SC4624A View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
SC4624A
Semtech Corporation
'SC4624A' PDF : 19 Pages View PDF
SC4624A
POWER MANAGEMENT
Application information (Cont.)
550kHz, the hiccup period is around 238ms. (refer to
Figure 7).
A poor layout will make OCP trip point shift and is not
easily to calculate by RISET. This is because it is affected
by ground bounce, spiker voltage between Vin pin and PH
pin, and internal parameter tolerance. Users can refer to
Figure 14, it shows how to set maximum output current
by RISET.
After the required inductor value is selected, the proper
selection of the core material is based on the peak
inductor current and efficiency requirements. The core
must be able to handle the peak inductor current IPEAK
without saturation and produce low core loss during the
high frequency operation and is given as follows:
,3($.
, , ,20$;
3 3
Vout A
B
The power loss for the inductor includes its core loss and
copper loss. If possible, the winding resistance should be
minimized to reduce any copper loss of the inductor, (the
core loss can be found in the manufacturer’s datasheet).
0
0.6 * Vout
Vo
C
The inductor’s copper loss can be estimated as follows:
3&223(5
, u 5
/506
:,1',1*
D
Iout
Imax
0
where
ILRMS is the RMS current in the inductor.
Figure 16. Over Current Protection Characteristic
This current can be calculated as follows:
Inductor Selection
For a typical SC4624A application, the inductor selection
is mainly based on its value, saturation current and DC
resistance. The inductor should be able to handle the
peak current without saturating and its copper resistance
in the winding should be as low as possible to minimize its
resistive power loss.
The inductor value can be determined according to its
operating point and the switching frequency as follows:
/
9 u 9 9 287
,1
287
9,1 u I6 u ', u ,20$;
,/506
,20$; u
u
',
Output Capacitor Selection
Basically there are two major factors to consider in select-
ing the type and quantity of the output capacitors. The
first one is the required ESR (Equivalent Series Resis-
tance) which should be low enough to reduce the voltage
deviation from its nominal one during its load changes.
The second one is the required capacitance, which should
be high enough to hold up the output voltage. Before the
SC4624A regulates the inductor current to a new value
during a load transient, the output capacitor delivers all
the additional current needed by the load.
where
fs = switching frequency.
DI = ratio of the peak to peak inductor current to the
maximum output load current.
The ESR and ESL of the output capacitor, the loop para-
sitic inductance between the output capacitor and the
load combined with inductor ripple current are all major
contributors to the output voltage ripple.
The peak to peak inductor current is:
, ', u , 3 3
20$;
2008 Semtech Corp.
Input Capacitor Selection
The input capacitor selection is based on its ripple cur-
rent level, required capacitance and voltage rating. This
capacitor must be able to provide the ripple current by the
13
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