TS7003 datasheet(9/14 Pages) TOUCHSTONE

9 / 14 page

TS7003

TS7003DS r1p0

Page 9

RTFDS

process, the input side of CHOLD is switched back to

AIN so as to be charged to the input signal again.

An A C’s acquisition time is function of how fast its

input capacitance can be charged. If an input signal’s

driving-point

source

impedance

high,

the

acquisition time is lengthened and more time must be

allowed between conversions. The acquisition time

(tACQ) is the maximum time the ADC requires to

acquire the signal and is also the minimum time

needed for the signal

to be acquired. The TS7003’s

acquisition time is calculated from the following

expression:

tACQ = 9 x (RS + RIN) x 10pF

where RIN = 100Ω (the TS7003’s internal track/hold

switch resistance), RS = the input signal’s source

impedance, and tACQ is never less than 625ns.

Because of the input structure of the TS7003,

sources with output impedances of

1kΩ or less do not

affect

significantly the

performance

the

TS7003. The TS7003 can still be used in applications

where the source impedance is higher so long as a

0.01μF capacitor is connected between the analog

input and G

. Limiting the A C’s input signal

bandwidth, the use of an external, input capacitor

forms an RC filter with the input’s source impedance.

Input Bandwidth Considerations

Since the TS7003

’s input track-and-hold circuit

exhibits a 10 MHz small-signal bandwidth, it is

possible to measure periodic signals and to digitize

high-speed transient events with signal bandwidths

higher than the TS7003

’s sampling rate by using

undersampling techniques. To avoid the aliasing of

high-frequency signals into the frequency band of

interest, the use of external anti-alias filter circuits

(discrete or integrated) is recommended. The time

constant of the external anti-alias filter should be set

so as not to interfere with the desired signal

bandwidth.

Analog Input Protection

The TS7003 incorporates internal protection diodes

that clamp the analog input between VDD and GND.

These internal protection diodes allow the AIN pin to

swing from GND - 0.3V to VDD + 0.3V without causing

damage to the TS7003. However, for accurate

conversions near full scale, the input signal must not

exceed VDD by more than 50mV or be lower than

GND by 50mV.

If the analog inputs can exceed 50mV beyond the

supplies, then the current in the forward-biased

protection diodes should be limited to less than

2mA

since

large

fault

currents

can

affect

conversion results.

Internal Reference Considerations

The TS7003 has an internal voltage reference that is

factory-trimmed to 2.5V. The internal reference output

is connected to the REF pin and is also connected to

the A C’s internal C AC. The REF output can be

used as a reference voltage source for other

components external to the ADC and can source up

750μA. To maintain conversion accuracy to within

1 LSB, a 4.7μF capacitor from the REF pin to G

recommended. While larger-valued capacitors can be

used to further reduce reference wide-band noise,

larger capacitor values can increase the TS7003

’s

wake-up time when exiting from shutdown mode (see

the “Using SH

to Reduce Operating Supply

Current” section for more information). When in

shutdown

(that

is,

when

= 0), the TS7003

’s internal 2.5-V reference is

disabled.

Serial Digital Interface

Initialization

after

Power-Up

and

Starting

Conversion

If the

pin is not driven low upon an initial, cold-

start condition, it may take up to 2.5ms for a fully-

discharged 4.7μF reference bypass capacitor to

provide adequate charge for specified conversion

accuracy. As a result, conversions should not be

initiated during this reference capacitor charge-up

delay. To initiate a conversion, the

CS pin is toggled

(or driven) low. At the

CS’s falling edge, the TS7003’s

internal track-and-hold is placed in hold mode and a

conversion is initiated. Data can then be transferred

out of the ADC using an external serial clock.

TS7003 Datasheet(PDF) 9 Page - Touchstone Semiconductor Inc

TS7003 Datasheet(HTML) 9 Page - Touchstone Semiconductor Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Datasheet Download

Link URL