BQ76PL455APFCT datasheet(40/125 Pages) TI1

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bq76PL455A

SLUSCL0A – SEPTEMBER 2016 – REVISED OCTOBER 2016

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FAULT_AUX[AUX_UV_FAULT, AUX_OV_FAULT] will be continually set based on the currently stored ADC

result and threshold. This allows testing of the threshold and fault by changing the threshold without having to

sample the channel.

Example:

The design requires AUX0 and AUX1 undervoltage threshold at 1 V and AUX0 and AUX1 overvoltage

threshold at 3 V. The design requires that no FAULT pin activation result from AUX UV or OV conditions on

AUX2…AUX7. Set the following conditions:

AUX0_UV = 1 V, AUX0_OV = 3 V

AUX1_UV = 1 V, AUX1_OV = 3 V

AUX2_UV = 0 V, AUX2_OV = 5 V

AUX3_UV = 0 V, AUX3_OV = 5 V

AUX4_UV = 0 V, AUX4_OV = 5 V

AUX5_UV = 0 V, AUX5_OV = 5 V

AUX6_UV = 0 V, AUX6_OV = 5 V

AUX7_UV = 0 V, AUX7_OV = 5 V

7.3.12.8 Secondary Protectors: Analog Window Comparators for Cell UV/OV

Thirty-two analog comparators, connected in pairs as window comparators for the 16 channels, provide cell-

voltage monitoring that is separate from the main acquisition path and work in parallel with the main ADC route.

Configuration of the faults sensed by the analog window comparators is by the number of channels enabled in

the NCHAN register. In case of malfunction of the AFE or ADC, the analog comparators will still be able to flag

the crossing of the (register selectable) undervoltage and overvoltage comparator thresholds.

To avoid undesired comparator faults, two internal DACs set the separate overvoltage (COMP_OV) and

undervoltage (COMP_UV) thresholds. The DACs use the REF2 (4.5 V) reference, which is a separate circuit

from the 2.5 V (VREF) ADC reference. The OV threshold can range from 2 V to 5.175 V in steps of 25 mV. The

UV threshold can range from 0.7 V to 3.875 V in steps of 25 mV.

NOTE

When the cell voltage is very close to the comparator thresholds, enabling or disabling cell

balancing may result in transient comparator faults.

Use the DEVCONFIG[COMP_CONFIG] register to enable OV and UV faults, OV-only faults, or no faults.

Enabling UV-only faults is not possible.

NOTE

If the comparators are disabled then re-enabled during normal operation (such as after

startup has occurred), the OV faults are signaled and must be manually cleared.

7.3.12.8.1

Window Comparator Special Considerations

As shown in Figure 24, there are resistors of approximately 100

Ω in series with each VSENSE pin that isolate

the connections to the AFE from the secondary-protector circuits (window comparators). This isolator allows

detection of common-cause failures affecting both the AFE and secondary-protector circuits.

A Squeeze function in the device helps to detect open-sense wire (to the monitored cell) conditions. When the

Squeeze function turns on, it places an approximately 5-kΩ resistance across adjacent VSENSE inputs, and

creates an additional voltage drop through the approximately 100-

Ω series resistors. This causes the apparent

increase in the voltage applied to the window-comparator blocks immediately above, and below, the inputs that

have the Squeeze resistor applied. Only the comparators can see the increased voltage not the AFE. This in turn

may cause the OV comparator fault to trip, even if the external sense-pin voltage measurement says otherwise,

depending on the OV threshold.

BQ76PL455APFCT Datasheet(PDF) 40 Page - Texas Instruments

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