LSF0108: REF_A input is acting as a current source

Cscott

Intellectual 310 points

Part Number: LSF0108

Situation:

REF_A= 3.3V;

REF_B = 5V Via 1K resistor to limit current during testing,

EN= +5V via 200K,

Pin 1 = GND,

A pins=open,

B pins +5V via 10k

I am finding that the Ref-A input is acting as a current source when VRef_A - VRef_B > 1.2V. I have replaced the chip, checked the pinout and lifted the Ref_A pin2 to confirm that it is the current source. I would have expected only leakage currents on the ref pins.

Any suggestions?

-CS

over 8 years ago

0 Emrys Maier over 8 years ago

TI__Guru* 97046 points

Hi CS,

You need to tie Vref_B and EN together, then connect them through the 200kohm resistor to the 5V supply. Please see Figure 1 in our application note Voltage-Level Translation With the LSF Family.

0 Cscott over 8 years ago in reply to Emrys Maier

Intellectual 310 points

HI Emrys,

I expect that is the issue. As that connection is shown in every diagram I'm wondering how I managed to overlook it. I'll try that out asap.

Thanks.

Logic

Logic forum

LSF0108: REF_A input is acting as a current source