AM5728 SYSCLK sequencing requirement

Shareef

Expert 1985 points

Other Parts Discussed in Thread: AM5728

Hi All,

This post is regarding the SYSCLK inputs to AM5728 device when external clock oscillators are used.

1. From the AM5728 Datasheet Figure 5-1 Power ON Sequence, xi_osc0 clocks are getting enabled only after the last power supply vddshv8/vdda33v_usb. Is this a mandatory requirement to be followed for external oscillators (XO)? In other words, can XO start driving clock as input to AM5728 pins as soon as its Vcc (1.8V) which comes earliest in power on sequence is available?

2. The xi_osc0 and xi_osc1 pins are powered by VDDA_OSC domain. Is it necessary that the external XO be supplied by the same 1.8V which is being supplied to the VDDA_OSC pins of the processor?

3. In the case of RTC_OSC_XI_CLKIN32 pin, this pin is being powered by the VDDA_RTC domain. I believe since AM5728 does not support RTC only mode, the RTC XO can be supplied by VDDS18V supply itself. Please confirm.

Regards,
Shareef

over 7 years ago

0 Biser Gatchev-XID over 7 years ago

TI__Guru**** 393215 points

Hi,

1. Section 6.1.2.2 from the AM572x Datasheet applies.
2. Yes. This also answers when the clock should start, from your first question.
3. See processors.wiki.ti.com/.../AM572x_Schematic_Checklist

0 Shareef over 7 years ago in reply to Biser Gatchev-XID

Expert 1985 points

Hi Biser,

Thanks. Please see my response inline to yours.

1. Section 6.1.2.2 from the AM572x Datasheet applies.
- provides clock specifications but does not talk about sequencing of the oscillator. Generally oscillators have max start up time defined to be in the range of 3ms to 5ms. Hence I am being over cautious to not violate the specs. Can you elaborate more on this?

2. In my design, I have powered xi_osc0 and xi_osc1 from D1V8 (VDDS18V) supply which ramps up first in the PMIC just before VDDA_OSC. Is this fine?

3. Fine, I understand that RTC XO can be powered by VDDS18V supply.

Thanks,
Shareef

0 Biser Gatchev-XID over 7 years ago in reply to Shareef

TI__Guru**** 393215 points

the 1.8V supply for the VDDA_OSC processor power pins should be taken from the LDOLN_OUT output of the PMIC. The same supply should be used for the external oscillator. This should resolve all your concerns.

Processors

Processors forum

AM5728 SYSCLK sequencing requirement