SC4524CSETRT View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
SC4524CSETRT Datasheet PDF : 22 Pages
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SC4524C
Applications Information (Cont.)
D1
BST
VIN
SC4524C
IN
SW
C1
3V < VO < 8V
GND
D2
Substituting the first equation into the second equation,
G9R ,66
GW &66
where VSS is the soft-start capacitor voltage and ISS is the
soft-start charging current. V1 is the voltage defined in
Figure 2.
(a)
D3 D1
BST
C1
VIN
SC4524C
IN
SW
GND
D2
VO < 2.5V
(b)
D1
BST
VIN
SC4524C
IN
SW
C1
2.5V < VO < 3V
or VO > 8V
D2
GND
(C)
Figures 6 — Methods of Bootstrapping the SC4524C
Minimum Soft-start Capacitance CSS
To ensure normal operation, the minimum soft-start
capacitance CSS can be calculated in terms of the output
capacitance CO and output load current IO according to
the following equations.
G9 66
GW
G9 2
GW
,66
&66
G9
GW
G
GW
> 966
9 @
To ensure successful startup, the total current drawn
from the output must be less than the maximum output
capability of the part,
92
5
&2
u
G9 2
GW
d
$
Substituting the third equation of this section into the
previous equation,
92
5
,66
u
&2
&66
d
$
Rearranging,
&66 t
,66 0$; u&2
$
¨¨©§
92
5
¸¸¹·
Therefore the minimum CSS depends on the output
capacitance and the load current. Larger CSS is necessary
when starting into a heavy load (small R).
13
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