A6985F datasheet(55/77 Pages) STMICROELECTRONICS

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A6985F

Application notes

For example with VOUT = 3.3 V, VIN = 12 V, IL = 0.25 A, fSW = 2 MHz (resulting by the

inductor value) and COUT = 10 F MLCC:

Equation 54

The output capacitor value has a key role to sustain the output voltage during a steep load

transient. When the load transient slew rate exceeds the system bandwidth, the output

capacitor provides the current to the load. In case the final application specifies high slew

rate load transient, the system bandwidth must be maximized and the output capacitor has

to sustain the output voltage for time response shorter than the loop response time.

In Table 15 some capacitor series are listed.

Table 15. Output capacitors

Manufacturer

Series

Cap value (

F)

Rated voltage (V)

ESR (m

)

MURATA

GRM32

22 to 100

6.3 to 25

< 5

GRM31

10 to 47

6.3 to 25

< 5

PANASONIC

ECJ

10 to 22

6.3

< 5

EEFCD

10 to 68

6.3

15 to 55

SANYO

TPA/B/C

100 to 470

4 to 16

40 to 80

TDK

C3225

22 to 100

6.3

< 5

V

OUT

VOUT

------------------

VOUT

--------------

I

LMAX

COUT fSW



------------------------------





3.3

--------

0·25

810

F2MHz



----------------------------------------------









1·6mV

3.3

-------------------

0.05%

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