DRV401-EP_09 Datasheet, PDF (21/33 Pages) Texas Instruments – SENSOR SIGNAL CONDITIONING IC FOR SENSOR SIGNAL CONDITIONING IC FOR

DRV401-EP
www.ti.com .................................................................................................................................................. SBVS104B – JANUARY 2008 – REVISED MARCH 2009
POWER-ON AND BROWNOUT
Power-on is detected with the supply voltage going higher than 4 V at V_DD1. When DEMAG is high, a degauss
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.
Both supply pins (V_DD1 and V_DD2) should not differ by more than 100 mV for proper device operation. They are
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_DD1) also
initiates a power-on reset.
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