LSF0108: Vref_B can't reach 3.3V?

user4979899

Expert 3080 points

Part Number: LSF0108

Hi Sir,

Below is my customer's design and they measurement

Pin 19 = 2.012 V
Pin 2 = 1.193 V

Can we adjust R196 resistor value to make the Pin19 to move to 3.3V?

Thanks

over 5 years ago

0 Dylan Hubbard over 5 years ago

TI__Mastermind 46025 points

Hi Anne,

No the 200kohm is necessary to bias the LSF correctly. Please see the training videos below for more clarity:

https://training.ti.com/tlm-lsf-bias?context=1134826-1139264-1134790

0 user4979899 over 5 years ago in reply to Dylan Hubbard

TI__Expert 3080 points

Do you have any idea why pin19 is 2.012V only?

0 Clemens Ladisch over 5 years ago in reply to user4979899

Guru 317350 points

Because this is how the LSF works. See the application report Voltage-Level Translation With the LSF Family (SLVA675):

Connecting the EN pin directly to Vref_B ensures that the voltage drop over the reference transistor's source/drain channel is the same as its threshold voltage.

Logic

Logic forum

LSF0108: Vref_B can't reach 3.3V?