Hi, I'm disty of Japan.
I have some question about TPS54821.
-- Back ground -------------------------------------------------------------------------------------------
Our important customer is evaluating TPS54821EVM now.
He asked me some question about the phenomenon that he found in the evaluation.
I confirm the phenomenon with a same condition as him and ask you some question about the evaluation result.
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I evaluated TPS54821EVM on following conditions.
1.Test conditions
C9、C10 ⇒ 100uF×3(changed value)
Model number：GRM32EB30J107ME16
L1：3.3μH
Model number：IHLP4040DZER3R3M01、DCR:13.7mΩ
R8 ⇒ 15kΩ(changed value)
R3 ⇒ 33kΩ(changed value)
R2 ⇒ open(changed value)
PVIN、VIN：shorted
Iout：3.2A(constant：added 0.31Ω VOUT to GND)
Temp：room tmp
Fsw:1.4MHz(design value)
VIN:5 to 11V
VOUT：1V(design Value)
measurement point：PH(TP7)、VOUT(TP9)、VIN(TP1)、IOUT(current probe)
2.Result
①When VIN was 5V,high pulse width of ph was about 160ns.
There is no problem in particular on all waveforms.
(see the attached file)
②When VIN was 5.5V,Jitter appeared on the high pulse width on PH signal.
The high pulse width was about 120 to 180 but Fsw was constant(1.4MHz).
And the waveform of VOUT voltage does not seem to have any problem.
(see the attached file)
③When VIN was 9V,the high pulse omission on PH signal occurred and Fsw was not
1.4MHz. And the minimum high pulse width on PH signal was about 100ns.
(see the attached file)
④When VIN was 11V、the high pulse omission on PH signal occurred more.
(Fsw was not 1.4MHz)
And the minimum high pulse width on PH signal was about 100ns.
(see the attached file)
③,④ Result waveform：
The output voltage appears to be fluctuates, by frequency is changed.
3.Questions
①Does the jitter that appeared at "VIN = 5.5V" usually occur?
Does the jitter affect VOUT?(ex. a ripple voltage increase)
Is there any problem,if we use TPS54821 in this conditions?
②Is the jitter related with a value of C11?(C11＝470pF:current condition)
③Does the phenomenon of pulse omission that appeared at "VIN = 9V" usually occur?
Does the pulse omission affect VOUT ?(ex. a ripple voltage increase)
Is there any problem,if we use TPS54821 in this conditions?
④I think that the high pulse width of 100ns(when VIN is 9V) is "minimum on time" of this sample
on this EVM.
Is it correct?
⑤Does it affect VOUT that a voltage of 11V(more than 9V) apply VIN,If "minimum on time" of
this sample is 100ns(VIN=9V)?
Is it thought that the voltage of VOUT greatly changes?(ex. the VOUT voltage decrease or increase)
Is there any problem,if we use TPS54821 in this conditions(VIN＝11V)?
I would appreciate if you lend your expertise to me.
Best regards.
