ADBMS2950BCCSZ datasheet(93/97 Pages) AD

93 / 97 page

Data Sheet

ADBMS2950B

Rev. 0 | Page 93 of 97

maximum (MAX) oscillator frequency. Every time CntACC

increments by one, a new IxACC result appears, assuming the

host implements the following read sequence:

•

SNAP (to freeze all the result registers)

•

RDFLAG (to get I1CNT, I1PHA)

•

RDIACC (to get the accumulated conversion results)

•

… (any other readings, for example, VBxACC results)

•

UNSNAP (to un-freeze all result registers)

This sequence is equivalent to:

•

UNSNAP (to un-freeze all result registers)

•

SNAP (to freeze all the result registers)

•

RDFLAG (to get I1CNT, I1PHA)

•

RDIACC (to get the accumulated conversion results)

•

… (any other readings without final unsnap)

The advantage of the second sequence is that there is an

intrinsic check that all commands are executed correctly

without relying on the following read command that checks the

command counter increment after the final unsnap of the first

sequence. The initial commands unsnap, snap used here ensure

a new snapshot of the result registers is taken before executing

the read commands. When implementing this approach, the

unsnap, snap commands must precede any other sequences that

read results marked with the FRZ identify in the register and bit

description tables. This ensures coherent data reading, for

details, see the Snapshot Commands section.

In both the sequences, the snapshot commands ensure that

I1CNT, I1PHA, and conversion results are read coherently

allowing the host to decide for every dataset if a new result is

read (CntACC incremented by one in Table 89) or if the dataset

is old and can be discarded. For example, Table 89 shows the

column CntACC-MIN did not increment between #4 and #5

remaining at 3 conversions. Still, a hypothetical device running

at the nominal oscillator frequency has already provided the 4th

sample as shown in column CntACC-NOM.

Table 89 also shows the I1CNT rolling over to 0 after the

maximum value, which is 211 − 1 = 2047. The host controller

must take this into account when evaluating I1CNT. A simple

way is to check if I1CNT is bigger or equal than N × 8, where N

initially starts at 1, is incremented by 1 every time the check is

true (new conversion) and is reset to 0 every time the current

read I1CNT value is smaller than the previous one.

After starting continuous measurement, set initial values:

INIT

N = 1

I1CNT_OLD = 0

ENDINIT

In the measurement loop, evaluate the dataset read through the

above-described sequence (ReadSequence) and do the

following:

LOOP

ReadSequence()

IF I1CNT < I1CNT_OLD

N = 0

ENDIF

IF I1CNT ≥ N × 8

N = N + 1

// process new conversions read from IxACC

(and VBxACC)

ELSE

// Old conversion was already read

// nothing to do

I1CNT_OLD = I1CNT

ENDIF

ENDLOOP

Note that this example assumes ACCN = 8 and must be

adjusted for different settings of ACCI.

Table 89 assumes that the host activates the continuous current

measurement (on I1ADC or I1ADC and I2ADC) through

ADI1 command at the time t = 0s. The first reading happens

directly afterwards and subsequently every 7 ms. # is the index

of the read sequence.

Table 89. I1CNT and IxACC Update Timing for Minimum, Nominal and Maximum Oscillator Frequency Assuming ACCN = 8

t [s]

I1CNT-MIN

I1CNT-NOM

I1CNT-MAX

CntACC-MIN

CntACC-NOM

CntACC-MAX

0.007

0.014

0.021

0.028

0.035

0.042

...

0.238

213

237

261

0.245

220

244

268

0.252

226

251

276

0.259

232

258

284

0.266

238

265

292

...

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