LM2907-N, LM2917-N Specification

Hello Kawai,

#1. Note that the LM2917 has an internal zener diode across the power supply pins - so the maximum supply voltage would be 8V. Anything higher than 7V would require a series dropping resistor. See the "Using Zener Regulated Options" in the Apps section of the datasheet.

The LM2907 version does NOT have the supply zener or input hysteresis.

The "Total Supply Current" graph on page 7 starts at 6V. So I would say the minimum voltage is 6V. Counting Vbe's in the schematic, along with the common mode limits in the table, I would agree.

#2 and #3 - Theoretically, there is no lower limit to the frequency. The device is DC coupled throughout - so the only limit I would see is the value of R1 (See the "Choosing R1 and C1" section). The bias current of the input limits the upper value of R1. The paragraph also notes the upper frequency.

According to the first "Tachometer Linearity vs Temperature" graph, which is specified at 200Hz, it is slightly better than the second graph at 1KHz. I would expect that the linearity should get better at low frequencies as the internal device delays become a smaller part of the time constants.

Ultimate linearity will depend on the quality of the timing capacitors, as the ESR and soakage of the larger value capacitors can eat into the linearity, and the effects of bias current through R1. There is a balance of how large the capacitor can get and the upper value of R1.

Also, if you do use the zener regulation with an external series resistor, be sure to add a supply bypass capacitor at pin 6 of at least 2-5x the value of the timing capacitor to provide a charge reservoir to charge the timing capacitor. Otherwise the V+ pin can "droop" as C1 charges - changing the threshold points and affecting the linearity.

Regards,

Paul-san,

Thank you for the answer.

Could you please tell me the total supply current for this device, LM2907-N and LM2917-N ?

I found that there is Total Supply Current written in the datasheet P.4 ZENER REGULATOR,

but, I think this value is for only zener diode and does not include the device supply current.

Additionally, is there any other document for these device other than AN-162(SNAA088) ?

It would be a great help if there is a detail design guide.

Hello Kawai-san,

There is a "Total Supply Current" vs supply graph on page 7. This looks to be the actual device current as it is linear down to 6V, I would expect to see a step between 6 and 7V if the Zener current was included. The graph shows about 3.6mA at 12V, which would agree with the table value.

The zener should add another 1-2mA on top of the curve with proper series resistor selection.

TI also has a datasheet for their non -N version, but it is much shorter and covers the same basic info:

 http://www.ti.com/lit/gpn/lm2907

I am not aware of any other documentation other than the datasheet and the appnote. Googling around just shows a lot of stashed copies of the datasheet and some interesting home-brew anemometer circuits...

Regards,

Hello Paul Grohe / Kawai-san,

We have used LM2917 Frequency to Voltage Converter in our design to convert 50Hz-170Hz frequency signals having 100mV to 350mV amplitude to voltage.

We are not getting any voltage at output when input above signal. The supply voltage we are using is 5/8V with 470E series resistor. In circuit design we have choose R1=240K, C1=0.039uF and C2=1uF. WHY? What should be the output voltage?

When we are giving input frequency signal (50Hz to 170Hz) having increased amplitude voltage (above 340mv), we able to get output voltage proportional to input frequency signal.

Could you  tell us that What is the recommended input frequency amplitude range, MIN,MAX and peak to peak for LM2907 and LM2917?

What would be recommended value of R1, C1 and C2 parts to convert 50Hz-170Hz frequency signals having 100mV to 350mV amplitude to voltage. What other changes are recommednded in below design? Consider VIN=5V

I missed to mentioned that we are using 12V DC car battery input and giving same signal as input to pin#1 of LM2917 through DC block capacitor -Ceramic 100nF/50V. What is recommended value/type of DC block capacitor?

Regards,

Narayan Kunapara