參數(shù)資料
型號: MAX1778EUG
廠商: MAXIM INTEGRATED PRODUCTS INC
元件分類: 穩(wěn)壓器
英文描述: Quad-Output TFT LCD DC-DC Converters with Buffer
中文描述: 2.05 A SWITCHING REGULATOR, 1250 kHz SWITCHING FREQ-MAX, PDSO24
封裝: 4.40 MM, 1.10 MM HEIGHT, MO-153AD, TSSOP-24
文件頁數(shù): 27/38頁
文件大?。?/td> 1051K
代理商: MAX1778EUG
M
Quad-Output TFT LCD DC-DC
Converters with Buffer
______________________________________________________________________________________
27
Rectifier Diode
Use a Schottky diode with an average current rating
equal to or greater than the peak inductor current, and
a voltage rating at least 1.5 times the main output volt-
age (V
MAIN
).
Charge Pumps (MAX1778/ MAX1880/
MAX1881/MAX1882 Only)
Selecting the Number of Charge-Pump Stages
The number of charge-pump stages required to regu-
late the output voltage depends on the supply voltage,
output voltage, load current, switching frequency, the
diode
s forward voltage drop, and ceramic capacitor
values.
For positive charge-pump outputs, the number of
required stages may be determined by:
where V
SUPD
is the positive charge-pump diode supply
(Figure 4), V
DIODE
is the diode
s forward voltage drop,
and R
TX
is the charge pump
s output impedance. The
charge pump
s output impedance may be approximat-
ed using the following equation:
where the charge pump
s switching frequency (f
CHP
) is
equal to 0.5 x f
OSC
, the P-channel MOSFET
s on-resis-
tance (R
PCH(ON)
) is 10
, and the N-channel MOSFET
s
on-resistance (R
NCH(ON
)) is 4
(see
Electrical
Characteristics
).
For negative charge pump outputs, the number of
required stages may be determined by:
where N
NEG
is rounded up to the nearest integer.
N
V
V
V
R
NEG
NEG
DROP
SUPN
TX LOAD
- 1 12
+
)
R
R
R
C f
C
TX
PCH ON
NCH ON
OUT CHP
(
2
+
)
(
)
(
)
=
+
+
1
1
N
V
V
V
V
R
POS
POS
SUPD
SUPP
DIODE
TX LOAD
-
- 1 12
)
+
CIRCUIT #1
3.3V
9V
100mA
-5V
2mA
24V
2mA
2.2
μ
H
>1A
4.7
μ
F
309k
49.9k
None
None
CIRCUIT #2
3.3V
9V
200mA
-5V
5mA
24V
5mA
4.7
μ
H
>1A
10
μ
F
309k
49.9k
None
None
CIRCUIT #3
3.3V
9V
200mA
-5V
5mA
24V
5mA
4.7
μ
H
>1A
20
μ
F
309k
49.9k
39k
*
100pF*
CIRCUIT #4
5V
12V
220mA
-5V
5mA
24V
5mA
6.8
μ
H
>1A
10
μ
F
429k
49.9k
None
None
CIRCUIT #5
5V
12V
220mA
-5V
5mA
24V
5mA
6.8
μ
H
>1A
20
μ
F
429k
49.9k
20k
*
200pF*
V
IN
V
MAIN
I
MAIN(MAX)
V
NEG
I
NEG
V
POS
I
POS
L
I
PEAK
C
OUT
R1
R2
R
COMP
C
COMP
Table 1. MAX1778/MAX1880/MAX1883 Component Values (f
OSC
= 1MHz)
*R
COMP
and C
COMP
are connected between the step-up converter
s output (V
MAIN
) and FB.
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