I am using LCD with below power interface.

Power requirement

But as per below note in LCD datasheet, VCC and VGL need to apply first and then VGH. My query is why such power sequencing is needed ? power requirement
If I use below circuit for power, is it enough for power requirement of TFT? schematic 1

schematic 2 LCD Connection: LCD Connection

  • 1
    \$\begingroup\$ Please indicate on the diagram where this circuit interfaces to your LCD voltage supply pins - I don't see Vgh's supply. \$\endgroup\$
    – Andy aka
    Jan 6, 2016 at 12:54
  • \$\begingroup\$ And once it's in there I'm going to be betting that, no it isn't sufficient. Supply sequencing is to prevent internal feed-throughs of power through translatory stages between drive levels, in most cases, this feed-through can damage or latch circuits. Which means you need to be 100% sure, because anything else is going to be 0% reliable. \$\endgroup\$
    – Asmyldof
    Jan 6, 2016 at 14:37
  • \$\begingroup\$ @Andy aka,U3 is used for generating VGH,VGL, AVDD voltages...VGH=16V, VGL=-7V, AVDD=10.4V; LED+ & LED- are back-light pins generated using U4, VCOM is generated using voltage divider on 5V supply... +5V and +5V_A are same pins used as input to boost conv U3 and U4 , VCC=3.3V is generated using LM1117-3.3V (not shown here) \$\endgroup\$ Jan 6, 2016 at 15:59
  • \$\begingroup\$ Please see edited question.. LCD connector added. \$\endgroup\$ Jan 6, 2016 at 16:13

1 Answer 1

why such power sequencing is needed ?

Because the datasheet says so.

Seriously, this is actually the only relevant answer. It's not your business to second-guess the datasheet. If it says you need to do something to make the device work, then you need to do that if you want the device to work. Guessing why the manufacturer says something is necessary, then not completely following the requirements because you think you know better is irresponsible design.

One possible reason is that there may be a latchup problem. If power is brought up in the wrong sequence, then maybe some parasitic SCR or something gets turned on, a lot of current is drawn when the remaining supplies are brought up, the poof.

However, again, it's not your business, other than just curiosity, why a spec is what it is. It's a spec, a rule. Follow it or else. If it's too inconvenient, then find a different part that doesn't have such a requirement.


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