參數(shù)資料
型號： MAX624
廠商： Maxim Integrated Products, Inc.
英文描述： Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications(升壓型，輸出電壓5V/12V/可調,輸出電流200mA的DC-DC變換器)
中文描述： 雙輸出，1MHz的DC - DC升壓轉換器應用為PCMCIA（升壓型，輸出電壓5V/12V /可調，輸出電流200毫安的直流變換器）
文件頁數(shù)： 12/16頁
文件大?。?/td> 215K
代理商： MAX624
M
To select the inductor value for the main SMPS, take
the following steps:
1) Select the input voltage.
2) Select I
LIMIT
and I
LOAD
.
3) Use the specified data sheet values and the following
formula:
SR5 x K5 (V
- A)
L (in H) = ———————————————
2 x I
LIMIT
(V
IN
+ A) - 2 x I
LOAD
x B
A = I
LIMIT
x R
ON
B = V
OUT
+ V
DIODE
where: inductor current = I
LIMIT
(min) = 0.7A,
I
LOAD
(min) = 200mA, SR5 (the switch off-time ratio) =
0.8, K5(max) = 1.7μs-V, R
ON
(max) = 0.6
, V
OUT
=
5V, V
DIODE
= 0.5V, V
IN
(min) = 3.0V, and L = 5μH (for
best performance, use a Sumida 5μH (CLS-62B)).
Input Filter Capac itor S elec tion
The input filter capacitor is required to reduce reflected
current ripple to the input source, and to improve effi-
ciency by providing a low-impedance path for the rip-
ple current. For memory card applications, the input
filter capacitor is absolutely necessary due to possible
contact resistance in the edge connector. To limit surge
currents, use smaller values. Ceramic capacitors are
the best choice.
Output V oltage and Component
S elec tion for the Auxiliary S MPS
To select the output voltage and component values for
the auxiliary SMPS, take the following steps:
1) Select the desired output voltage between 5V and
15V (e.g., 12V).
2) Select the minimum input voltage (V
IN
).
3) Select R6 and R5. Choose R6 in the 10k
to 200k
range (e.g., 100k
). Choose R5 = R6 (V
OUT
/ V
REF
-
1). For example, if V
OUT
= 12V, then R6 = 100k
and
R5 = 500k
.
4) Select the desired output current (I
OUT
). Calculate
the minimum inductor current (I
LIMIT
) using the fol-
lowing formula:
I
LIMIT
(in Amps) = [(V
OUT
+ 0.5V) / (V
IN
(min) - 0.3V)]
x I
LOAD
x 2
For example: V
OUT
= 12V, V
IN
(min) = 3V,I
LOAD
=
80mA, and I
LIMIT
= 0.7A.
5) To calculate the minimum required inductor value,
use the following formula:
SRA x KA (V
- A)
2 x I
LIMIT
(V
IN
- A) - 2 x I
LOAD
x B
L (in H) = ——————————————
A = I
LIMIT
x R
ON
B = V
OUT
+ V
DIODE
For example: I
LOAD
= 80mA, I
LIMIT
= 0.7A (calculat-
ed using the above formula), SRA (switch off-time
ratio) = 0.9, KA (switch on-time) = 3.0μs-V,
R
ON
(max) = 0.2
, V
OUT
= 12V, V
DIODE
= 0.5V, and
L(min) = 3.8μH.
6) R (in
) = 180mV / I
LIMIT
= 0.25
for I
LIMIT
= 0.7A.
7) To select the output capacitor value, take the follow-
ing steps:
A) Select the maximum ripple you can tolerate.
B) Calculate C
F
using the formula below.
LOAD
V
RIPPLE
C x (V
OUT
+ 0.5 - V
IN
)
C
F
(in F) = ——2 x KA x I
C) Calculate the output capacitor’s required ESR
using the formula below.
RIPPLE
ESR x V
IN
4 x I
LOAD
x (V
OUT
+ 0.5V - V
IN
)
ESR (in
) = ——V
___PC Board Layout and Grounding
Because of the MAX624’s high-frequency operation,
careful PC board layout is necessary to minimize
ground bounce and noise. PC board layout instructions
should be explicit, and the layout artist should work
from a pencil sketch that shows the placement of
power switching components and high-current routing.
Use Figures 3–8 (the component placement guide and
PC board layouts for the MAX624 evaluation board) as
a rough guide for component placement and ground
connections. A ground plane is essential for optimum
performance. In most applications, the circuit will be
located on a multilayer board, and full use of the four or
more copper layers is recommended. Use the following
step-by-step guide.
1) Place the high-power components (C1, C2, C3, D1,
D2, L1, L2, Q1, and R1) first.
Priority 1: Minimize current-sense resistor trace
lengths.
Priority 2: Minimize ground trace lengths in the high-
current paths (the bold lines in the appli-
cation circuits).
Priority 3: Minimize other trace lengths in the high-cur-
rent paths. Use traces more than 5mm wide.
Ideally, surface-mount power components are
butted up against one another with their ground ter-
minals almost touching. These high-current grounds
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applic ations
12
______________________________________________________________________________________
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