AD7280 datasheet(15/33 Pages) AD

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Preliminary Technical Data

AD7280

Rev. PrD | Page 15 of 33

CNVST

INTERNAL ADC

CONVERSIONS

VOLT 2

VOLT 3

TEMP 6

tCONVERT

VOLT 1

tCONVERT

tACQ

Figure 12. ADC conversions on the AD7280

SCLK

SERIAL READ OPERATION

24 x NO. OF CONVERSIONS

tQUIET

CNVST

INTERNAL ADC

CONVERSIONS

V 1

V 3

V 2

T 6

V 1

V 2

Figure 13. ADC conversions & Readback on the AD7280

Converting Cell Voltages and Temperatures with a chain

of AD7280s

The AD7280 provides a daisy chain interface which allows up to

50 parts to be stacked without the need for individual isolation.

One feature of this daisychain interface is the ability to initiate

conversions on all parts in the daisychain stack with a single

conversion start command. The conversion can be initiated

through a single CNVST pulse or through the rising edge of CS

on the SPI interface. The convert start command is transferred

up the daisychain, from the master device, to each AD7280 in

turn. The delay time between each AD7280 is tDELAY, as outlined

in Figure 14. The maximum delay between the start of

conversions on the master AD7280 and the last AD7280 device

in the chain can be determined by multiplying tDELAY by the

number ofAD7280s in the daisychain. The total conversion

time for all cell voltage and temperature conversions can be

calculated using the following equation:

Total Conversion time = ((tACQ + tCONV) × (#conversions per

part) - tACQ + (#parts x tDELAY)

Where

tACQ is the analog input acquisition time of the AD7280 as

outlined in Table 7

tCONV is the conversion time of the AD7280 as outlined in Table

#conversions per part is 6, 9 or 12 as outlined in Table 6.

#parts is the number of AD7280s in the daisychain

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