EVAL-AD7291SDZ(Rev0) 查看數據表（PDF） - Analog Devices

零件编号

产品描述 (功能)

生产厂家

EVAL-AD7291SDZ
(Rev.:Rev0)

8-Channel, I2C, 12-Bit SAR ADC with Temperature Sensor

Analog Devices 

AD7291

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 tempera-

ture measurements. Sample temperature values are listed in

Table 7. The temperature conversion formulas are as follows:

Positive Temperature = ADC Code/4

Negative Temperature = (4096 − ADC Code)/4

The previous formulae are for a VREF of 2.5 V only. If an

external reference is used, the temperature sensor requires an

external reference of between 2 V and 2.5 V for correct

operation. The temperature results (in Celsius) are calculated

using the following formula, where VEXT_REF is the value of the

external reference voltage.

Temperature

=

VEXT

_

REF

⎜⎛

⎝

ADCCode

10

+

109.3⎟⎞

⎠

−

273.15

Table 7. 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

VDRIVE

VDRIVE controls the voltage at which the serial interface operates.

VDRIVE allows the ADC to easily interface to both 1.8 V and 3 V

processors. For example, if the AD7291 is operated with a VDD

of 3.3 V, the VDRIVE pin can be powered from a 1.8 V supply.

This enables the AD7291 to operate with a larger dynamic

range with a VDD of 3.3 V while still being able to interface to

1.8 V processors. Take care to ensure that VDRIVE does not

exceed VDD by more than 0.3 V (see the Absolute Maximum

Ratings section).

THE INTERNAL OR EXTERNAL REFERENCE

The AD7291 can operate with either the internal 2.5 V on-chip

reference or an externally applied reference. The EXT_REF bit

in the command register is used to determine whether the

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

command 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 AD7291

include AD780, AD1582, ADR431, REF193, and ADR391.

The internal reference circuitry consists of a 2.5 V band gap

reference and a reference buffer. When the AD7291 operates in

internal reference mode, the 2.5 V internal reference is available

at the VREF pin, which should be decoupled to GND1 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 2 mA of

current when the converter is static. The reference buffer

requires 5.5 ms to power up and charge the 10 μF decoupling

capacitor during the power-up time.

RESET

The AD7291 includes a reset feature, which can be used to reset

the device and the content of all internal registers including the

command register to their default state. To activate the reset

operation, the PD/RST pin should be brought low for a

minimum of 1 ns and a maximum of 100 ns and be asynchronous

to the clock; therefore, it can be triggered at any time. If the PD/

RST pin is held low for greater than 100 ns, the part enters full

power-down mode. It is imperative that the PD/RST pin be held

at a stable logic level at all times to ensure normal operation.

Rev. 0 | Page 14 of 28

Share Link: