ISL73141SEH

5. Applications Information

R34DS0012EU0402 Rev.4.2

Page 23 of 27

Feb 23, 2023

5.9

Analog Input (AIN) Pin

The ISL73141SEH supports single-ended input drive only. IMPORTANT: Ensure that proper grounding

techniques and supply decoupling are used in circuit board layout to achieve optimum performance. The

ISL73141SEH evaluation board can be used as a guide for proper circuit optimization. The analog input is a

high-impedance input that exhibits a capacitive load of approximately 15pF during sample mode and 3pF during

hold mode. Due to the high bandwidth (50MHz) of the analog input, Renesas recommends using an Anti-Alias

Filter (AAF) appropriate for the desired application. It is not required to operate the ISL73141SEH with an input

amplifier, but it can improve performance and/or provide gain in certain applications. An example topology is given

in Figure 56, which uses a driver amplifier and an RC input filter. Care must be taken to choose an amplifier with

low noise and distortion because the ADC performance is directly impacted. It is also important to choose

feedback resistance values that are less than 1kΩ (typically, 100Ω to 200Ω) to minimize the impact of resistor

thermal noise. The noise of the resistor is directly related to its value by Equation 2.

where

• k = Boltzmans constant (1.38 x 10-23)

• T = Temperature in Kelvin (room temperature = 27°C = 300K)

• R = Resistance value

At the input to the ADC, a simple RC filter should be sufficient for most applications. Choose the RC circuit values

appropriately for the application. A low-value resistor (RS ≤ 50) is recommended for low noise performance. Add a

high-quality shunt capacitor (CP) as close as possible to the AIN pin to shunt charge kickback from the ADC

during sampling and to limit the input bandwidth to the ADC. The recommended values for the CP range is from

220pF to 680pF. Larger values for CP can be used for slower conversion rates.

Due to the switched capacitance of the analog input, Renesas recommends limiting series inductance in the

analog input path, particularly the inductance near the analog input pins of the device. Renesas also recommends

using a high quality ceramic capacitor (CP) in shunt on the analog input that is at an appropriate value for the

required application. Choose the series resistance in the analog input circuit based on the output impedance of

the driver amplifier and the application requirements. An example topology is given in Figure 57, which converts a

0V input common-mode voltage to the ADC input common-mode voltage of VREF/2. This circuit is employed on

the ISL73141SEH evaluation board to allow the ADC to be driven from various types of signal generators.

Figure 56. ISL73141SEH Analog Input Amplifier Example Circuit

(EQ. 2)

Power Spectral Density (PSD)

4kTR V2 Hz





=

Analog

Input

+

-

AIN

GND

ISL73141SEH

RS

CP