LM2917-N: LM2917-8

user5940158

Part Number: LM2917-N
Other Parts Discussed in Thread: LM2907-N

Hi team,

I have a question about Figure 15. (Minimum Component Tachometer Diagram) of the datasheet.www.ti.com.cn/.../lm2917-n.pdf

If I change the VCC from 15V to 5V，Can I use formula VO = VCC × fIN × C1 × R1 to calculate the output voltage？If not, what formula should be used？

over 3 years ago

0 Raymond Zhang1 over 3 years ago

TI__Mastermind 48076 points

Hi user5940158,

You may use the same formula, however, you may have to adjust R1 and C1 per design requirements. Also see Section 10.2.1.2.1 and equation 7, since I do not know what is maximum frequency you are going to have.

Enclosed is a Tina simulation that you can play around. you have to change the parameters accordingly. It was designed for 24V input voltage. BTW, if you are using 5V only, yo may use LM2907-N instead, since you are not using zener option described in section 10.2.1.2.2.

/cfs-file/__key/communityserver-discussions-components-files/14/LM2907_5F00_F2V-06032020.TSC

/cfs-file/__key/communityserver-discussions-components-files/14/LM2917_2D00_14-E2E-06032020.TSC

If you have any questions, please let us know.

Best,

Raymond

0 user5940158 over 3 years ago in reply to Raymond Zhang1

Intellectual 660 points

Hi ,Raymond

Good Day.

I am using Zener Regulated Options,I refer to Figure 19 to design my circuit and I add 470 ohm resistance between Vcc and 6 pin.

When I use formula VO = VCC × fIN × C1 × R1 and calculate at VCC = 7.6 V, the F / V value was matched.

Is that right? Please let me know.

0 Raymond Zhang1 over 3 years ago in reply to user5940158

TI__Mastermind 48076 points

Hi user5940158,

If you are using zener option, Vcc has to be greater than 7.56V, likely > approx. 9V. Otherwise, zener option will not regulate the Vcc dc voltage variations. Therefore, you can not use Vcc = 5V nominal, then supply rail is going to vary with Vcc, and Zener is not doing its work.