AD7298BCPZ(RevPrA) データシートの表示（PDF） - Analog Devices

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AD7298BCPZ
(Rev.:RevPrA)

8-Channel, 1MSPS, 12-Bit SAR ADC with Temperature Sensor

Analog Devices 

Preliminary Technical Data

Temperature Value Format

One LSB of the ADC corresponds to 0.25°C. The temperature

reading from the ADC is stored in a 12-bit twos complement

format, to accommodate both positive and negative

temperature measurements. The temperature data format is

provided in Table 9.

Table 9. Temperature Data Format

Temperature (°C) Digital Output

−40

1111 0110 0000

−25

1111 1001 1100

−10

1111 1101 1000

−0.25

1111 1111 1111

0

0000 0000 0000

+0.25

0000 0000 0001

+10

0000 0010 1000

+25

0000 0110 0100

+50

0000 1100 1000

+75

0001 0010 1100

+100

0001 1001 0000

+105

0001 1010 0100

+125

0001 1111 0100

Temperature Conversion Formula:

Positive Temperature = ADC Code/4

Negative Temperature = (4096 - ADC Code)/4

VDRIVE

The AD7298 also has the VDRIVE feature. VDRIVE controls the volt-

age at which the serial interface operates. VDRIVE allows the ADC

to easily interface to both a 1.8V and 3V processors. For

example, if the AD7298 were operated with a VDD of 3.3V, the

VDRIVE pin could be powered from a 1.8V supply. This enables

the AD7298 to operate with a larger dynamic range with an VDD

of 3.3V while still being able to interface to 1.8V processors.

Take care to ensure VDRIVE does not exceed VDD by more than

0.3V (see the Maximum Ratings Section).

AD7298

THE REFERENCE

The AD7298 can operate with either the internal 2.5V on-chip

reference or an externally applied reference. The EXT_REF bit

in the control register is used to determine whether the internal

reference is used. If the EXT_REF bit is selected in the control

register, an external reference can be supplied through the VREF

pin. On power-up, the internal reference is enabled. Suitable

external reference sources for the AD7298 include AD780,

AD1582, ADR431, REF193, and ADR391.

The internal reference circuitry consists of a 2.5V band-gap

reference and a reference buffer. When the AD7298 is operated

in internal reference mode, the 2.5V internal reference is avail-

able at the VREF pin, which should be decoupled to AGND using a

10 μF capacitor. It is recommended that the internal reference be

buffered before applying it elsewhere in the system. The internal

reference is capable of sourcing up to TBD μA of current when

the converter is static. The reference buffer requires 10ms to

power up and charge the TBD μF decoupling capacitor during

the power-up time.

Rev. PrA | Page 15 of 18

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