ICS2008B Errata

1. Figure 8 “Self Biased Inputs” Diagram on page 15:

a) VDD/2 should be VDD/3

b) 5K should be 35K

2. Add the following notes called “AC Coupling of Internally-Biased Inputs” after

“Self Biased Inputs” section on page 15.

AC coupling is not recommended when the input is of large voltage swing and/or of low

frequency. If AC coupling is attempted in these cases, then great care must be taken that

the voltage at the input pin does not go below ground nor be allowed to settle near the

threshold value. In such cases, it is recommended that the input pin in question be

observed in operation with a high-impedance scope probe.

In the case of large voltage swing inputs, the ICS2008B input pin can easily be driven

below ground. This is possible because the voltage at the pin will swing around the

internally generated bias point. Driving the input pin below ground should never be

allowed and can potentially damage the device. In the case of a large input swing, a series

resistor can be placed between the coupling capacitor and the input pin to divide down

the input voltage and reduce the swing at the input pin.

In the case of low frequency signals, the coupling capacitor can become fully charged

which will allow the input slew to close to its threshold value, causing any noise to

falsely trigger the input. Low duty cycle inputs can have an effect similar to low

frequency. A larger coupling capacitor may be required. The case of a low frequency,

large amplitude input is especially dangerous because the voltage swing at the input pin is

increased by the same amount that the capacitor has charged.

As an example of the measures that may need to be taken, a 5V, 30 Hz, 50% duty cycle

signal on the Click input can be safely AC coupled to the Click pin by using a 1µF

coupling capacitor and a 100K ohm series resistor. The large time constant prevents the

capacitor from becoming fully charged and the series resistor, combined with the internal

resistor, divides down the input voltage to an acceptable swing so that the input pin is

never driven below ground.