SCLS789B January 2020 – October 2026 SN74HCS10
PRODUCTION DATA
The SN74HCS10 includes inputs with positive clamp diodes. The positive clamp diodes prevent the input voltage from reaching levels dangerous to the device, holding the input voltage (VA) to approximately VCC + 0.5V as long as the input clamp current (IIK) does not exceed the maximum limit provided in Absolute Maximum Ratings.
The input can draw significant current when the input voltage (VA) exceeds the supply voltage (VS) because the diode is forward biased and must be externally limited to avoid damage to the device. Additionally, the input clamp current, IIK, can be several orders of magnitude larger than ICC, resulting in current returning to the supply (the reverse of normal operation) which must be accounted for by the system designer, as shown in Figure 7-2.
A resistor (R) can be used to prevent excessive current on the input as shown in Figure 7-2. The resistor value can be determined with R ≥ (VIN - VA)/IIK(max), with VA ⋍ VS + 0.5V. The system-level input voltage (VIN) can exceed the supply voltage (VS) because the device input voltage (VA) is held at approximately VS + 0.5V by the clamp diode.