TD340

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Reversed battery active protection

In full H-bridge configuration, there is a risk in case of power voltage reversal due to the intrinsic diodes

inside the MOS. A passive protection solution is to wire a diode between the H-bridge and the power

supply. Disadvantages are voltage drop and power dissipation.

The TD340 provides support for reversed battery active protection.

An oscillator OSC output is available to allow proper command of a 5th MOS connected upside down.

The MOS must have low threshold voltage because the oscillator output swing is about 6.5V.

In normal conditions, the MOS intrinsic diode supplies power to the driver at startup. When the TD340 is

started, the OSC output enables the MOS to switch on, providing lower voltage drop and lower power

dissipation.

In case of reversed battery, the 5th MOS remains off, and no dangerous voltages can reach the driver nor

the power MOS.

The OSC oscillator can only supply a few mA. It must be loaded with a large impedance, typically 100pF

and 680k.

Figure 5 : Reversed Battery Active Protection Principle

UVLO and OVLO protections

The TD340 includes protections again overvoltage and undervoltage conditions.

Overvoltage is dangerous for the MOS and for the load due to possible excessive currents and power

dissipation.

Undervoltage is dangerous because MOS driving is no more reliable. MOS could be in linear mode with

high ohmic dissipation.

TD340 Under Voltage LockOut and Over Voltage LockOut features protect the system from no

operational power voltage. UVLO and OVLO thresholds are 6.2V and 20V. Hysteresis provides reliable

behavior near the thresholds.

During UVLO and OVLO, MOS are switched off (TD340 in disable state).

M

TD340

Vbatt

1

2

3

4

2

3

VBATT

GND

REVERSED BATTERY

5

MOSFET 5

REMAINS

OFF

ALL MOSFETS AND DRIVER ARE PROTECTED

Driver is not supplied

Osc

M

TD340

Vbatt

Osc

1

2

3

4

2

3

VBATT

GND

~Vbatt

Normal Conditions

Vbatt+6V