The TPS78233 is probably industry’s LDO with the lowest quiescent current. While working on a boosterpack for TI’s Launchpad I took the chance to measure actual current consumption of this LDO, as well of the voltage supervisor: ON semi’s NCP301LSN30T1.
The TPS78233 promises a typical no-load quiescent current of 420nA. Current into the EN pin is tipically 40nA at 5.5V. This yelds a pretty impressive figure of 470nA typical supply current.
I am working on a small board that uses this chip, so I decided to give it a test and check if it lives up to its expectations. This prototype includes the TPS78233 from Texas Instruments and the NCP301LSN30T1 from ON Semiconductor. Both devices promise extremely low supply current, which is precisely what I am looking for. For this test I used a Lithium Ion battery. The battery’s voltage was measured and registered 3,84V.
My multimeter can’t go below 1uA or 100uV, which is still high (!!!), compared to the current that I’m trying to measure. So, in order to measure currents as low as few nA, I decided to mount a current sense resistor with 10kOhm. This yelds 10mV at 1uA, which isn’t much.
Now we are all set to make a few measurements and check how low is the supply current and power dissipation of this little device.
The first measurement was made with the switch the EN pin tied low, ie, with the regulator disabled.
0,3mV through a 10kOhm resistor give 30nA of current. Quite impressive, although not as low as the 18nA referenced in the datasheet. Still, this board wasn’t clean at all, there were still flux residues and even breath caused this value to oscillate. For very short moments, the multimeter showed 0,2mV, so the actual value is probably somewhere in between 0,2mV and 0,3mV.
Now let’s see what happens when we activate the TPS78233…
450nA quiescent current! It turns out the TPS78233 really meets the expectations! I’m impressed! With a supply voltage of 3.84V this LDO’s power consumption is only 1,73uW. Wow…
So, the next step is to add the voltage supervisor into the mix and see the effect it produces on overall power consumption.
The voltage supervisor mounted on the board:
Now, we’ll repeat our measurements. First, supply current with the voltage regulator disabled.
Current sense voltage is now 2.2mV. This means that supply current is 220nA. The voltage supervisor added 190nA to the circuit’s supply voltage. Measuring the supply voltage and protecting the battery against over-discharge with 190nA is more than a fair price to pay.
The supply current of the NCP301LSN30T1 shouldn’t depend on the ON/OFF state of the TPS78233 LDO. We’re just about to confirm that…
Turning the regulator ON gives a not susprising 6,4mV, which means supply current is now 640nA. This was already expected: an increase of 190nA in the supply current of the whole circuit.
One might think that the TPS78233 seems to good to be true, after reading the datasheet. However, this test shows that the TPS78233 really does deliver the performance it promises.
The voltage supervisor is also a remarkable device in terms of running with a residual supply current.
Summary of supply current per device:
|POWER SWITCH POSITION|
- Product page of the TPS78233: http://www.ti.com/product/tps78233
- Product page of the NCP301LSN30: http://www.onsemi.com/PowerSolutions/product.do?id=NCP301
- Texas Instruments’s Launchpad: http://www.ti.com/launchpad