AD7151BRMZ-REEL Datasheet AD7151BRMZ, AD7151BRMZ-REEL | P13-P15

AD7151

Rev. 0 | Page 12 of 28

SENSITIVITY

In adaptive threshold mode, the output comparator threshold is

set as a defined distance (sensitivity) above the data average,

below the data average, or both, depending on the selected

threshold mode of operation (see

Figure 29). The sensitivity

value is programmable in the range 0 to 255 LSBs of the 12-bit

CDC converter (see the

NEGATIVE

THRESHOLD

POSITIVE

THRESHOLD

DATA AVERAGE

OUTPUT ACTIVE

TIME

SENSITIVITY

DAT

SENSITIVITY

7086-019

Figure 29. Threshold Sensitivity

HYSTERESIS

In adaptive threshold mode, the comparator features hysteresis.

The hysteresis is fixed to one-fourth of the threshold sensitivity

and can be programmed on or off. The comparator does not

have hysteresis in the fixed threshold mode.

OUTPUT

POSITIVE

THRESHOLD

DATA AVERAGE

OUTPUT ACTIVE

TIME

HYSTERSIS

DAT

07086-020

Figure 30. Threshold Hysteresis

TIMEOUT

In the case of a large, long change in the capacitive input, when

the data average adapting to a new condition may take too long,

a timeout can be set.

The timeout becomes active (counting) when the CDC data

goes outside the band of data average ± sensitivity. When the

timeout elapses (a defined number of CDC conversions is

counted), the data average (and thus the threshold) is forced to

follow the new CDC data value immediately (see

Figure 31).

The timeout can be set independently for approaching (for change

in data toward the threshold) and for receding (for change in data

away from the threshold). See

Figure 32, Figure 33, and the

DATA AVERAGE

+ SENSITIVITY

LARGE CHANGE IN DATA

DATA AVERAGE

– SENSITIVITY

TIME

TIMEOUT

07086-021

Figure 31. Threshold Timeout After a Large Change in CDC Data

INPUT CAPACITANCE

THRESHOLD

OUTPUT

DATA AVERAGE

OUTPUT ACTIVE

TIME

TIMEOUT APPROACHING

07086-022

Figure 32. Approaching Timeout in Negative Threshold Mode

Shortens False Output Trigger

INPUT

CAPACITANCE

LARGE CHANGE

THRESHOLD

OUTPUT

OUTPUT ACTIVE

TIME

TIMEOUT RECEDIN

07086-023

Figure 33. Positive Timeout in Negative Threshold Mode

Shortens Period of Missing Output Trigger

AD7151

Rev. 0 | Page 13 of 28

AUTOCAPDAC ADJUSTMENT

In adaptive threshold mode, the part can dynamically adjust the

CAPDAC to keep the CDC in an optimal operating capacitive

range. When the AutoDAC function is enabled, the CAPDAC

value is automatically incremented when the data average

exceeds three-fourths of the CDC full range, and the CAPDAC

value is decremented when the data average goes below one-

fourth of the CDC full range. The AutoDAC increment or

decrement step depends on the selected CDC capacitive input

range. See the

Setup Register section.

POWER-DOWN TIMER

In power sensitive applications, the AD7151 can be set to

automatically enter power-down mode after a programmed

period of time in which the output has not been activated. The

AD7151 can be then returned to a normal operational mode

either via the serial interface or by the power supply off/on

sequence.

POWER SUPPLY MONITOR

When the AD7151 V

power supply voltage drops below a

defined level needed for correct CDC operation, the on-chip

power supply monitor stops the adaptive threshold logic and

holds it in reset. After the V

reaches the required level, the

threshold logic is released, and the data average is reset to the

value of the first conversion finished at the correct power supply

voltage.

This feature prevents the adaptive threshold from being set

incorrectly after a very slow rise of the V

voltage or from being

corrupted by accidental drops in the V

voltage.

The other AD7151 functions continue working below the

power supply monitor threshold, down to approximately

1.0V..1.8V, the exact level depending on the manufacturing

process variation. In the region of the low V

voltage, the part

is still accessible via the serial interface and continues conversion.

However, the conversion results may be incorrect and,

therefore, the data should not be considered valid if the part

operates below the power supply monitor threshold.

The status of the power supply monitor can be determined by

reading the PwrDown bit in the AD7151 status register.

AD7151

Rev. 0 | Page 14 of 28

Table 5. Register Summary

Pointer Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

PwrDown – –

DacStep

OUT – –

RDY

Status 0 0x00 R

0 1 0 1 0 0 1 1

Data High 1 0x01 R 0x00

Data Low 2 0x02 R 0x00

– 3 0x03 R 0x00

– 4 0x04 R 0x00

Average High 5 0x05 R 0x00

Average Low 6 0x06 R 0x00

– 7 0x07 R 0x00

– 8 0x08 R 0x00

Sensitivity (in adaptive threshold mode)/Threshold High Byte (in fixed threshold mode)

Sensitivity

Threshold High

9 0x09 R/W

0x08

Timeout (in adaptive threshold mode)/Threshold Low Byte (in fixed threshold mode)

Timeout

Threshold Low

10 0x0A R/W

0x86

RngH RngL –

Hyst

ThrSettling (4-bit value)

Setup 11 0x0B R/W

0 0 0 0 0x0B

– 12 0x0C R/W 0x00

– 13 0x0D R/W 0x00

– 14 0x0E R/W 0x00

ThrFixed ThrMD1 ThrMD0 EnConv – MD2 MD1 MD0

Configuration 15 0x0F R/W

0 0 0 1 0 0 0 1

– – Power-Down Timeout (6-bit value)

Power-Down Timer 16 0x10 R/W

0 0 0x00

DacEn DacAuto DacValue (6-bit value)

CAPDAC 17 0x11 R/W

1 1 0x00

– 18 0x12 R/W 0x00

Serial Number 3 19 0x13 R Serial Number – Byte 3 (MSB)

Serial Number 2 20 0x14 R Serial Number – Byte 2

Serial Number 1 21 0x15 R Serial Number – Byte 1

Serial Number 0 22 0x16 R Serial Number – Byte 0 (LSB)

Chip ID 23 0x17 R Chip Identification Code

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P27 P28-P29

AD7151BRMZ-REEL

Mfr. #:

Buy AD7151BRMZ-REEL

Manufacturer:

Analog Devices Inc.

Description:

Data Acquisition ADCs/DACs - Specialized 1-CH Cap Proximity Sensor Inter IC

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AD7151BRMZ-REEL

AD7151BRMZ-REEL

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