Log112 (single supply operation)

Jayaram C B

Other Parts Discussed in Thread: LOG112, TPS60402, LOG114, LOG101, TPS63700, MC33063A, TPS54060, TPS84259, TPS84250

Hi,

We are looking for single supply (only positive supply) operation of Log112 logarithmic amplifier. The single supply operation depicted in the datasheet uses TPS60402DBV(negative charge pump). Please let us know if it is mandatory to use the TPS60402DBV during single supply operation of Log112 or not. If not, please let us know a typical application diagram without the same.

Thanks for your time.

Regards

Jayaram C B

over 13 years ago

0 Thomas Kuehl over 13 years ago

TI__Guru* 93105 points

Hello Jayaram,

The LOG112 is designed and specified to be operated with dual polarity supplies. The TPS60402 negative charge pump is an easy solution for generating a negative supply voltage when a single, positive supply is only available.

There is newer log amplifier, the LOG114, that is designed on a lower voltage process and can be operated from a single +5 V supply. Figure 2 in the LOG114 data sheet shows a single +5 V supply connection. The device is fully specified for +5 V operation in the Electrical Characteristics table. The LOG114 offers much versitility and you may be able to readily employ it in an application where you intended to use the LOG112.

Regards, Thomas

PA - Linear Applications Engineering

0 Jayaram C B over 13 years ago in reply to Thomas Kuehl

Intellectual 370 points

Hi Thomas,

Thanks for your reply....Is there an IC similar to Log114 available which operates at a higher voltage (say +15V) level in single supply operation and offers similar versiltility/response?

Regards,

Jayaram C B

0 Thomas Kuehl over 13 years ago in reply to Jayaram C B

TI__Guru* 93105 points

Hi Jayaram,

None of the other TI log amplifier offerings that can withstand +15 V are specifically designed for single supply operation. The pseudo-single supply solutions provided in the LOG101 - LOG112 data sheets all rely on adding a TPS, negative charge pump, to provide the negative supply. All of these log amplifiers can be used with a +15 V supply.

Regards, Thomas

PA - Linear Applications Engineering

0 Jayaram C B over 13 years ago in reply to Thomas Kuehl

Intellectual 370 points

Hi Thomas,

Thanks for your reply.The Voltage range of negative charge pump TPS60402DBV shown in Log112 and Log101 is 1.6 V to 5.5 V whereas our application needs a voltage in the range -12V to -15V.Is there any negative charge pump circuit capable of delivering till -15V. Please let us know.

Thanks for your time.

Regards,

Jayaram C B

0 Thomas Kuehl over 13 years ago in reply to Jayaram C B

TI__Guru* 93105 points

Hello Jayaram,

I am not finding a TI inverting charge pump that can operate with a operate with a +15 V supply and produce a -15 V output. If you are certain your negative supply needs to be in the -12V to -15 V range, then the only TI solutions I can suggest are PWM-based DC-DC inverters. The TPS63700 data sheet Fig. 15 shows an example of a 2.7 V to 5.5 V input, -12 V output supply. The data sheet indicates it can be set for an output voltage up to -15 V. There is the added requirement of the low input voltage because the TPS63700 cannot handle a +15 V input level. Another possibility is the MC33063A boost-buck inverting regulator. I do believe it can be configured to handle a +15 V input voltage while providing a -15 V output.

Another thopught is to check the web and see if other semiconductor manufactures can provide the +15 V to -15 V power supply solution. There may be an available 15 V charge pump solution. If so, that would likely be the easiest to apply and lowest cost solution.

Regards, Thomas

PA - Linear Applications Engineering

0 David_Daniels over 13 years ago in reply to Thomas Kuehl

TI__Mastermind 27825 points

The evm and app note may work for you. It generates a +/- output from a 24V input, but it also can work down at 5V.

Split Rail EVM

http://www.ti.com/tool/tps54060evm-590

Split Rail App note

http://www.ti.com/tool/swiftposneg-calc

0 Thomas Kuehl over 13 years ago in reply to David_Daniels

TI__Guru* 93105 points

Hello David,

Thank you for the quick reply and referenced application notes about the TPS54060 EVM. Another device that was recommended to generate the -15 V supply from a +15 V supply is the new TPS84259. These provide the LOG112 customer a couple of supply options.

Regards, Thomas

PA - Linear Applications Engineering