TS7001 datasheet(11/20 Pages) TOUCHSTONE

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TS7001

TS7001DS r1p0

Page 11

RTFDS

Typical Application Circuit

Figure 4 shows a typical application circuit for the

TS7001 where the

ADC’s GND pin is connected to

the analog ground plane of the system. In this

application circuit, the TS7001 has been configured

for two-channel operation so

the ADC’s VREF is

internally connected to VDD; as a result, the analog

input range on either analog input is 0V to VDD. It is

always considered good engineering practice to

bypass the ADC’s VDD with good quality capacitors

with short leads (surface-mount components are

preferred) and located a very short distance from the

ADC. The conversion result at the DOUT pin is a 16-

bit word with four leading zeros followed by the MSB

the

12-bit

conversion

result.

low-power

applications,

automatic-power-down-at-the-end-of-

conversion modes (PM Modes 3 or 4) should be

used to improve

the ADC’s power consumption-

versus-throughput rate performance. For additional

information

the

TS7001

’s

four

power

management operating modes, please consult the

Operating Modes section of the datasheet.

Analog Input Details

An equivalent circuit of the analog input structure of

the TS7001 is illustrated in Figure 5 where diodes

D1 and D2 serve as ESD-clamp protection for the

analog inputs. Since there are diodes from the

analog input to both VDD and GND, it is important

any forward conduction of current in D1 or D2 is

avoided. Thus, the analog input signal should never

exceed the either VDD or GND by more than

200mV. Even though the maximum current these

diodes can conduct without causing irreversible

damage to the ADC is 20mA, any small amount of

forward diode current into the substrate because of

an overvoltage condition on an unselected channel

can cause inaccurate conversion results on the

selected channel.

Attributed to parasitic package pin capacitance,

capacitor C1 in Figure 5 is typically about 1 pF.

Resistor R1 is the equivalent series resistance of the

TS7001

’s input multiplexer and input sampling

switch and is approximately 100

Ω. Capacitor C2 is

the ADC sampling capacitor and has a typical

capacitance of 10 pF.

In signal-acquisition (or ac) applications, the use of

an external R-C low-pass filter on either or both

analog inputs can be useful in removing out-of-band

high-frequency components from the analog input

signal. In applications where harmonic distortion and

signal-to-noise ratio performance are important, the

analog input(s) should be driven from a low-

impedance source. Large source impedances will

affect significantly the TS7001

’s ac performance. To

lower the driving-point impedance level, it may be

necessary to use an input buffer amplifier. The

optimal choice for the external drive op amp will be

determined by application requirements as well as

the TS7001

’s dynamic performance.

When the analog input is not driven by an external

amplifier, the driving-point source impedance should

be low. The maximum source impedance will

depend upon the amount of total harmonic distortion

(THD) that can be tolerated in the application. THD

will increase as the source impedance increases

Figure 4: TS7001's Typical Application Circuit.

Figure 5:

TS7001’s Analog Input Equivalent Circuit.

INPUT FREQUENCY - kHz

VDD = 3V

3V Ext VREF

-65

-75

-85

-90

0.2 10

-60

Figure 6: TS7001 THD vs Analog Input Frequency

RIN = 50

Ω, CIN = 2.2nF

RIN = 10

Ω, CIN = 10nF

-70

-80

20 30

60 70

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