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Power Supply of DS90C363B

g.f.
Guru 15510 points
Other Parts Discussed in Thread: DS90C363B

Hi,

I have question about DS90C363B power supply.

Q1.
DS90C363B has three power supply pins(Vcc, PLL Vcc, LVDS Vcc).

In customer board, it is generating 3.3V for LCD and 3.3V for other logics separately.
Above Vcc, PLL Vcc pins are supplied from same power source(3.3V for other logics)
and LVDS Vcc pin are supplied from different power source(3.3V for LCD).

But in datasheet of DS90C363B page.9, it said as follow:
*********************************************************************************
it is recommended to have VCC, LVDS VCC and PLL VCC from the same power source with
three separate de-coupling bypass capacitor groups.
*********************************************************************************

Is there any problem if supplying from different power source?

Q2.
As same power source are recommended, I guess the power entering to
each Vcc, PLL Vcc, and LVDS Vcc will be almost same timing.
But in our board, 3.3V for logics goes up first and then 3.3V for LCD goes up.
So, the 3.3V power enters LVDS Vcc first and then Vcc, PLL Vcc which are not simultaneously.
Does power must enter LVDS Vcc, Vcc, PLL Vcc simultaneously?

In data sheet page.9, it said as follow:
****************************************************************
There is no requirement on which VCC entering the device first.
****************************************************************
So, I guess it doesn't need to be simultaneously. Is it correct?

best regards,
g.f.

  • 0
    TI__Mastermind 29655 points
    Hi g.f.,

    Please see answers to questions below:

    1. I think in most cases it is okay if 3.3 V is supplied by a different power source. My only concern would be whether the power sources share the same GND. If not, I would beware of any shifts in the ground reference if, say, the power sources are coming from two different boards.

    2. This device does not require a specific power-up sequence for the VCC. However, if you expect there to be some delay in the 3.3 V coming from the logics power supply versus the 3.3 V coming from the LCD, I would recommend that you hold the /Power Down pin Low until the LVDS VCC is asserted. This assures that all power supplies are provided when the DS90C363B begins receiving active data.

    Thanks,

    Michael