Data Sheet

15

Rev. 1.0, 2009-03-31

High Current PN Half Bridge

BTN7975B

Block Description and Characteristics

5.3

Protection Functions

The device provides integrated protection functions. These are designed to prevent IC destruction under fault

conditions described in the data sheet. Fault conditions are considered as “outside” normal operating range.

Protection functions are not to be used for continuous or repetitive operation, with the exception of the current

limitation (Chapter 5.3.4). In a fault condition the BTN7975B will apply the highest slew rate possible independent

of the connected slew rate resistor. Overvoltage, overtemperature and overcurrent are indicated by a fault current

I

In the following the protection functions are listed in order of their priority. Overvoltage lock out overrides all other

error modes.

5.3.1

Overvoltage Lock Out

To assure a high immunity against overvoltages (e.g. load dump conditions) the device shuts the lowside MOSFET

off and turns the highside MOSFET on, if the supply voltage is exceeding the over voltage protection level

V

The IC operates in normal mode again with a hysteresis

V

on voltage

V

during over voltage.

5.3.2

Undervoltage Shut Down

To avoid uncontrolled motion of the driven motor at low voltages the device shuts off (output is tri-state), if the

supply voltage drops below the switch-off voltage

V

if the supply voltage rises above the switch-on voltage

V

5.3.3

Overtemperature Protection

The BTN7975B is protected against overtemperature by an integrated temperature sensor. Overtemperature

leads to a shut down of both output stages. This state is latched until the device is reset by a low signal with a

minimum length of

t

Repetitive use of the overtemperature protection impacts lifetime.

5.3.4

Current Limitation

The current in the bridge is measured in both switches. As soon as the current in forward direction in one switch

(high side or low side) is reaching the limit

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During that time all changes at the IN pin are ignored. However, the INH pin can still be used to switch both

MOSFETs off. After

t

2*

t

the motor) is suppressed by internal filter circuitry. Due to thresholds and reaction delay times of the filter circuitry

the effective current limitation level

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