Micro watt range boost converter design

[Wanoz]

I want to design a boost converter which operates input 100mV and steps up to 1.5V with 0.13um cmos technology. Assume, I have 0.6 to 1V external voltage source to power up control circuit. What are the crucial stuffs in design should be considered and how to deal with them?
Attached the circuit diagram. How to obtain power efficiency graph vs. output power or output current.
Any help will be appreciated.

 

[Wanoz]

Calculate boost converter output power

When calculate boost converter output power, is it considered the output capacitor power? What kinds of equations can be used to determine the boost converter output power?

 

[BradtheRad]

Re: Calculate boost converter output power

When calculate boost converter output power, is it considered the output capacitor power?

The output capacitor has pulses of current going back and forth through it, often several Amperes. These tend to be greater as you draw greater power.

What kinds of equations can be used to determine the boost converter output power?

The simple way to calculate output power: (a) measure voltage at the load, (b) multiply by Amperes through the load (average).

Output power is related to input power, since Watts in is roughly equal to Watts out. Naturally you need to take parasitic losses into account.

 

[dick_freebird]

Your most crucial problem is that 100mV will not turn on
any "regular VT" device, and any "native" (VT ~ 0) device
will not turn off full (so very wasteful of input power).

To run a decent boost backend you would need to ring
up a supply nearly as large as what you hope to create,
just for gate drive. That alone will probably consume
all or most of your microwatts.

You should look at what people are doing & have done
in RFID tags, which have similar (or maybe identical)
challenges.

 

[Wanoz]

Re: Calculate boost converter output power

multiply by Amperes through the load (average).

How to calculate the average output current?

 

[d123]

Hi,
Basic way is: V out/R load

If V out operates at a duty cycle, you could multiply V out/R load calculation by duty cycle: (5V/50R) * 0.45D. Or with a current probe seeing Iout max and I out min and dividing by 2: 1A + 0.5A/2 = 0.75A.

 

[BradtheRad]

Re: Calculate boost converter output power

How to calculate the average output current?

If you mean calculate rather than measure, it's a bit of work. A burst of current from the inductor adds voltage on the output capacitor. There's a formula for this although it must be complicated, since I don't remember how it goes.

Output voltage rises until equal energy is subtracted by the load as is added by the inductor. Again the formula becomes complicated.

If you wish to deliver a particular wattage to the load, you must supply power through the inductor for a sufficient time, so that current builds to a sufficient level. Energy stored in the inductor can be measured in Webers (L x A), as an easy unit to use in conversion forumulae.

 

[dick_freebird]

I think you may want to look at transformer styles
and not just the classical boost (inductor) type.
Boost efficiency suffers badly at high ratios of
VOUT/VIN. To operate at such low voltage you
also will likely oversize your FET and its added C
steals from inductor current delivery at turnoff.
If you make your voltage gain using windings
ratio you may be able to use a smaller switch
device. However this all depends on what you
are constrained to by cost, volume and other
sides of the "box".