MAX1885EUP-T Maxim Integrated, MAX1885EUP-T Datasheet - Page 27

• Manufacturer Part Number: MAX1885EUP-T
• Description: LCD Drivers Quad-Output TFT LCD DC-DC Converter with Buffer
• Manufacturer: Maxim Integrated

Specifications of MAX1885EUP-T

• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Package / Case: TSSOP-20
• Mounting Style: SMD/SMT

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
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 can be determined by:
where V
(Figure 4), V
and R
*R
Table 1. MAX1778/MAX1880/MAX1883 Component Values (f
Maxim Integrated
COMP
N
POS
TX
MAIN
Selecting the Number of Charge-Pump Stages
I
MAIN(MAX)
and C
SUPD
C
R
Charge Pumps (MAX1778/ MAX1880/
V
V
I
C
V
is the charge pump’s output impedance. The
I
I
PEAK
COMP
COMP
V
MAIN
NEG
POS
NEG
POS
R1
R2
OUT
L
IN
).
≥
DIODE
COMP
⎛
⎜
⎝
is the positive charge-pump diode supply
V
SUPP
are connected between the step-up converter’s output (V
is the diode’s forward voltage drop,
- 1 1 2
MAX1881/MAX1882 Only)
V
. (
POS
CIRCUIT 1
100mA
49.9kΩ
V
309kΩ
2.2µH
4.7µF
None
None
3.3V
2mA
2mA
>1A
24V
DIODE
-5V
9V
-
V
SUPD
+
Rectifier Diode
R I
TX LOAD
MAX1778/MAX1880–MAX1885
CIRCUIT 2
Quad-Output TFT LCD DC/DC
200mA
49.9kΩ
309kΩ
4.7µH
None
None
10µF
5mA
5mA
3.3V
>1A
24V
-5V
)
9V
⎞
⎟
⎠
charge pump’s output impedance can be approximat-
ed using the following equation:
where the charge pump’s switching frequency (f
equal to 0.5 x f
tance (R
on-resistance (R
Characteristics ).
For negative charge-pump outputs, the number of
required stages can be determined by:
where N
Converters with Buffer
N
CIRCUIT 3
R
NEG
200mA
49.9kΩ
100pF*
TX
309kΩ
39kΩ*
4.7µH
20µF
3.3V
5mA
5mA
>1A
24V
-5V
MAIN
9V
NEG
PCH(ON)
=
≥
) and FB.
+
2
is rounded up to the nearest integer.
(
⎛
⎜
⎝
⎛
⎜
⎝
R
C
OSC
V
PCH ON
SUPN
) is 10Ω, and the n-channel MOSFET’s
OUT CHP
NCH(ON
OSC
, the p-channel MOSFET’s on-resis-
(
1
f
- 1 1 2
)
CIRCUIT 4
= 1MHz)
220mA
49.9kΩ
+
429kΩ
6.8µH
None
None
10µF
. (
5mA
5mA
⎞
⎟
⎠
>1A
)) is 4Ω (see the Electrical
12V
24V
-5V
5V
R
NCH ON
V
V
DROP
NEG
(
)
+
)
+
R I
⎛
⎜
⎝
TX LOAD
C f
CIRCUIT 5
X CHP
220mA
49.9kΩ
200pF*
429kΩ
20kΩ*
6.8µH
1
20µF
5mA
5mA
>1A
12V
24V
-5V
5V
CHP
⎞
⎟
⎠
)
⎞
⎟
⎠
) is
27