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ATA6821

4778A–AUTO–11/03

Functional Description

The ATA6821 controls a push-pull power output stage for an external power device and

a feedback output stage. If the voltage at the input pin is > 7 V, both outputs are at

“high-level”, if the input voltage falls below the switch-off threshold of 4 V, both outputs

are switched to ground.

If a rectangular input signal is fed to the input, the feedback ouput “Feed” is not used

and pin 8 needs no external connection.

In case the input signal, however, comes from a transformer (potential-free control; see

Figure 7 on page 11), the integrated pulse shaping circuit is used to achieve a reliable

feedback configuration at the input. This ensures correct switching of the output stage

even if the input signal is very noisy.

For the timing of input and output signals and the slew rates, please refer to Figure 3 on

page 8. The timing diagram is based on the following test conditions: A 2 k

W resistor is

connected between pin 8 and ground; a 2 k

W resistor and a 1 nF capacitor are used as

load for the power output (pins 13 and 14) simulating identical conditions as a power

MOSFET, which is usually connected to the output.

Undervoltage Detection

During power-up and power-down of the supply voltage, the internal undervoltage circuit

suppresses uncontrolled output pulses. In case of undervoltage (V

back output and the power output are switched off and locked for 40 ms.

When the supply voltage has reached the switch-on-threshold of about 17 V, both out-

put stages are enabled after a delay time of 40 ms.

Voltage Monitoring

An effective short-circuit detection of the external device is achieved by a drain-source

voltage monitor.

The voltage monitor comparator (pin 3) has a threshold of 1/3

´ V

applied to pin 3 exceeds this voltage, both output stages are switched off immediately

and locked for 20 ms. With a hysteresis of 200 mV, the outputs are enabled again after

a delay time of 20 ms. A voltage divider connected to V

age to pin 3. A decoupling diode is recommended if the external power device‘s drain

source voltage exceeds 30 V (see Figure 5 on page 9).

With the help of an external capacitor, connected to pin 3, the switching characteristic of

the voltage monitor comparator can be varied according to the rising edge of the input

signal at pin 9. During the off cycle, the capacitor is discharged, during the on-cycle, it is

charged again.

If the voltage monitoring function is not used, pin 3 should be connected to ground (see

Figure 4 on page 9).

Application Hints

Due to high peak output currents, the layout of the PC board is essential. Appropriate

decoupling capacitors should be used, otherwise, the performance of the driver

degrades severely. It is strongly recommended to connect the blocking capacitors (low

ESR types) as close as possible to the power supply and the ground pins. If necessary,

two or more capacitors of different types may be connected in parallel.

The two power ground pins, the ground pin, the two output pins and the two supply pins

should be externally connected together as close as possible to the pins.

The measurement pin (pin 5) and the test pin (pin 7) must not be used in any application

and need to be tied to ground.