AM3517 Clock Specs

As mentioned in this other thread the clock specifications missing from the AM3517 datasheet is a known issue which should be rectified by the next revision of the document coming around the March time frame. In the mean time, the OMAP3 uses the same input clocking scheme, so you can take requirements from the OMAP3530 datasheet.

For the specific topic of voltage level on sys_xtalin and sys_xtalout, the datasheet does indicate the appropriate level of 1.8V.

Prad said:

What types of oscillator clocks are allowed? can I use 3.3V oscillator clock?

Table 2-1 indicates sys_xtalin and sys_xtalout use the VDDSOSC as the power for the I/Os.  This is 1.8V only, not 3.3V.

Hi,

Thankyou for the kind reply.

The AM3517 datasheet mentions that only 26MHz is allowed for Crystal oscillator clock or CMOS digital clock,
is there any technical reason behind this?
unlike AM3517,OMAP35x allows wide range of clock sources(12, 13, 16.8, 19.2, 26, or 38.4 MHz).

Regards.

in OMAP35xx we need 2 clock sources

1 - 32k clock

2 - system clock which can vary  (12, 13, 16.8, 19.2, 26, or 38.4 MHz).

in AM3517 in order to minimize system cost we woudl only need system_clk & 32k clock can be internally generated from system clock. 

As there is no spec for the system clock on AM3505 yet, we are forced to use the spec from the AM3530 in the interim.

Thi spec of +/- 1% pk-pk jitter and 3.6ns rise/fall time is actually quite hard to meet ?

a) are there suggested solutions for clk generation ( 26MHz ) which meet these specs cost effectively ?

b) can anyone suggest what the clock generation scheme is on the LogicPD AM3517 SoM ?

c) would the device(s) used in the OMAP3530 Beagleboard be OK / recommended for the AM3505 ? 

MikeWilliams said:

a) are there suggested solutions for clk generation ( 26MHz ) which meet these specs cost effectively ?

I don't know the cost, but the solution used on the LogicPD AM3517 SoM is an AP3S2-26.0MHz-ERBT oscillator.

MikeWilliams said:

b) can anyone suggest what the clock generation scheme is on the LogicPD AM3517 SoM ?

Personally, I would suggest that you sign up for access to the LogicPD technical documents for the TI based designs.  This way you can see what is used.

That said, I mentioned above how the 26MHz clock is delivered to the AM3517.  The 32.768KHz clock is a combination of a crystal and a SN74LVC1G125 to generate the single ended output.

MikeWilliams said:

c) would the device(s) used in the OMAP3530 Beagleboard be OK / recommended for the AM3505 ? 

The Beagleboard uses the TPS65950 PMIC that has circuitry integrated to generate the single ended clock inputs to the OMAP3530.  The TPS65950 PMIC has on the other side, the integrated oscillator circuit so that one uses a high frequency crystal and a 32.768KHz crystal.

You can also see this on the schematics for the Beagleboard.