LTC2420CS8 datasheet(29/36 Pages) LINER

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LTC2420

SYNCHRONIZATION OF MULTIPLE LTC2420s

Since the LTC2420’s absolute accuracy (total unadjusted

error) is 10ppm, applications utilizing multiple matched

ADCs are possible.

Simultaneous Sampling with Two LTC2420s

One such application is synchronizing multiple LTC2420s,

see Figure 35. The start of conversion is synchronized to

the rising edge of CS. In order to synchronize multiple

LTC2420s, CS is a common input to all the ADCs.

To prevent the converters from autostarting a new con-

version at the end of data output read, 23 or fewer SCK

clock signals are applied to the LTC2420 instead of 24 (the

24th falling edge would start a conversion). The exact

timing and frequency for the SCK signal is not critical

since it is only shifting out the data. In this case, two

LTC2420’s simultaneously start and end their conversion

cycles under the external control of CS.

TYPICAL APPLICATIO S

Increasing the Output Rate Using Multiple LTC2420s

A second application uses multiple LTC2420s to increase

the effective output rate by 4

×, see Figure 36. In this case,

four LTC2420s are interleaved under the control of sepa-

rate CS signals. This increases the effective output rate

from 7.5Hz to 30Hz (up to a maximum of 400Hz). Addi-

tionally, the one-shot output spectrum is unfolded allow-

ing further digital signal processing of the conversion

results. SCK and SDO may be common to all four LTC2420s.

The four CS rising edges equally divide one LTC2420

conversion cycle (7.5Hz for 60Hz notch frequency). In

order to synchronize the start of conversion to CS, 23 or

less SCK clock pulses must be applied to each ADC.

Both the synchronous and 4

× output rate applications use

the external serial clock and single cycle operation with

reduced data output length (see Serial Interface Timing

Modes section and Figure 7). An external oscillator clock

is applied commonly to the FO pin of each LTC2420 in

order to synchronize the sampling times. Both circuits

may be extended to include more LTC2420s.

23 OR LESS CLOCK CYCLES

SCK1

SCK2

2420 F35

SDO1

SDO2

23 OR LESS CLOCK CYCLES

LTC2420

VCC

VREF

VIN

GND

SCK

SDO

SCK2

SCK1

SDO1

SDO2

LTC2420

VCC

VREF

VIN

GND

SCK

SDO

µCONTROLLER

EXTERNAL OSCILLATOR

(153,600HZ)

VREF

(0.1V TO VCC)

Figure 35. Synchronous Conversion—Extendable

LTC2420CS8 Datasheet(PDF) 29 Page - Linear Technology

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