LM7171

Athul Mallappallil

Other Parts Discussed in Thread: LM7171, SN65HVD101, SN65HVD102, LM393, LM8272, TINA-TI

Hello

I want to make a logic translator from TTL level to 0-12/24V signals.
The signal frequencies can be as high as 1MHz. and high level of the signal can be between 8 to 32V. It must be capable of giving a current up to 100mA(maximum for both source and sink). The load can be capacitive inductive etc.. The output impedance should be as low as possible (<50 Ohms). More importantly, the output short be short circuit protected(short to bat and short to ground) for infinite time duration
Kindly menition the LM7171 IC will satisfy the above criteria. If not, how it can be done or is there any other product which does this

Thanking you..

over 10 years ago

0 Miguel Robertson over 10 years ago

TI__Guru 62920 points

Hi Athul,

I'll move this post to the High Speed Amplifiers forum, since they should be able to give better guidance with regard to LM7171. In addition, you may want to take a look at the SN65HVD101 and SN65HVD102 devices. These can support the voltage levels from 9 V to 30 V and currents beyond 100 mA (with a configurable limit so that short-circuits to power/ground can be tolerated), although they cannot operate at the 1-MHz rate that you mentioned (250 kbps is the maximum rate).

Regards,
Max

0 Hooman Hashemi over 10 years ago in reply to Miguel Robertson

TI__Mastermind 22825 points

Hi Athul,

The LM7171 has the slew rate (> 3,100 V/us) to support your 1MHz toggle rate.

Regarding the 100mA output current needed: From Figure 7, I'd say that providing 100mA typical output current requires output swing to be restricted to 4V from each rail (+/-11V with Vs= +/-15V). That means even if you operate the LM7171 with a total supply voltage of 35V, you could only support this heavy load up to 27Vpp. I am not sure this is adequate for your application?

You could boost the output current significantly if you used a Class A-B stage on the output, similar to this taken from:

Regards,

Hooman

0 Athul Mallappallil over 10 years ago in reply to Hooman Hashemi

Prodigy 20 points

Dear Hooman,
Thanks for the reply...
Info provided is really valuable...

I intend to get a min of 8V if the supply is 9V or 22V when supply is 24V. The current rating for the normal operation never goes beyond 60mA. Regarding the frequency, I can have a PWM of upto 2KHz or a square wave of max frequency 50Khz... What I really worried about is the short condition to Ground and short condition to Bat... If it is possible to get this done in a single IC. it will be great... I was actually planning to uses comparator LM393. But I don't think it is protected against short circuit and current rating seems to be low.
Kindly mention if there is any IC which serves the purpose...
More over the IC should be passive, in the sense we don't want a any additional control on the IC. It should be signal translator...
Thanking you...
Athul M

0 Hooman Hashemi over 10 years ago in reply to Athul Mallappallil

TI__Mastermind 22825 points

Hi Athul,

Your best bet would be to use the LM8272. From the plots below, your 60mA output current requirement means the typical output swing would be about 1V from either rail (e.g. 23V with 24V supply):

Regards,

Hooman

0 Hooman Hashemi over 10 years ago in reply to Hooman Hashemi

TI__Mastermind 22825 points

Hi Athul,

For protection against short circuit condition, you may have to devise an external protection, as shown below. This circuit will limit the output current to ~83mA (=0.6V/ 7.1ohm) sourcing. It works by removing the input condition that causes the output current to cause protection transistor (T1) VBE On condition:

Here is the TINA-TI circuit for your reference:

LM8272 with currnet limit protection 7_20_15.TSC

Regards,

Hooman