EL7554IREZT13 INTERSIL [Intersil Corporation], EL7554IREZT13 Datasheet - Page 11

• Manufacturer Part Number: EL7554IREZT13
• Description: Monolithic 4 Amp DC-DC Step-Down Regulator
• Manufacturer: INTERSIL [Intersil Corporation]

Figure 18 shows the waveforms.
In this application, C
reduce input/output ripple because the pulse skipping nature
of the method.
2. CASCADE START-UP
In this configuration, EN pin of Regulator 2 is connected to
the PG pin of Regulator 1 (Figure 22). V
after V
3. LINEAR START-UP
In the linear start-up tracking configuration, the regulator with
lower output voltage, V
voltage, V
4. OFFSET START-UP
Compared with the cascade start-up, this configuration
allows Regulator 2 to begin the start-up process when V
reaches a particular value of V
V
V
O2
O
V
O2
O1
FIGURE 23. LINEAR START-UP TRACKING
is good.
O1
FIGURE 21. ADJUSTABLE START-UP
. The waveform is shown in Figure 19.
FIGURE 22. CASCADE START-UP
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+
-
IN
+
-
EN
O2
and C
STN
STP
, tracks the one with higher output
V
V
O1
IN
V
O1
11
OUT
R
200K
REF
C
V
IN
may be increased to
*(1+R
0.1µF
V
V
O1
O2
V
V
O2
O1
O2
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B
/R
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will only start
A
+
T
) before PG
-
ST
PG
STN
STP
V
R
O1
IN
C
V
V
IN
O
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goes HI, where V
V
Component Selection
INPUT CAPACITOR
The main functions of the input capacitor(s) are to maintain
the input voltage steady and to filter out the pulse current
passing through the upper switch. The root-mean-square
value of this current is:
for a wide range of V
For long-term reliability, the input capacitor or combination of
capacitors must have the current rating higher than I
Use X5R or X7R type ceramic capacitors, or SPCAP or
POSCAP types of Polymer capacitors for their high current
handling capability.
INDUCTOR
The NFET positive current limit is set at about 0.5A. For
optimal operation, the peak-to-peak inductor current ripple
∆I
inductance value:
The peak current the inductor sees is:
When inductor is chosen, make sure the inductor can handle
this peak current and the average current of I
OUTPUT CAPACITOR
If there is no holding time requirement for output; output
voltage ripple and transient response are the main deciding
factors in choosing the output capacitor. Initially, choose the
V
I
I
L
LPK
IN,RMS
REF
O2
L
=
should be less than 1A. The following equation gives the
(
------------------------------------------- -
=1.26.
V
=
V
IN
IN
I
O
=
FIGURE 24. OFFSET START-UP TRACKING
–
×
+
-----------------------------------------------
V
∆I
∆I
--------
V
V
O
2
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L
REF
O
L
)
×
×
×
F
V
(
V
REF
S
V
+
-
O
IN
IN
IN
–
is the regulator reference voltage.
V
V
and V
IN
O
)
×
V
R
REF
I
O
O
A
.
≈
R
(1+R
V
1/2
B
O1
B
I (
/R
V
V
O
A
O1
O2
)
)
O
.
EL7554
January 31, 2005
IN,RMS
FN7360.2
V
IN
.