MAX8571 MAXIM [Maxim Integrated Products], MAX8571 Datasheet - Page 9

• Manufacturer Part Number: MAX8571
• Description: High-Efficiency LCD Boost with True Shutdown
• Manufacturer: MAXIM [Maxim Integrated Products]

For the MAX8570/MAX8571/MAX8574 a feed-forward
capacitor (C4 in Figures 2 and 3) connected from the
output to FB improves stability over a wide range of
battery voltages. A 10pF capacitor is recommended for
the MAX8571 and MAX8574. A 10pF to 47pF capacitor
is recommended for the MAX8570. Note that increasing
C4 degrades line and load regulation.
A negative output voltage can be generated by adding
a diode/capacitor charge pump as shown in Figure 5. In
this configuration, the negative output is lower in magni-
tude than the positive output by a forward diode drop. If
there is little or no load on the positive output, the nega-
tive output drifts from its nominal voltage. To prevent
this, it may be necessary to preload the positive output
with a few hundred microamps, which can be done by
selecting lower than normal values of R1 and R2.
Negative Output Voltage for LCD Bias
Applications Information
_______________________________________________________________________________________
High-Efficiency LCD Boost
Careful printed circuit layout is important for minimizing
ground bounce and noise. Keep the GND pin and
ground pads for the input and output capacitors as
close together as possible. Keep the connection to LX
as short as possible. Locate the feedback resistors as
close as possible to the FB pin and keep the feedback
traces routed away from noisy areas such as LX. Refer
to the MAX8571EVKIT for a layout example.
TRANSISTOR COUNT: 742
PROCESS: BiCMOS
with True Shutdown
Chip Information
PC Board Layout
9