SCM3000C datasheet(23/41 Pages) SANKEN

23 / 41 page

SCM3000C Series

SCM3000C-DSE Rev.1.2

SANKEN ELECTRIC CO., LTD.

Aug. 21, 2017

http://www.sanken-ele.co.jp/en

12.3.3. Overcurrent Protection (OCP)

Figure 12-18 is an internal circuit diagram describing

the OCP pin and its peripheral circuit. The OCP pin

detects overcurrents with the input voltages across

external shunt resistors, RSx. Because the OCP pin is

internally pulled down, the OCP pin voltage increases

proportionally to a rise in the current running through

the shunt resistor, RSx.

Figure 12-19 is a timing chart that represents

operation waveforms during OCP operation. When the

OCP pin voltage increases to the Overcurrent Protection

Threshold Voltage (VTRIP, 0.500 V) or more, and

remains in this condition for a period of the Overcurrent

Protection Blanking Time (tBK, 0.5

μs) or longer, the

OCP is activated. The enabled OCP circuit then shuts off

the output transistors and puts the FO pin into a logic

low state. And output current decreases after the output

transistors turn off. Even if the OCP pin voltage falls

below VTRIP, the IC holds the FO pin the logic low state

for a fixed OCP hold time (tP) of 30

μs (typ.). Then, the

output transistors operate according to input signals.

The OCP is used for detecting abnormal conditions,

such as an output transistor shorted. In case short-circuit

conditions occur repeatedly, the output transistors can be

destroyed. To prevent such event, motor operation must

be controlled by the external microcontroller so that it

can immediately stop the motor when fault signals are

detected. When putting the IC back to normal operation,

you must set up a wait time of 2 seconds or longer

before resuming the IC operation.

For proper shunt resistor setting, your application

must meet the following:

● Use the shunt resistor a recommended resistance, R

(see Section 2).

● Set the OCP pin input voltage to vary within the rated

OCP pin voltages, VOCP (see Section 1).

● Keep the current through the output transistors below

the rated output current (pulse), IOP (see Section 2).

It is required to use a resistor with low internal

inductance because high-frequency switching current

will flow through the shunt resistors, RSx. In addition,

choose a resistor with allowable power dissipation

according to your application.

As illustrated in Figure 12-18, a 4.7 nF chip capacitor,

COIN, is internally connected to the OCP pin. When you

connect a CR filter (i.e., a pair of a filter resistor, RO,

and a filter capacitor, CO) to the OCP pin, care should be

taken in setting the time constants of RO, CO, and COIN.

The larger the time constant, the longer the time that the

OCP pin voltage rises to VTRIP. And this may cause

permanent damage to the transistors. Consequently, a

propagation delay of the IC must be taken into account

when you determine the time constants. For RO and CO,

their values should satisfy Equation (3):

RO×(CO+4.7nF)<1.0µs.

(3)

It is recommended to use RO with a resistance up to

200 Ω and C

O with a capacitance of about 4.7 nF. And

place CO as close as possible to the IC with minimizing a

trace length between the OCP and COM pins.

Note that overcurrents are undetectable when one or

more of the U, V, and W pins or their traces are shorted

to ground (ground fault). In case any of these pins falls

into a state of ground fault, the output transistors may be

destroyed.

VBB

LSx

COM

OCP

COM

A/D

DRS

VTRIP

100k

Blanking

filter

Output SW turn-off

and QFO turn-on

0.5µs(typ.)

COIN

Figure 12-18.

Internal Circuit Diagram of OCP Pin

and Its Peripheral Circuit

LINx

HINx

HOx

LOx

OCP

VTRIP

tBK

tDELAY 0.3 µs (typ.)

tBK

FO restarts

automatically after tP.

HOx responds to input signal.

Figure 12-19.

OCP Operational Waveforms

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