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transient response performance DCDC vs LDO

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rock_zhu

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Hello everybody
why dcdc's transient reponse speed is lower than LDO's normally?Thx
 

rock_zhu said:
Hello everybody
why dcdc's transient reponse speed is lower than LDO's normally?Thx
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LDO has no clock signal, DCDC has clock signal.
 

we know that LDO' transient reponse performance has relation with closed loop bandwidth and Cload. what about DC-DC?
 

Can anyone please throw some more light on this topic.
 

Generally you want your loop bandwidth to be 1/10
your switching frequency or lower. This sets a limit.
Now, my DC-DC designs can switch up to 5MHz and
maybe 500kHz loop BW isn't the same kind of problem
that you'd have with a 100kHz chop, 10kHz BW old
school switcher.

A DC-DC has the advantage that its output impedance
is constantly low, and Cload is usually just a bonus.
An LDO at low current has a high output impedance,
at high current near dropout a low impedance, and
making a loop that's happy for all cases means a
fairly fussy components selection for output filter
(or a really soggy loop and poor load step response).
 

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