SIM6800M datasheet(25/52 Pages) SANKEN

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SIM6800M Series

SIM6800M-DSE Rev.1.5

SANKEN ELECTRIC CO., LTD

Jul. 18, 2018

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

12.3.5

Overcurrent Protection (OCP)

The overcurrent protection (OCP) is a protection

against large inrush currents (i.e., high di/dt). Figure

12-14 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 currents running

through the shunt resistors, RSx.

Figure 12-15 is a timing chart that represents

operation waveforms during OCP operation. When the

OCP pin voltage increases to the OCP Threshold

Voltage (VTRIP, 1.0 V) or more, and remains in this

condition for a period of the OCP Blanking Time (tBK, 2

μs) or longer, the OCP circuit is activated. The enabled

OCP circuit shuts off the low-side transistors and puts

the FO pin into a low state. Then, output current

decreases as a result of the output transistors turn-off.

Even if the OCP pin voltage falls below VTRIP, the IC

holds the FO pin in the low state for a fixed OCP hold

time (tP) of 25

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.

For proper shunt resistor setting, your application

must meet the following:

● Use the shunt resistor that has a recommended

resistance, RSx (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 1).

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.

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

and CO. The larger the time constant, the longer the time

that the OCP pin voltage rises to VTRIP. And this may

cause

permanent

damage

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 time constants must be

set to the values listed in Table 12-3. And place CO as

close as possible to the IC with minimizing a trace

length between the OCP and COMx pins.

Note that overcurrents are undetectable when one or

more of the U, V/V1/V2, and W1/W2 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

COM2

A/D

RSx

ROx

DRSx

VTRIP

200 k

Blanking

filter

Output SW turn-off

and QFO turn-on

1.65 µs (typ.)

2 k

Figure 12-14.

Internal Circuit Diagram of OCP Pin

and Its Peripheral Circuit

LINx

HINx

HOx

LOx

OCP

VTRIP

tBK

VLIM

HOx responds to input signal.

FO restarts

automatically after tP.

Figure 12-15.

OCP Operational Waveforms

Table 12-3.

Reference Time Constants for CR Filter

Part Number

Time Constant

(µs)

SIM681x

≤2

SIM682x

SIM688x

≤0.2

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