SN5420, SNB4LS20, SN54S20 SN7420, SN74LS20, SN74S20 DUAL 4-INPUT POSITIVE-NAND G
ID: 2268122 • Letter: S
Question
SN5420, SNB4LS20, SN54S20 SN7420, SN74LS20, SN74S20 DUAL 4-INPUT POSITIVE-NAND GATES SDLS079 DECIMBER 1983-REVISED MARCH 1988 SN5420.J PACKAGE SNS4LS20. SN54520..J OR W PACKAGE SN7420...N PACKAGE SN74LS20. SN74S20...DORN PACKAGE TOP VIEW Package Options Include Plastic "Small Outline Packages. Ceramic Chip Cariers and Flat Packages. and Plastic and Ceramic DIPs . Dependable Texas Instruments Quality and Reliability descriptiorn These devices contain two independent 4 mot NAND gates The SN5420. SN54LS20, and SN54$20 are characterized for operation over the full military range of-55°C to 125 C. The SN7420, SN74LS20. and SN74520 are characterized for opertion from O C to 70°C. 2A SN5420W PACKAGE ITOP VIEW 1D 30 1C FUNCTION TABLE leach gate Vcc GND INPUTS OUTPUT A B C o 2C SN54LS20. $N54S20.FK PACKAGE TOP VIEw logic symbol 3 2 1 20 19 1A 1B 160 NC 4 28 2A-191 9 10 1112 1 (10)Explanation / Answer
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7. The SN7420 does not require a pull up resistor on its outputs. The reason is that pull up resistors are required on output only if its an open drain or open collector configuration, and the IC is neither of these.
8. The maximum pull up resistor value is chosen based on the input impedance of the device. The mentioned range of devices usually have an input impedance in the range 10K till 1M ohms. To prevent loading, it is usually desired to use a maximum of 1/10th of the above value i.e. a value of 10k ohms.
9. With 100K resistors, we can put 10 of them in parallel to achieve a value of 10K. If the value needs to be lesser, we can put more than 10 of them in parallel.
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