MAX1542 Datasheet, PDF (14/20 Pages) Maxim Integrated Products – TFT LCD DC-to-DC Converter with Operational Amplifiers

TFT LCD DC-to-DC Converter with
Operational Amplifiers
COMP
FB
FREQ*
NEG1
OUT1
POS1
1.24V
OSCILLATOR
5µA
ERROR
AMPLIFIER
SLOPE
COMPEN-
SATION
ERROR
COMPARATOR
CLOCK
∑
CONTROL
AND DRIVER
LOGIC
CURRENT
SENSE
SOFT-
START
N
5µA
SWITCH
CONTROL
(SEE FIGURE 4)
IN
LX
PGND
AGND
SUP
EXT*
NEG2
OUT2
POS2
MAX1542
MAX1543
*MAX1543 ONLY.
Figure 3. Functional Diagram
DEL
SRC COM DRN*
CTL
Thermal-Overload Protection
Thermal-overload protection prevents excessive power
dissipation from overheating the MAX1542/MAX1543.
When the junction temperature exceeds T_J = +160°C, a
thermal sensor immediately activates the fault protec-
tion, which shuts down the device, allowing the IC to
cool. The input voltage must fall (below V_UVLO) to clear
the fault latch and reactivate the controller.
Thermal-overload protection protects the controller in
the event of fault conditions. For continuous operation,
do not exceed the absolute maximum junction-temper-
ature rating of T_J = +150°C.
Applications Information
Inductor Selection
The primary considerations in inductor selection are
inductor physical shape, circuit efficiency, and cost.
The factors that determine the inductance value are
input voltage, output voltage, switching frequency, and
maximum output current. Final inductor selection
includes ensuring the chosen inductor meets the appli-
cation’s peak current and RMS current requirements.
Very high inductance values minimize the current ripple
and therefore reduce the peak current, which decreas-
es core losses in the inductor and I²R losses in the cir-
cuit’s entire power path. However, large inductance
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