MAX11150 datasheet(21/26 Pages) MAXIM

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Daisy-Chain Mode, No-Busy Indicator

The daisy-chain mode with no-busy indicator is ideally suit-

ed for multichannel isolated applications that require mini-

mal wiring complexity. Simultaneous sampling of multiple

ADC channels is realized on a 3-wire serial interface where

data readback is analogous to clocking a shift register. In

Figure 13, two ADCs are connected to an SPI-compatible

digital host with corresponding timing given in Figure 14.

The daisy-chain mode is engaged when the MAX11150

detects the low state on SDI at the rising edge of CNVST.

In this mode, CNVST is brought low and then high to trigger

the completion of the acquisition phase and the start of a

conversion. A low SCLK state on the rising edge of CNVST

signals to the internal controller that the no-busy indicator

will be output. When in chain mode, the SDO output is

driven active at all times.

When SDI and CNVST are both low, SDO is driven low,

thus engaging the daisy-chain mode of operations on the

downstream MAX11150 parts. For example, in Figure 13

part A has its SDI tied low so the chain mode of operation

will be selected on every conversion. When CNVST goes

low to trigger another conversion, part A’s SDO and con-

sequently part B’s SDI go low as well. On the next CNVST

rising edge both parts A and B will select the daisy-chain

mode interface.

When a conversion is complete, the MSB is presented onto

SDO, and the MAX11150 returns to the acquisition phase.

The remaining data bits, stored within the internal shift

edge. The SDI input of each ADC in the chain is used to

transfer conversion data from the previous ADC into the

internal shift register of the next ADC, thus allowing for data

to be clocked through the multichip chain on each SCLK

falling edge. Each ADC in the chain outputs its MSB data

first requiring 18 × N clocks to read back N ADCs.

In daisy-chain mode, the maximum conversion rate is

reduced due to the increased readback time. For instance,

with a 6ns digital host setup time and 3V interface, up to

four MAX11150 devices running at a conversion rate of

310ksps can be daisy-chained on a 3-wire port.

Figure 13. Daisy-Chain Mode, No-Busy Indicator Connection Diagram

Figure 14. Daisy-Chain Mode, No-Busy Indicator Serial Interface Timing

SDO

SDI

SCLK

CLK

DATA IN

DIGITAL HOST

CNVST

CONVERT

SDO

SDI

SCLK

CNVST

MAX11150

Device A

Device B

SDOA

SDOB

DA17

SCLK

SDOA = SDIB

CNVST

tCONV

CONVERSION

ACQUISITION

tACQ

DA16

DA15

DA1

DA0

tSCLK

tSCLKL

tSCLKH

tDSDO

tHSCKCNV

tSSCKCNV

SDOB

DB17

DB16

DB15

DB1

DB0

DA17

DA16

DA1

DA0

tSSDISCK

tHSDISCK

tCNVPW

tCYC

SELECT NO

BUSY

OUTPUT

SELECT CHAIN

MODE

MAX11150

18-Bit, 500ksps, +5V SAR ADC with

Internal Reference in µMAX

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