LMR36520: how to test the Operating quiescent current?

Stanley Xu

Part Number: LMR36520

Hi engineers, I'm studying buck circuit through LMR36520 recently, I want to know the power consumption of LMR36520 when no load is connected, so I pay attention to the IQ parameter in datasheet, as show in picture.

Note 2 explain that "This is the current used by the device open loop. It does not represent the total input current of the system when in regulation"

I wonder：

how to test the Operating quiescent current of LMR36520?

what are the test conditions?

what‘s the “non-switching” means？

can IQ-nonSW be used to calculator the power consumption of LMR36520 when no load is connected？

My understanding about the key test conditions is that ：

1.device enabled.

2.FB PIN floating, the device open loop, so as an actuator in the feedback loop the MOSFET does not switch.

3.Vout floating.

I‘m looking forward for your answer and advice, thank you！

over 4 years ago

+1 Andy Chen over 4 years ago

TI__Mastermind 34875 points

Hi Stanley,

IQ-nonSW tested as below:

1. .device enabled.

2. bias FB PIN to Vref x110% voltage.

To check the standby current at no load:

1.device enabled.

2. Output open (do not connect to any E-load)

3. Use as larger as possible feedback resistor..

B R

Andy

0 Stanley Xu over 4 years ago in reply to Andy Chen

TI__Intellectual 1830 points

thank you for your kindly answer, by the way, what‘s the “non-switching” means？

+1 Andy Chen over 4 years ago in reply to Stanley Xu

TI__Mastermind 34875 points

Hi Stanley,

If the output is biased little higher than target output value, then the circuit will stop switching all the time till the Vout drop to nominal value, this mean the Non-Switching state.

B R
Andy

0 Stanley Xu over 4 years ago in reply to Andy Chen

TI__Intellectual 1830 points

my understanding is show as below picture, FB bias to 1.1V(110% of Vref), at this time buck stop switching but other circuit contained in the component such as control logic, Vref, LDO and so on, still running, so the IQ-nonSW represent to the quiescent power consumption contributed by the circuit other than BUCK, right? why set feedback resistor as larger as possible?

+1 Andy Chen over 4 years ago in reply to Stanley Xu

TI__Mastermind 34875 points

Hi Stanley,

For some converters with extreme lower Iq, some inside circuit cell also shutdown to reduce quiescent current.

The larger feedback resistor will reduce dead load current to improve efficiency at light load condition.

B R

Andy

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LMR36520: how to test the Operating quiescent current?