MAX1542 Datasheet, PDF (10/20 Pages) Maxim Integrated Products – TFT LCD DC-to-DC Converter with Operational Amplifiers

TFT LCD DC-to-DC Converter with
Operational Amplifiers
PIN
MAX1542 MAX1543
14
14
—
15
16
16
17
17
18
18
19
19
—
20
Pin Description (continued)
NAME
FUNCTION
IN
FREQ
FB
COMP
Supply Voltage. IN can range from 2.6V to 5.5V.
Oscillator Frequency Select Input. Pull FREQ low or leave it unconnected for 640kHz
operation. Connect FREQ high for 1.2MHz operation. This input has a 5µA pulldown
current.
Step-Up Converter Feedback Input. Regulates to 1.24V (nominal). Connect a resistor-
divider from the output (V_MAIN) to FB to analog ground (AGND). Place the resistor-divider
within 5mm of FB.
Step-Up Regulator Error Amplifier Compensation Point. Connect a series RC from COMP
to AGND. See the Loop Compensation section for component selection guidelines.
High-Voltage Switch Delay Input. Connect a capacitor from DEL to AGND to set the high-
voltage switch startup delay. A 5µA current source charges C_DEL.
For the MAX1542, the high-voltage switch between SRC and COM is disabled until V_DEL
exceeds 1.24V. Following the delay period, CTL controls the state of the high-voltage
DEL switch.
CTL
DRN
For the MAX1543, the switches between SRC, COM, and DRN are disabled and a 1kΩ
pulldown between COM and PGND is enabled until V_DEL exceeds 1.24V. Following the
delay period, the 1kΩ pulldown is released and CTL controls the state of the high-voltage
switches (see the Delay Control Circuit section).
High-Voltage Switch Control Input. When CTL is high, the high-voltage switch between
COM and SRC is on and the high-voltage switches between COM and DRN (MAX1543)
are off. When CTL is low, the high-voltage switch between COM and SRC is off and the
high-voltage switches between COM and DRN (MAX1543) are on. CTL is inhibited by the
undervoltage lockout and when V_DEL is less than 1.24V.
Switch Input. Drain of the internal high-voltage back-to-back P-channel MOSFETs
connected to COM.
Typical Application Circuits
The MAX1542 typical application circuit (Figure 1) and
the MAX1543 typical application circuit (Figure 2) gen-
erate an +8V source driver supply and approximately
+22V and -7V gate driver supplies for TFT displays. The
input voltage is from +2.6V to +5.5V. Table 1 lists rec-
ommended components and Table 2 lists contact infor-
mation for component suppliers.
Detailed Description
The MAX1542/MAX1543 include a high-performance
step-up regulator, two high-current operational ampli-
fiers, and startup timing and level-shifting functionality
useful for active matrix TFT LCDs. Figure 3 shows the
MAX1542/MAX1543 functional diagram.
Main Step-Up Converter
The MAX1542/MAX1543 main step-up converter
switches at 1.2MHz or 640kHz (MAX1543 only) (see the
Oscillator Frequency (FREQ) section). The devices
employ a current-mode, fixed-frequency, pulse-width
modulation (PWM) architecture to maximize loop band-
width providing fast transient response to pulsed loads
found in source drivers for TFT LCD panels. The high-
switching frequency also allows the use of low-profile
inductors and capacitors to minimize the thickness of
LCD panel designs. The integrated high-efficiency
MOSFET and the IC’s built-in digital soft-start function
reduce the number of external components required
while controlling inrush current. The output voltage of
the main step-up converter (V_MAIN) can be set from V_IN
to 13V with an external resistive voltage-divider at FB.
10 ______________________________________________________________________________________