ADPD4200 datasheet(14/93 Pages) AD

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Data Sheet

ADPD4200

THEORY OF OPERATION

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Rev. 0 | 14 of 93

Analog Input Multiplexer

The ADPD4200 supports four analog input pins. Each input can be

used as a single-ended input or as part of a differential pair.

Figure 15 shows a single representation of the input switch matrix,

which allows programmable connection to the two AFE channels.

Each pair of inputs has an exact duplicate of this multiplexer: IN1

and IN2, and IN7 and IN8. The connections are programmable per

time slot.

The PAIR12 and PAIR78 bits select whether the matching input

pair is used as two single-ended inputs or as a differential pair.

This selection is valid for all active time slots. The INP12_x and

INP78_x bits specify whether the input pair is enabled during the

corresponding time slot and, if enabled, which input is connected to

which AFE channel.

The sleep conditions are used for any inputs that are not ena-

bled. Sleep conditions are determined by the INP_SLEEP_12 and

INP_SLEEP_78 bits, which specify the state for the input pairs

during sleep and when the inputs are not active. Inputs are only

considered active during the precondition and pulse regions for time

slots where they are enabled.

Preconditioning of the sensor connected to the input is provided

to set the operating point at the input just before sampling. There

are several different options for preconditioning determined by the

PRECON_x bits. The PRECON_x bits are provided for each time

slot to specify the precondition for enabled inputs or input pairs

during the corresponding time slot. Preconditioning options include:

float the input(s), VC1, VC2, input common-mode voltage (VICM),

TIA_VREF, TIA input, and short the input pair. The preconditioning

time at the start of each time slot is programmable using the

PRE_WIDTH_x bits. The default preconditioning period is 8 µs.

The block diagram in Figure 15 shows all the bias levels that can be

switched into the input connections during sleep and precondition-

ing. These connections are not available during the sampling phase

of a time slot in which the input is selected.

Figure 15. Analog Input Multiplexer

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