Rainbow Electronics MAX1543 - Manual (Page 14)

MAX1542/MAX1543
TFT LCD DC-to-DC Converter with
Operational Amplifiers
14 ______________________________________________________________________________________
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 I
2 R losses in the cir-
cuit’s entire power path. However, large inductance
PGND
LX
FREQ*
FB
COMP
5 µA
N
ERROR
COMPARATOR
ERROR
AMPLIFIER
CLOCK
MAX1542
MAX1543
CURRENT
SENSE
CONTROL
AND DRIVER
LOGIC
SOFT-
START
SLOPE
COMPEN-
SATION
OSCILLATOR
1.24V
∑
IN
AGND
SWITCH
CONTROL
(SEE FIGURE 4)
OUT2
NEG2
POS2
OUT1
NEG1
POS1
DEL CTL SRC COM DRN*
SUP
EXT*
*MAX1543 ONLY.
5 µA
Figure 3. Functional Diagram