MAX1516 Datasheet, PDF (12/26 Pages) Maxim Integrated Products – TFT-LCD DC-DC Converters with Operational Amplifiers

TFT-LCD DC-DC Converters with
Operational Amplifiers
Typical Operating Circuit
The MAX1518 Typical Operating Circuit (Figure 1) is a
complete power-supply system for TFT LCDs. The cir-
cuit generates a +13V source-driver supply and +24V
and -8V gate-driver supplies. The input voltage range
for the IC is from +2.6V to +5.5V. The listed load cur-
rents in Figure 1 are available from a +4.5V to +5.5V
supply. Table 1 lists some recommended components,
and Table 2 lists the contact information of component
suppliers.
Detailed Description
The MAX1516/MAX1517/MAX1518 contain a high-
performance step-up switching regulator, two low-cost
linear-regulator controllers, multiple high-current opera-
tional amplifiers, and startup timing and level-shifting
functionality useful for active-matrix TFT LCDs. Figure 2
shows the MAX1518 Functional Diagram.
Main Step-Up Regulator
The main step-up regulator employs a current-mode,
fixed-frequency PWM architecture to maximize loop
bandwidth and provide fast transient response to
pulsed loads typical of TFT-LCD panel source drivers.
The 1.2MHz switching frequency allows the use of low-
profile inductors and ceramic capacitors to minimize
the thickness of LCD panel designs. The integrated
high-efficiency MOSFET and the IC’s built-in digital
soft-start functions reduce the number of external com-
ponents required while controlling inrush currents. The
output voltage can be set from V_IN to 13V with an exter-
nal resistive voltage-divider. To generate an output volt-
age greater than 13V, an external cascoded MOSFET
is needed. See the Generating Output Voltages > 13V
section in the Design Procedures.
The regulator controls the output voltage and the power
delivered to the output by modulating the duty cycle (D)
of the internal power MOSFET in each switching cycle.
The duty cycle of the MOSFET is approximated by:
D ≈ ^{VMAIN − VIN}
V_MAIN
Table 1. Component List
DESIGNATION
DESCRIPTION
C1
22µF, 6.3V X5R ceramic capacitor (1210)
TDK C3225X5R0J227M
C2
22µF, 16V X5R ceramic capacitor (1812)
TDK C4532X5X1C226M
D1
3A, 30V Schottky diode (M-flat)
Toshiba CMS02
D2, D3
200mA, 100V, dual ultra-fast diodes (SOT23)
Fairchild MMBD4148SE
L1
3.0µH, 3A inductor
Sumida CDRH6D28-3R0
Q1
200mA, 40V pnp bipolar transistor (SOT23)
Fairchild MMBT3906
Q2
200mA, 40V npn bipolar transistor (SOT23)
Fairchild MMBT3904
Figure 3 shows the Functional Diagram of the step-up
regulator. An error amplifier compares the signal at FB
to 1.236V and changes the COMP output. The voltage
at COMP sets the peak inductor current. As the load
varies, the error amplifier sources or sinks current to the
COMP output accordingly to produce the inductor peak
current necessary to service the load. To maintain sta-
bility at high duty cycles, a slope-compensation signal
is summed with the current-sense signal.
On the rising edge of the internal clock, the controller
sets a flip-flop, turning on the n-channel MOSFET and
applying the input voltage across the inductor. The cur-
rent through the inductor ramps up linearly, storing
energy in its magnetic field. Once the sum of the cur-
rent-feedback signal and the slope compensation
exceeds the COMP voltage, the controller resets the
flip-flop and turns off the MOSFET. Since the inductor
current is continuous, a transverse potential develops
across the inductor that turns on the diode (D1). The
voltage across the inductor then becomes the differ-
ence between the output voltage and the input voltage.
Table 2. Component Suppliers
SUPPLIER
Fairchild
Sumida
TDK
Toshiba
PHONE
408-822-2000
847-545-6700
847-803-6100
949-455-2000
FAX
408-822-2102
847-545-6720
847-390-4405
949-859-3963
WEBSITE
www.fairchildsemi.com
www.sumida.com
www.component.tdk.com
www.toshiba.com/taec
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