed to slew the FAULT pin voltage based on the value of the capacitor from that pin

to ground. Once the voltage on the pin falls below 2 V, as established by an internal reference, the

fault output is latched and pulled to ground quickly with an internal N-channel MOSFET.

Fault Walk-through

The following walk-through references various sections and attributes in the figure below. This figure

shows different fault set/reset scenarios and how they relate to the voltages on the FAULT pin,

FAULT_EN pin, and the internal Overcurrent (OC) Fault node, which is invisible to the customer.

Because the device is enabled (FAULT_EN is high for a minimum period of time, the Fault

Enable Delay, tFED , 15 μs typical) and there is an OC fault condition, the device FAULTpin

starts discharging.

SC225KSIT 数据表(PDF) 11 Page - SEC Electronics Inc.