iC-RC1000

SIN/COS SIGNAL SAFETY MONITOR IC

Rev C2, Page 8/14

APPLICATION NOTES

Application with Series Resistors

The input pins can be loaded permanently with up to 2 mA, and this permissible maximum current determines

the resistor value of Rv. The input pins are limited to the supply voltage plus the clamp voltage Vc()hi by the

integrated clamping circuit (see Elec.Char. No. 002).

ERR

Rv

Rv

Rv

Rv

iC-RC1000

PSIN

NSIN

PCOS

NCOS

GND

VCC1

VCC2

OK

VCC2

ERR

PSIN

NSIN

PCOS

NCOS

OK

VCC1

GND

GND

Figure 3: Overvoltage protection with external resistors

In this application, the following must be paid attention to:

1. The power loss in the series resistor

2. The cut-off frequency at the input pins

The following example refers to the measurings with the evaluation board RC1D. For an overvoltage capability

of up to 36 V resistors of for instance 39 kΩ or 18 kΩ can be used. On the evaluation board the capacity of each

input pin is approximately 10 pF. The cut-off frequency can be calculated using the capacity and the selected

series resistor (Table 4).

39 kΩ

408 kHz

18 kΩ

880 kHz

Table 4: Cut-off frequency (-3 dB) with series resistor

A -3 dB cut-off frequency of 880 kHz means that the input amplitude at 500 kHz is already approximately 1 dB

lower. Concerning the amplitude monitoring this means that the error message at 500 kHz is only carried out at

a 10 % higher input amplitude.

Note: The iC’s pin capacity is approximately 5 pF; additional capacitances should be kept as low as possible if

higher frequency input signals are to be monitored.