ADS7870

SBAS124C − DECEMBER 1999 − REVISED DECEMBER 2005

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4

ELECTRICAL CHARACTERISTICS

For the Total System (1), −40

°C ≤ TA ≤ 85°C, VDD = 5 V, BUFIN = 2.5 V (using external reference), 2.5-MHz CCLK and 2.5-MHz SCLK (unless

otherwise noted).

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

Digital Outputs

Data coding

Binary 2s complement

Low-level output voltage, VOL

ISINK = 5 mA

0.4

V

Logic levels

Low-level output voltage, VOL

ISINK = 16 mA

0.8

V

Logic levels

High-level output voltage, VOH

ISOURCE = 0.5 mA

VDD − 0.4

V

High-level output voltage, VOH

ISOURCE = 5 mA

4.6

V

Leakage current

Hi-Z state, VO = 0 V to VDD

1

µA

Output capacitance

5

pF

Voltage Reference

Bandgap voltage

VREF = 2.048 V, 2.5 V

Pin 26 used as output,

Use internal OSC or external

−0.25

±0.05

0.25

%FSR

Bandgap voltage

reference

VREF = 1.15 V

Use internal OSC or external

CCLK as conversion clock

1.15

V

Output drive

±0.6

µA

Reference Buffer

Input voltage, BUFIN

0.9

VDD − 0.2

V

Input impedance, BUFIN

At pin 27

1000||3

G

Ω||pF

Input offset

−10

±1

10

mV

Output voltage accuracy vs temperature,

(2) (3)

Pin 28 used as output,

−0.25

±0.05

0.25

%FSR

Output voltage accuracy vs temperature,

BUFOUT/REFIN (2) (3)

Pin 28 used as output,

VREF = 2.048 V and 2.5 V

10

50

ppm/

°C

Output drive, BUFOUT/REFIN

20

mA

Power Supply Requirements

Supply voltage

2.7

5.5

V

(2)

1-kHz Sample rate

REF and BUF on, Internal os-

cillator on

0.45

mA

Power supply current (2)

50-kHz Sample rate

REF and BUF on, External

CCLK

1.2

1.7

mA

Power down

REF, BUF, Internal

oscillator off

1

µA

(2)

1-kHz Sample rate

REF and BUF on, Internal

oscillator on

2.25

mW

Power dissipation (2)

50-kHz Sample rate

REF and BUF on, External

CCLK

6

8.5

mW

Power down

REF and BUF off

5

µW

Temperature Range

Operating free-air

−40

85

°C

Storage range

−65

150

°C

Thermal resistance,

QJA

65

°C/W

(1) The specifications for the total system are overall analog input to digital output specifications. The specifications for internal functions indicate

the performance of the individual functions in the ADS7870.

(2) REF and BUF contribute 190 µA and 150 µA (950 µW and 750 µW) respectively. At initial power up the default condition for both REF and BUF

functions is power off. They can be turned on under software control by writing a 1 to D3 and D2 of register 7, REF/OSCILLATOR CONTROL

register.

(3) For VDD < 3 V, VREF = 2.5 V is not usable.