DRV401-Q1 Datasheet, PDF (22/39 Pages) Texas Instruments – DRV401-Q1 Sensor Signal Conditioning Device for Closed-Loop Magnetic Current Sensor

DRV401-Q1
SBOS814 – DECEMBER 2016
www.ti.com
7.3.9 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, as shown in Figure 46 through Figure 49. During this time the ERROR flag remains low,
indicating the not ready condition. Maintaining DEMAG low prevents this cycle, and the DRV401-Q1 device 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) must not differ by more than 100 mV for proper device operation. They are
normally connected together or separately filtered as shown in Layout.
The DRV401-Q1 device tests for low supply voltage with a brownout voltage level of 4 V; proper power
conditions must be supplied. Good power-supply and low equivalent series resistance (ESR) bypass capacitors
are required to maintain the supply voltage during the large current pulses that the DRV401-Q1 device drives.
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 Probe Coil Loop, Internal Resistor parameters in the Electrical Characteristics table) sets the
lower limit for the acceptable supply voltage. Voltage drops lasting less than 31 μs are ignored. The probe error
detection activates the ERROR pin when proper oscillation fails for more than 32 μs.
A low supply voltage condition, or brownout, 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)
initiates a power-on reset.
7.3.10 Error Conditions
In addition to the overrange flag that indicates signal clipping in the output amplifier (differential amplifier), a
system error flag is provided. The ERROR flag indicates conditions when the output voltage does not represent
the primary current. The ERROR flag is active during a demagnetization cycle, power-fail, or brownout. The
ERROR flag becomes active with an open or short-circuit in the probe loop. When the error condition is no longer
present and the circuit returns to normal operation, the flag resets.
The ERROR and overrange flags are open-drain logic outputs. The flags connect together for a wired-OR and
require an external pull-up resistor for proper operation.
The following conditions result in ERROR flag activation (ERROR asserts low):
1. The probe comparator stays low for more than 32 μs. This condition occurs if the probe coil connection is
open or if the supply voltage dips to the level where the required saturation current cannot be reached.
During the 32-μs timeout, the I_COMP driver remains active but goes inactive thereafter. In case of recovery,
ERROR is low and the I_COMP driver remains in reset for another 3.3 ms.
2. The probe driver pulse-width is less than 280 ns for three consecutive periods. This condition indicates a
shorted field probe coil or a fully-saturated sensor at start-up. If this condition persists longer than 25 μs and
then recovers, the ERROR flag remains low and I_COMP is in reset for another 3.3 ms. If the condition lasts
less than 25 μs, the ERROR flag recovers immediately and the I_COMP driver is not interrupted.
3. During demagnetization, if the cycle is aborted early by pulling DEMAG low, the ERROR flag stays low for
another 3.3 ms (I_COMP is disabled during this time).
4. An open compensation coil is detected (longer than 100 μs). This condition indicates that not enough current
is flowing in the I_COMP driver output; this condition may be the result of a high-resistance compensation coil or
the connection of an external driver. Detection of this condition can be disabled by setting the CCdiag pin
low.
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