TIMING RESISTANCE for TL2842B

Rak

Intellectual 505 points

Other Parts Discussed in Thread: TL2842B, TL3842B, TL3842

Hello,

I would like to know about "TIMING RESISTANCE (RT)" for TL2842B.

Could you please help ?

My customer says he wants to use RT = 1k Ohm in his application.

Looking into "TIMING RESISTANCE vs. FREQUENCY" graph in page12 of datasheet,

SLVS610B, there are data for RT between 3k to 100k Ohm, but not for 1k Ohm.

On the other hand, "MAXIMUM OUTPUT DUTY CYCLE vs. TIMING RESISTOR" graph

shows data for 1k Ohm.

He is wondering if "1k Ohm" should not be used for RT or not.

(RT must be higher than 3k Ohm ???)

If 1k Ohm is acceptable, he wants to get TIMING RESISTANCE vs. FREQUENCY

graph with data covered for RT = 1k Ohm.

Please advise.

Thank you in advance for your help.

Best regards,

over 14 years ago

0 Ron Michallick over 14 years ago

TI__Guru**** 164456 points

Hello Rak,

The timing resistor can be as low as 800 ohms on the TL3842B. The "TIMING RESISTANCE vs. FREQUENCY" chart was inherited from the TL3842.
The TL3842B has a specified discharge current and can support lower timing resistance without wild variability in maximum duty cycle and oscillation frequency.

I will recommend that the chart be expanded to 800 ohms or possibly 1,000 ohms to keep the log chart pretty.

Regards,
Ron Michallick