MAX1884EUP-T Maxim Integrated, MAX1884EUP-T Datasheet - Page 29

• Manufacturer Part Number: MAX1884EUP-T
• Description: LCD Drivers Quad-Output TFT LCD DC-DC Converter with Buffer
• Manufacturer: Maxim Integrated

Specifications of MAX1884EUP-T

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

at higher output currents (see the Typical Operating
Characteristics ). So the maximum efficiency can be
approximated by:
for the positive charge pump, and:
for the negative charge pump, where V
positive charge pump’s diode supply (Figure 4).
Adjust the positive output voltage by connecting a volt-
age-divider from the output (V
the Typical Operating Circuit ). Adjust the negative
output voltage by connecting a voltage-divider from the
output (V
50kΩ to 100kΩ range. Higher resistor values improve
efficiency at low output current but increase output-
voltage error due to the feedback input bias current. For
the negative charge pump, higher resistor values also
reduce the load on the reference, which should not
exceed 50µA for greatest accuracy (including current
through the FLTSET resistors) to guarantee that V
remains in regulation (see the Electrical Characteristics ).
Calculate the remaining resistors with the following
equations:
where V
40V, and V
Increasing the flying capacitor (CX) value increases the
output current capability. Above a certain point,
increasing the capacitance has a negligible effect
because the output current capability becomes domi-
nated by the internal switch resistance and the diode
impedance. The flying capacitor’s voltage rating must
exceed the following:
for the positive charge pump, and:
Maxim Integrated
V
CXN POS
REF
NEG
η
NEG
POS
(
= 1.25V. V
) to FBN to REF. Select R4 and R6 in the
η
R3 = R4 [(V
can range from 0V to -40V.
≅
NEG
)
R5 = R6 |V
>
V
SUPD
≅
1 5
.
V
[
POS
V
V
SUPN
V
POS
+
NEG
SUPD
POS
NEG
V
Output-Voltage Selection
N
can range from V
SUPP
POS
/V
/V
REF
+
N
) to FBP to GND (see
REF
V
) - 1]
SUPP
|
Flying Capacitor
(
N
SUPD
MAX1778/MAX1880–MAX1885
1 -
Quad-Output TFT LCD DC/DC
)
]
SUPP
is the
REF
to
for the negative charge pump, where N is the stage
number in which the flying capacitor appears, and
V
(Figure 4). For example, the two-stage positive charge
pump in the typical application circuit (Figure 1) where
V
The flying capacitor in the first stage (C4) requires a
voltage rating over 12V. The flying capacitor in the
second stage (C6) requires a voltage rating over 24V.
Increasing the output capacitance or decreasing the
ESR reduces the output ripple voltage and the peak-to-
peak transient voltage. With ceramic capacitors, the
output-voltage ripple is dominated by the capacitance
value. Use the following equation to approximate the
required capacitor value:
where f
Characteristics ).
Use a bypass capacitor with a value equal to or greater
than the flying capacitor. Place the capacitor as close
as possible to the IC. Connect directly to power ground
(PGND).
Use Schottky diodes with a current rating equal to or
greater than two times the average charge-pump input
current, and a voltage rating at least 1.5 times V
for the positive charge pump and V
negative charge pump.
Adjust the linear-regulator output voltage by connecting
a voltage-divider from LDOOUT to FBL to GND
(Figure 5). Select R8 in the 5kΩ to 50kΩ range. Calculate
R7 with the following equation:
where V
1.25V to (V
0.8µA (max). For less than 0.5% error due to FBL input
bias current (I
Converters with Buffer
SUPD
SUPP
Low-Dropout Linear Regulator (MAX1778/
= V
is the positive charge pump’s diode supply
CHP
FBL
MAX1881/MAX1883/MAX1884 Only)
SUPD
SUPL
V
CXN NEG
R7 = R8 [(V
C
= 1.25V, and V
is typically f
FBL
OUT
(
), R8 must be less than 8kΩ.
= 8V contains two flying capacitors.
- 300mV). FBL’s input bias current is
≥
)
Charge-Pump Output Capacitor
Charge-Pump Rectifier Diodes
f
Charge-Pump Input Capacitor
> 1 5
CHP RIPPLE
LDOOUT
I
OSC
LOAD
. (
V
Output-Voltage Selection
LDOOUT
V
SUPN
/2 (see the Electrical
/V
FBL
N
) - 1]
)
can range from
SUPN
for the
SUPP
29