POWER-ON AND BROWNOUT

DRV401-EP

cycle is started (see Figure 7a). During this time the ERROR flag remains low, indicating the not ready condition.

Maintaining DEMAG low prevents this cycle, and the DRV401 starts operation approximately 32

µs after

power-up. If no probe error conditions are detected within four full cycles (that is, the probe half-periods are

shorter than 32

µs and longer than 280 ns), the compensation driver starts and the ERROR pin indicates the

ready condition by going high, typically about 42

µs after power-up.

NOTE:

An external pull-up resistor is required to pull the ERROR pin high.

normally connected together or separately filtered (see Layout Considerations).

The DRV401 tests for low supply voltage with a brown-out voltage level of +4 V; proper power conditions must

be supplied. Good power-supply and low ESR bypass capacitors are required to maintain the supply voltage

during the large current pulses that the DRV401 can drive.

A critical voltage level is derived from the proper operation of the probe driver. The probe interface relies on a

peak current flowing through the probe to trip the comparator. The probe resistance plus the internal resistance

of the driver (see Electrical Characteristics specification, Probe Coil Loop, Internal Resistor) sets the lower limit

for the acceptable supply voltage. Voltage drops lasting less than 31 ms are ignored. The probe error detection

activates the ERROR pin as soon as proper oscillation fails for more than 32

µs.

A low supply voltage condition, or brown-out, is detected at +4 V. Short and light voltage drops of less than

100

µs are ignored, provided the probe circuit continues to operate. If the probe no longer operates, the ERROR

pin goes active. Signal overload recovery is only provided if the probe loop was not discontinued.

A supply drop lasting longer than 100

µs generates power-on reset. A voltage dip down to +1.8 V (for V

initiates a power-on reset.

Copyright © 2008, Texas Instruments Incorporated

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Product Folder Link(s): DRV401-EP