TLV2541, TLV2542, TLV2545

2.7 V TO 5.5 V, LOW POWER, 12-BIT, 200 KSPS,

SERIAL ANALOG-TO-DIGITAL CONVERTERS WITH AUTOPOWER DOWN

SLAS245 –MARCH 2000

21

POST OFFICE BOX 655303

APPLICATION INFORMATION

FS

TLV2541

TMS320 DSP

XF

RXD

SCLK

Ain

10 k

Ω

VDD

SDO

SCLK

VDD

GND

10 k

Ω

CS

EXT

Reference

VREF

CS/FSD

TLV2542/5

TMS320 DSP

XF

RXD

SCLK

AIN 0/AIN (+)†

10 k

Ω

VDD

SDO

SCLK

VDD

GND

10 k

Ω

EXT

Reference

VREF

AIN 1/AIN (–)†

† For TLV2545 only

Figure 30. Typical Interface to a TMS320 DSP

simplified analog input analysis

Using the equivalent circuit in Figure 31, the time required to charge the analog input capacitance from 0 to Vs

within 1/2 LSB can be derived as follows.

The capacitance charging voltage is given by:

Vc

+ Vs 1–EXP

–tch

Rt

Ci

Where:

Rt = Rs + Zi

tch = Charge time

(1)

The input impedance Zi is 0.5 k

Ω at 5 V, and is higher (~ 0.6 kΩ) at 2.7 V. The final voltage to 1/2 LSB is given

by:

Vc (1 2 LSB)

+ Vs–

Vs

8192

(2)