Sharing of experience in single board circuit design 3-selection of pull-up and pull-down resistor parameters

tiankai001

Sharing of experience in single board circuit design 3-selection of pull-up and pull-down resistor parameters [Copy link]

3. Pull-up resistors and pull-down resistors

Let's first take a look at the selection principles of pull-up resistors and the selection of pull-up resistor resistance values.

1. Selection principles of pull-up resistors

A. Improve the ability to sink current

[color=rgb(34, 34, The power consumption and driving capability of the devices inside the single board are different. Therefore, the current sinking capability of the devices when connected is different, and there will be driving problems in the connection.

B. Level compatibility

The device selection within or between boards is different, and the signal level characteristics are different. For compatibility considerations, pull-up resistors need to be added to ensure compatibility. C. Electrical stability characteristics Some devices require that the initial electrical levels of certain pins be fixed at a high level when powered on. At this time, a pull-up resistor must be added to ensure that the device can work normally.

D. Device and parameter selection

For the above two situations A and B, the general pull-up resistor is selected from 2K~1M ohm, depending on the load situation. When the load is heavy, the resistance should be close to the lower limit, and when the load is light, the upper limit should be selected. The load here is determined by the device power consumption index. For the above-mentioned C situation, it is determined by the data characteristics of the device. The device is generally based on a metal film resistor or resistor array.

2. Principles for selecting pull-down resistors

Let's take a look at the principles for selecting pull-down resistors and the resistance value of pull-down resistors.

A. Level compatibility

The selection of devices within or between boards is different, and the signal level characteristics are different. For compatibility considerations, pull-up resistors need to be added to ensure compatibility.

B. Termination

[color=rgb(34, 34, When the signal frequency within or between boards is high or the rising edge is steep, a termination resistor needs to be added to pull it down to ground. Generally, an appropriate capacitor is often connected in series.

C. Characteristics of electrical stability

Some devices require that the initial level of certain pins be fixed to a low level when powered on. At this time, a pull-down resistor must be added to ensure that the device can work normally.

D. Device and parameter selection

For the above A situation, the general pull-down resistor is 1K~100K ohms, depending on the load situation. For CMOS level load, the resistor should be close to the lower limit, and the upper limit should be selected for TTL level. The level here is determined by the load index. For the above B situation, a 75~150 ohm resistor is generally selected; for the above C situation, it is determined by the data characteristics of the device. The device is generally based on a metal film resistor or resistor array.

btty038

The microcontroller is better.

tiankai001

btty038 posted on 2019-1-8 10:58 MCU is better at using,

Hardware determines software, MCU experts are generally also very proficient in circuits

btty038

tiankai001 posted on 2019-1-8 11:13 Hardware determines software. Microcontroller experts are generally also very proficient in circuits

It is true that only a good platform can produce good things