MAX1884EUP-T Maxim Integrated, MAX1884EUP-T Datasheet - Page 21

• 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

The switching waveforms appear noisy and asynchro-
nous when light loading causes pulse-skipping opera-
tion; this is a normal operating condition that improves
light-load efficiency.
Maxim Integrated
Figure 3. Discontinuous-to-Continuous Conduction Crossover
Point
Figure 4. Low-Power Charge Pump Block Diagram
2.7V TO 13V
V
V
SUPP
V
SUPD
POS
t
ON
V
V
POS
REF
= 1.25V
= 1 +
( )
C
R3
R4
OUT(POS)
V
t
REF
OFF
D2
D3
R3
R4
C
X(POS)
TIME
FBP
SUPP
DRVP
1.25V
V
REF
MAX1778/MAX1880–MAX1885
GND
Quad-Output TFT LCD DC/DC
I
I
PEAK
LOAD
MAX1778
MAX1880
MAX1881
MAX1882
OSC
The MAX1778/MAX1880–MAX1882 controllers contain
two independent low-power charge pumps (Figure 4).
One charge pump inverts the input voltage and pro-
vides a regulated negative output voltage. The second
charge pump doubles the input voltage and provides a
regulated positive output voltage. The controllers
contain internal p-channel and n-channel MOSFETs to
control the power transfer. The internal MOSFETs
switch at a constant frequency (fCHP = fOSC/2).
During the first half-cycle, the n-channel MOSFET turns
on and charges flying capacitor C
This initial charge is controlled by the variable
n-channel on-resistance. During the second half-cycle,
the n-channel MOSFET turns off and the p-channel
MOSFET turns on, level shifting C
This connects C
capacitor C
plus a diode drop (V
level-shifted flying capacitor voltage (V
V
the diode (D3) turns off.
Converters with Buffer
SUPP
Dual Charge-Pump Regulator (MAX1778/
), charge flows from C
PGND
OUT(POS)
X(POS)
SUPN
DRVN
REF
FBN
. If the voltage across C
POS
MAX1880–MAX1882 Only)
C
X(NEG)
in parallel with the reservoir
+ V
R6
C
0.22µF
D4
D5
DIODE
REF
X(POS)
Positive Charge Pump
R5
X(POS)
) is smaller than the
X(POS)
to C
V
V
NEG
REF
= 1.25V
by V
= -
C
OUT(POS)
OUT(NEG)
( )
R5
R6
V
2.7V TO 13V
(Figure 4).
CX(POS)
SUPP
SUPN
V
V
REF
OUT(POS)
NEG
volts.
until
21
+