TLV5620 DAC design analog connection to pic

ddorling · Joined: 24 Dec 2007 Posts: 13

Hi
The TLV5620 is a popular low cost 4 channel 8 bit DAC. When interfacing the outputs to the analog inputs of a pic is it necessary to use a load resistor (10k) to ground on each channel or can it be left out and made a straight connect. Maybe one of you EE folk would know. How would you make the connection to the pic and what is the reason.

THNXS
ddorling

mkuang · Joined: 14 Dec 2007 Posts: 257

The datasheet doesn't seem to suggest a 10k resistor. Usually the output of a DAC just connects straight to the analog input of a PIC. Where did you get the resistor idea?

ddorling · Joined: 24 Dec 2007 Posts: 13

Hi, thanks for your response
In the datasheet for the TLV5620
SLAS110B – JANUARY 1995 – REVISED APRIL 1997

fig12 shows an output buffering scheme having the TLV output connected to a voltage follower. A 10k load resistor to ground is connected to the TLV output. I don't know the electrical difference between the + op amp input and the analog input but I made a wild assumption that what is good for the op amp is good for the analog input. I thought maybe the analog input likes to see a running current. I also thought that maybe it would help in protecting the analog input from over current strain in the case when it is set up as a digital input before the app is initialized or when debugging the app. I have used both ways for much time and haven't had any trouble. The purpose of my question is for commiting to a production design and four less resistors is great in anyones $book. So is there any electrical basis for keeping them in the design. From your response I'm hedging toward NO, trash them.

mkuang · Joined: 14 Dec 2007 Posts: 257

The functional block diagram shows that the outputs are already buffered. However, each channel can only drive a 10k load which means it can only sink or source 1mA of current. If you want to drive a more hefty load then you can use the scheme shown in figure 12, otherwise just connect the output directly to the PIC.

ddorling · Joined: 24 Dec 2007 Posts: 13

Hi
Yes, that makes perfect electrical sense. Thanks for clearing up that point for me.
best wishes