# Part review – Linear Technology LT1302 DC/DC step-up converter

In today’s part review, we have a look at the Linear Technology LT1302. This is a fascinating part as it can increase a supply voltage and still maintain a reasonable current. For example, with a supply voltage of 2 volts the LT1302 can give you 5V at 600 mA or 12V at 150 mA. That’s pretty awesome, and can save you a lot of space when designing products, such as reducing the number of cells required in a battery pack. One example of such a product is the very popular mintyboost battery pack booster by Limor Fried.

But first as usual, let’s say hello…

There are two versions of this part, the LT1302 which allows a variable output; and the LT1302-5, with a fixed output voltage of 5.05V to 4.97V in high current mode.

How does it seem to make something out of nothing? With a few external components that are used to store electrical charge, and some internal oscillators. The chip can be sensitive to noisy input supply voltages, so there is a need for the capacitor C1 to be very close to the LT1302. Also, the diode must be a 2A schottky and not a regular one like a 1N4001, as they cannot react fast enough to the switching of the LT1302. The purpose of the oscillations is to allow the inductor to fill with current, and on the alternate oscillation cycle, it releases that current into a capacitor via the diode, and the voltage of this current is higher than the supply voltage. This is a very basic explanation, and more details can be found in the data sheet (link below).

But as always, it’s more interesting to do something than read about it – so we’ve constructed the demonstration circuit from the data sheet (below).

And here it is:

With an input supply voltage of 2 x 1.5V AA alkaline cells, our output voltage is 5.06V. This should be good for 600mA.

Finally, here is the very interesting and detailed data sheet: LT1302 data sheet. So there you have it! Another simple, useful and easy to implement part for you to use in your projects.

Thank you to Linear Technology for the samples of the LT1302 integrated circuits.

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#### John Boxall

Person. Founder and original author for tronixstuff.com. VK3FJBX

## 13 thoughts on “Part review – Linear Technology LT1302 DC/DC step-up converter”

1. Scott

Can this chip be made to boost 1 cell (or 2 NiMH cells) to say 3.6v?

I understand this IC is adjustable, but how to adjust it I could not grock from the data sheet.

1. John Boxall

Hello Scott
There is an example circuit on page 14 of the data sheet which boosts 1.5V to 5V, which could then be modified to your 3.6V. But it seems rather complex. Without knowing what space limitations your circuit has, I would most likely recommend going down from a regular 6V supply, or boosting 3V (2 cells) up to 5v (much simpler circuit, see adafruit mintyboost) then working with that.
Cheers
John

2. Scott

Thanks John.

I initially misread the specs, and believed this could output a range of voltages (vs the actual capability of 5V or 12V only). My error, but the data 1302’s data sheet has way too many examples which combine it with other LT chips..

So looking at this more, I could boost 2 to 3 NiMH to 5V with the 1302 (aka Minty) then slap a 3.6 voltage regulator on the output.

It seems a little wasteful to regulate, so I searched around and it looks like the Max757 can be “dialed” to anything between 2.7 to 5.5v. Nice!

One tradeoff of theMAX757 is it will only put out 1/2 the power of a LT1302 (300ma vs 600ma) but the 757 much cheaper also.

I -think- I have this correct, and I’m just answering my question for the sake of a Google search.

Basically the application(s) are similar to the Mintyboost: DIY battery pack(s) of varying voltage and capacity, that plug into Altoids tins which output a desired voltage and max power. Assuming one takes care to match battery packs to “altoid tins (voltage conversion)” to target device, you can produce a convenient suite of outputs for camping, etc. (Of course you could just run an inverter off a car battery, but where’s the fun in that?)

1. John Boxall

All good. You might want to put a heatsink of some sort on the MAX ICs, they can heat up after half an hour or so at full current.
have fun
John

1. Scott

Good idea. Will any old thermal adhesive work, or should certain types be avoided? I would be concerned about reactions between any compound and the plastic IC shell. I googled the issue, and came up mostly with people voicing the same concerns/uncertainty.

Sorry for the millionth question. 🙂

3. Ronald

Hi John,

Can I ask what kind of schottky diode you used in the circuit above? I have 1N5821, but it’s so big, it wouldnt fit on the breadboard. I’m looking for a replacement for it.

Ron

1. Jordan Whitley

I have used the 1n5819 before with it and it will work. I have also used the in5821 and used those Y-shaped stand offs that will allow you to put parts with big leads on proto board. I also have used the MBRS130 as specified in the datasheet and soldered leads onto it, and have gotten the best results using that part. It is very easy to do.

4. Jordan Whitley

I have been using the Linear LT1082 alot lately along with their LT1615 parts as well. They are insanely good parts!! Quesiton: do you know a way to increase the output current? Is it determined by the size of the inductor inbetween V-IN and the SW pins? In particular I am running the LT1615 boosting from 5v to 20v as an input into a PLC, I am currently outputting 12mA, and the PLC needs at least 9mA input to recognize this as a logic high signal. I am using a 10uH inductor right now, I would like to have a little bit more wiggle room than I currently have, would increasing the inductor to around 22uH help improve output current at all? Thanks a lot!

5. Muks

Hi there,

I am using this regulator on a bread board in pretty much the same way you are. I am however, not able to get a boosted voltage at the output. I put in 2.68v and get an output of 2.58v. I am using electrolytic capacitors for all of the capacitors though as I do not have ceramic ones. The output and input caps are both 100 micro farad. The inductor is 10micro henry. The diode is a 1N518 diode. The inductor and diode I obtained from the minty boost kit. And finally I am using a 10k resistor across the output. So I, was wondering what parts you were using and whether they were different from mine? Also was wondering if you encountered a similar problem to what I am facing and how you solved it?
Finally I see in the pics that you don’t connect pin 1 and 8 to ground. Is there a reason for this? Am I supposed yo do this? Just curious if I Have overlooked something in the data sheet regarding this.
Thanks
Muks

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