ADBMS2950BCCSZ datasheet(84/97 Pages) AD

84 / 97 page

ADBMS2950B

Data Sheet

Rev. 0 | Page 84 of 97

conversion) that can be introduced by system noise or AC loads

on the VREF1P25 pin scale with the inverse ratio of the divider

to a high-voltage measurement error.

Instead, when the voltage is measured differentially across the

low-side resistor Rlow (Vx vs. VREF1P25 or VBAT1 vs. VBAT2,

where VBAT2 is connected to VREF1P25, see Figure 69), the

measurement error of VREF1P25 translates only 1:1 to high-

voltage measurement error.

Figure 70. VBATx Configuration for Bipolar Single-Ended Redundant

Measurement. Note Limitations in Noisy Environments

DIGITAL FILTERING

Table 88 summarizes the options of digital filtering with the

ADBMS2950B. All are finite impulse response filters (FIR). The

&minu;3 dB corner frequencies are given for the digital filter

outputs without (fc,dig) and with (fc,ana) the preceding analog RC

Filters, which are added with typical values to the filter response

figures shown in this chapter. In most cases, both values are

identical because of the digital filter being dominant.

In Table 88, the column Continuous shows whether the ADC

can convert continuously providing back-to-back conversion

results without measurement holes. The IxADCs and

VBxADCs are recommended to operate in this mode, also see

the chapter Continuous Sampling and Coulomb Counting. The

VxADCs and AUX ADC convert on demand only. New

conversions can be triggered after all requested channels are

converted (see Table 58). Previous conversion results can be

read while a new conversion is ongoing, which allows the

implementation of high update rates if required.

Table 88. Overview of Digital FIR filters of ADBMS2950B

ADC

Filter Output Rate

Filter Function

fc,dig

fc,ana

Continuous

OCxADC

16 kHz

1st order Sinc

7.2 kHz

4.5 kHz

Yes

VxADC, AUX ADC

3.8 kHz

1st order Sinc

1.7 kHz

0.11 kHz

Single-shot through ADV, ADX

IxADC, VBxADC

1 kHz

1st order Sinc

0.44 kHz

Yes

IxADC, VBxADC

250 Hz

Sum of 4 samples (ACCI = 0)

111 Hz

Yes

IxADC, VBxADC

125 Hz

Sum of 8 samples (ACCI = 1)

55 Hz

Yes

IxADC, VBxADC

83.3 Hz

Sum of 12 samples (ACCI = 2)

37 Hz

Yes

IxADC, VBxADC

62.5 Hz

Sum of 16 samples (ACCI = 3)

28 Hz

Yes

IxADC, VBxADC

50 Hz

Sum of 20 samples (ACCI = 4)

22 Hz

Yes

IxADC, VBxADC

41.7 Hz

Sum of 24 samples (ACCI = 5)

18 Hz

Yes

IxADC, VBxADC

35.7 Hz

Sum of 28 samples (ACCI = 6)

16 Hz

Yes

IxADC, VBxADC

31.2 Hz

Sum of 32 samples (ACCI = 7)

14 Hz

Yes

Only the preamplifiers of the IxADC signal path have a low-

pass characteristic, which is shown as PA in Figure 72 and

Figure 73. Other buffers and preamplifiers have a flat filter

response in the frequency range of interest and are not shown

for this reason. The transfer functions are shown for all

preceding filter blocks connected in series as they appear in the

signal data path. RC is the external analog RC-Filter only, PA

(pre-amplifier) is the PA in series with the external RC and 1 ms

is the external RC in series with the PA in series with the ADC

at an update rate of 1 kHz. In the legend text, the 3 dB corner

frequency is shown inside brackets.

OCxADC Filter Transfer Function

Figure 71 shows the transfer function of the OCxADC signal

path with and without the typical external current sense RC

filter at a continuous conversion rate of 16 kHz.

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