ADBMS2950BCCSZ datasheet(32/97 Pages) AD

32 / 97 page

ADBMS2950B

Data Sheet

Rev. 0 | Page 32 of 97

The IxCAL bits are low until the initialization process has

completed, after 136 conversions. The total time required for

initialization = tIxADC_STARTUP + tIxADC_INIT.

When initialization is started by an ADV or ADX command, no

IxADC results are available, and IxCNT remains zero. For this

reason, it is recommended to start the initialization through a

continuous ADIx command and wait for 136 conversion cycles

(when IxCNT reports 136 the first time) before reading the

IxADC results for the first time.

From power-up or SRST, it takes tWAKE + tREFUP + tIxADC_STARTUP +

tIxADC_INIT for the IxADCs to meet the accuracy specification.

The VBxADC results are available during the initialization

process. All other ADCs are unaffected by the initialization

process.

IxADC Open-Wire Current Sources

As shown in Figure 1, the ADBMS2950B features current

sources at the inputs of both current measurement channels.

Activating these current sources allows the detection of a

broken connection to a shunt resistor. The Open-wire current

sources are configured by the DIAGSEL configuration register

and activated by issuing a diagnostic ADI1 or ADI2

measurement through the OPT command bits. The current

sources have a value of about 0.5 μA. As the open-wire current

sources are connected after a 3.8 kΩ ESD protection resistor,

activating them changes the reading of the corresponding

IxADC by about 1.9 mV, while it does not affect the reading of

the other IxADC. It also does not affect any of the OCxADC

readings.

Redundant I2ADC and VB2ADC diagnostic measurements

(synchronous to I1ADC and VB1ADC for redundancy) must

be terminated through one of the two ADI2 single-shot

measurement (non-diagnostic) or any other ADI2 single-shot

diagnostic (DIAGSEL) measurement command after DIAGSEL

has been set to 0b000.

Battery Voltage Measurements

The ADBMS2950B features two dedicated battery-stack voltage

measurement paths that connect to one or two external resistor-

dividers through the VBAT1 and VBAT2 pins. The voltage at

these pins is first buffered to provide a high input resistance and

then applied to two 16-bit ADCs. VB1ADC operates

simultaneously and synchronously to I1ADC whenever an

ADI1 command is issued. Diagnostic measurements selected

through DIAGSEL and activated through OPT command bits

are also performed on both ADCs simultaneously. The same is

valid for VB2ADC, which operates simultaneously and

synchronously to I2ADC. If ADI1 is issued with the RD

command bit set, all four ADCs operate synchronously,

irrespective of whether the OPT bits are set to single-shot or

continuous mode.

Redundant I2ADC and VB2ADC diagnostic measurements

(synchronous to I1ADC and VB1ADC for redundancy) must

be terminated through one of the two ADI2 single-shot

measurement (non-diagnostic) or any other ADI2 single-shot

diagnostic (DIAGSEL) measurement command after DIAGSEL

has been set to 0b000.

VBxADC Open-Wire Current Sources

Similar to the IxADCs, the VBxADCs feature current sources

connected to their inputs. The open-wire current source has a

value of 10 μA and is preceded by a 2.3 kΩ ESD protection

resistor, leading to a typical change in ADC output of about

23 mV.

Continuous or Single-Shot Measurements

The IxADC and VBxADC can be configured to perform a

single measurement or continuous measurements, which are

controlled by the OPT command bits. In continuous mode, the

result registers of the corresponding ADCs are updated at their

conversion rate (nominally 1 ms for the Ix, VBx registers, and

1 ms times ACCN for the accumulated result registers IxACC,

VBxACC) for non-diagnostic measurements.

For diagnostic measurements, the content of the accumulated

IxADC result registers is not valid and must be ignored and

only the 1 ms conversion results must be used. The

accumulated VBxADC result registers can be used for

diagnostic and non-diagnostic measurements. To end the

continuous measurement mode of the respective ADCs, a

single-shot ADI1 or ADI2 command must be sent. The

addressed ADCs then perform the last single-shot

measurement and stop.

Conversion Results Accumulation

In the continuous diagnostic measurement mode, the VBxADC

conversions are summed up to the accumulation results

VBxACC. The current measurement accumulation results

IxACC are not valid during diagnostic operation. In continuous

non-diagnostic measurement mode, the IxADC and VBxADC

results are summed up to the accumulation results IxACC and

VBxACC.

The ACCI (and the resulting ACCN) register configures the

number of IxADC and VBxADC conversions (ACCN) that are

accumulated internally before being stored to the IxACC and

VBxACC registers. The ACCI configuration becomes active

only with the next ADI1 or ADI2 command. The internal

accumulators are cleared to start a new cycle after the

accumulation result registers have been updated. The update

rate of those registers thus depends on ACCN, which can be set

to be slower than the host controller update rate, allowing to

read back-to-back conversion results.

The conversion counters I1CNT and I2CNT allow to identify

new conversions and discard those that are already read.

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