X9C103 changing to MAX5451 or MAX5389

Thread Starter

massanetabr

Joined Jun 3, 2019
26
Guys, I'm going to exchange a digital potentiometer X9C103 that is used connected to the RT of an SG3525.

The goal is to have more resolution, more steps since X9C103 is 100 steps and MAX5451 or MAX5389 is 256 steps.

Controlling the X9C103 today is done by a PICF628A.

The questions are as follows:

1) The Max5451 or Max5389 look the same to me, I just see that the Max5389 is a newer item, I didn't see any difference between them in relation to the X9C103, the more experienced ones tell me.
1622753251405.png1622753251405.png
2) The uc is connected to X9C103 using this board below, in which I have 4 capacitors, I believe it is one for each IC input X9C103 in relation to ground and one on vdd, am I correct?

The pins and outputs of the direct uc can I connect directly to the control pins of the IC Max5451 or Max5389, without putting a resistor or capacitor?
 

JohnInTX

Joined Jun 26, 2012
4,594
Either of the MAX parts should work OK - the interface is the same clock and direction counter setup. The main difference: X9C10x has a built in EEPROM to retain the wiper position through power off, the MAX parts you listed do not and reset the wiper to midrange on power up. The MAX parts are lower power. The MAX5389 is more accurate than either if the others. Which is best depends on your application.
As for the capacitors, normal decoupling should be sufficient. On your photo it looks like C4 is across the wiper to smooth out transitions.
Good luck!
 

Attachments

Last edited:

Thread Starter

massanetabr

Joined Jun 3, 2019
26
As an example, remembering that I am a beginner in electronics. I'm going to use MAX5389 or MAX5451 in place of the RT resistor on an SG3525. As I know, as an example, which current leaves the SG3525 and passes through the RT, and where I find in the datasheet the maximum current of the resistance of the MAX5389.
 

Irving

Joined Jan 30, 2016
2,306
The max current in/out of the resistance is dependant on which version you are using. Its specified in the Absolute Maximum section:
1623086630909.png

The current out of Rt on the SG3525 is spec'd at 2mA and the minimum value of Rt is 2kOhm. You should use a MAX5389L or MAX5389M with a 1k8 series resistor between the Rt pin and the MAX5389.
 

JohnInTX

Joined Jun 26, 2012
4,594
As an example, remembering that I am a beginner in electronics. I'm going to use MAX5389 or MAX5451 in place of the RT resistor on an SG3525. As I know, as an example, which current leaves the SG3525 and passes through the RT, and where I find in the datasheet the maximum current of the resistance of the MAX5389.
A schematic of your circuit would be most helpful.
 

Thread Starter

massanetabr

Joined Jun 3, 2019
26
The max current in/out of the resistance is dependant on which version you are using. Its specified in the Absolute Maximum section:
View attachment 240633

The current out of Rt on the SG3525 is spec'd at 2mA and the minimum value of Rt is 2kOhm. You should use a MAX5389L or MAX5389M with a 1k8 series resistor between the Rt pin and the MAX5389.
I can't use the MAX4389N or have any tips not to burn it, if I want to use it.
 

Irving

Joined Jan 30, 2016
2,306
I can't use the MAX4389N or have any tips not to burn it, if I want to use it.
I assume you meant MAX5389N. It may be possible to use it, but I need to know more about the existing circuit. The Rt resistor for the SG3525 is specified as 2k to 150k depending on the required frequency range and value of Ct; The current through Rt depends on the reference voltage which is 5.1v and is limited in output current so Rt is required to be >2k so there must be some external resistors in series with the X9C103 to ensure the minimum value is always >2k.

The X9C103 is only 10k maximum resistance, so the equivalent replacement is the MAX5389L (as per your original requirement to change from 100 steps to 256 steps). Using the MAX5389N (which is 100kOhm) would require a change to the timing capacitor Ct to retain the same oscillator frequency range so I'd need to understand how the SG3525 is being used, i.e. what is the timing capacitor Ct and are there any other components affecting how the X9C103 functions as Rt.
 
Top