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Power Management ICs Forum Discussions

siz
Level 1
5 replies posted Welcome! First question asked
Level 1

Hello,

I have a doubt regarding the IRPS5401 tracking mode.

Looking at the UltraZED carrrier card  PS schematic, the LDO output is NOT connected to LDO_FB with resistor divider feedback:

Screenshot_2022-04-28_10-15-50.png

From what is seems, the IRPS5401's LDO is configured in NON tracking mode. This is what I understand also from the device evaluation kit user guide (https://www.infineon.com/dgdl/Infineon-UG-IRSP5401Demoboard-UM-v01_02-EN.pdf?fileId=5546d4625e37f35a...)

The guide says that:

Sink/Source (Tracking) mode
Set REG 0x1420 bit [8] (ldo_track_config) to 1
In Tracking mode, VO_LDO must be connected directly to FB_L.

Screenshot_2022-04-28_10-21-07.png

But when I look at the programmed register map from IR PowerIRCenter software (Read All Reg and the Save config file), it results that:

REG 1420h = 72FFh

where the 8th bit is set to 0, which would mean that the LDO is in non-tracking mode.

What am I misunderstanding about this configuration ?

Could someone clarify this ?

Thanks,

Simon

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1 Solution
SC
Moderator
Moderator 10 likes received 25 replies posted 10 solutions authored
Moderator

Hi,

The LDO has 2 modes, tracking, and non-tracking (source only)
It is not possible to have the LDO output 1.8V with FB_L open (or tied to GND)

Thanks,
SPCH

View solution in original post

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3 Replies
SC
Moderator
Moderator 10 likes received 25 replies posted 10 solutions authored
Moderator

Hi,

Thanks for posting at Infineon community.

I couldn't find the schematic at the UltraZED carrrier card.

As per the schematic snap shot what you shared, it says VO_LDO and FB_L pins are not connected with Resistive

divider as you said correctly.


At the same time VO_LDO and FB_L pins are not short, they are open. Hardware Configuration must be done to

select any of the mode (either short or keep divider).

 

Mode Selection Guide


1. Populate hardware divider between VO_LDO and FB_L pins for Non tracking mode and also Set REG 0x1420

bit[8] (ldo_track_config) to 0

2. Short between VO_LDO and FB_L pins for tracking mode and also Set REG 0x1420 bit [8] (ldo_track_config)

to 1.


Please let me know if need any help.

Thanks

SPCH

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siz
Level 1
5 replies posted Welcome! First question asked
Level 1

Hello @SC ,

The UltraZED IO Carrrier Card schematic can be found here:

https://www.avnet.com/opasdata/d120001/medias/docus/137/AES-ZU-IOCC-G-schematics.PDF

VO_LDO and LDO_FB ARE NOT shorted, sorry I made a typo, mistake and confusion in my first post.

In fact, R135 and R136 from schematics are not placed (DNP)

1651066161517.jpg

For what it seems from the configuration, the tracking mode is disabled, but the IRPS5401 datasheet says, at section 9.20:

The reference voltage for the LDO is nominally 0.5V and hence a resistor divider is needed from Vo_LDO to FB_L
to generate output voltages higher than 0.5V

So it's not clear to me how the 1V8 at the LDO output are generated.

The block schematic for the LDO is the following:

Screenshot_2022-04-28_15-52-43.png

Does the switch closed represent non tracking mode ?

With 1.8 V Delta V 15% on the non inverting input I could explain myself the 1V8 at the output (op amp connected as voltage follower).

Thanks

Simon

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SC
Moderator
Moderator 10 likes received 25 replies posted 10 solutions authored
Moderator

Hi,

The LDO has 2 modes, tracking, and non-tracking (source only)
It is not possible to have the LDO output 1.8V with FB_L open (or tied to GND)

Thanks,
SPCH

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