TSC2012H datasheet(33/49 Pages) STMICROELECTRONICS

33 / 49 page

If a single channel is used, the change on the sample and hold capacitance is very small for sure, and so the

recovery time is extremely low as described by the figure below.

Figure 66. Capacitive load response at Vcc = 3.3 V with a step of 100 mV

-4µ

4µ

8µ

12µ

-100

-80

-60

-40

-20

100

-1000

-900

-800

-700

-600

-500

-400

-300

-200

-100

100

200

300

400

500

600

700

800

900

1000

Time (s)

Sample and hold

Vout

Vcc=3.3V, Vicm=1.65V, Vsense=0Vpp

T=25°C,

50kHz square signal of 100mV amplitude

injected in the output through 40pF

The effect of the ADC sampling and hold can be easily smoothed thanks to an RC filter. As suggested on the

schematic below. The capacitor of the external filter must be chosen much higher than the internal ADC capacitor,

in order to easily absorb the sudden voltage variation on the output due to the sampling and hold of the ADC. The

resistance must be chosen according to the application speed of the system in order not to impact the whole

application. The main advantage of using an RC filter is to have an antialiasing system. The used ADC should

certainly have sample and hold conversion in accordance with the RC filter value, in order to let the output

recover before sampling.

Figure 67. RC filter when driving ADC

In Figure 4 an Rs = 470 Ω resistance and a Ct = 470 pF capacitance have been set. Given a low-pass filter of 720

kHz and a response time of roughly 660 ns.

In Figure 5 an Rs = 820 Ω resistance and a Ct = 1 nF capacitance have been set. Given a low-pass filter of 194

kHz and a response time of roughly 2.5 µs.

TSC2010H, TSC2011H, TSC2012H

Application information

DS13791 - Rev 2

page 33/49

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