TPS61251: 340uA in snooze Mode

Hi Thang,

I don't understand your meaning. Where is R1 in schematic? 

'When the LTE module is in power save, the current draw is about 7.5uA. The circuit works fine, but when I put the LTE modul in powersave mode, it draws 340uA from the battery.' I'm confused what's the load current in power save mode because here you said power save mode twice.

Hi Zack Liu,

I mean R1 in figure 6 in datasheet, but in my schematic it is R13//R14.

1. LTE module in power save mode without TPS61251: 7,5 uA 

2. LTE module in power save with TPS61251: 340uA

BR

TDD

Hi Thang,

TPS61251 is a boost converter which means the output voltage is stepped up from input voltage. When battery voltage is in the range of 2.5V to 3.3V, output voltage could keeps at 3.3V. However, when battery voltage is in the range of 3.3V to 6.0V, TPS61251 works at 100% duty-cycle mode. When means the output voltage follows the input voltage and will not fall below the programmed value. Vout is higher than 3.3V in this range. Could the LTE module accept it?

Thanks for explaining the two conditions difference. That's clear to me now. I'll do a bench test with EVM and let you know the result once it's done.

Hi Thang,

I test the EVM with a 7uA load current but cannot see 340uA current drawn from battery.

Can you measure SW, Vout pin waveform with oscilloscope?

Hi Zack Liu,

Yes, the LTE module will accept it. The LTE module have VDD, max = 5.5V and VDDIO, max = 3.9V.

BR

TDD 

Hi Zack Liu,

Please find attached the waveform if Vout and SW.

Yellow = Vout

Blue = SW

What is the quiescent current in 100% duty-cycle mode when battery voltage is in the range of 3.3V to 6.0V?

BR

TDD

Hi Thang Do,

Please make sure the LTE module is not periodically waked up which could prevent TPS61251 to enter snooze mode. I would visualize the output current of the regulator to see if there is no fluctuations. 

Regards,

Abdu

Hi Abdu,

I'm sure the LTE module is in power save mode. The LTE module will wake up from power save mode in every hour.

When I changed the input capacitors C14 and C15 to larger values (C14=C15=22uF), I see 45uA current drawn from battery.

BR

TDD

Hi Thang,

The waveform you shared cannot tell me the switching frequency of SW pin. Can you change the time scale of oscilloscope and read the period of switching? It's important because it could tell me if the 340uA is due to the switching. Probe the Vin pin at the same time to see if there is any ringing.

And please also share the layout. 

Hi Zack,

New wavform.

PCB Layout:

L1: Tantal capacitor place on the top_layer

L2: GND

L3: Power

L4: Bottom layer, TPS61251

BR

TDD

Hi Thang,

When you do this test to measure input current, what's the input voltage? Is it higher than the programmed Vout 3.3V?

In that case, the device will draw more current than 2uA. If you decrease input voltage less than 3.3V, the average input current should be around 2uA.

Hi Zack Liu,

The input voltage is 3.57V. 

Yes, the input voltage is higher than the programmed output voltage (3.34V).

BR 

TDD

Hi Zack Liu,

Yes, we can accept that. :-)

Thx.

BR

TDD