MAX1578-MAX1579 Datasheet, PDF (1/13 Pages) Maxim Integrated Products – Complete Bias and White LED Power Supplies for Small TFT Displays

19-3359; Rev 0; 8/04
EVAALVUAAILTAIOBNLEKIT
Complete Bias and White LED Power Supplies
for Small TFT Displays
General Description
The MAX1578/MAX1579 provide four regulated outputs
to meet all the voltage requirements for small active-
matrix TFT-LCD displays in handheld devices where
minimum external components and high efficiency are
required. Each device consists of three advanced
charge pumps for LCD bias power and a step-up con-
verter for driving up to 8 series white LEDs for back-
lighting. The input voltage range is from 2.7V to 5.5V.
The charge pumps provide fixed +5V, +15V, and -10V
for the LCD bias circuits. No external diodes are need-
ed. A high-efficiency, fractional (1.5x/2x) charge pump
followed by a low-dropout linear regulator provides +5V
to power the source driver. Automatic mode changing
achieves the highest conversion efficiency. Two multi-
stage, high-voltage charge pumps generate +15V and
-10V to provide V_ON and V_OFF, respectively. Utilizing a
unique clocking scheme and internal drivers, these
charge pumps eliminate parasitic charge-current glitch-
es and reduce maximum input current, resulting in low
electromagnetic emissions. The outputs are sequenced
during startup and shutdown. In shutdown, the outputs
are discharged to zero.
The high-efficiency inductor step-up converter drives
up to 8 white LEDs in series with a constant current to
provide backlighting. The series connection allows the
LED currents to be identical for uniform brightness and
minimizes the number of traces to the LEDs. The
MAX1578 regulates constant LED current over the
entire temperature range. The MAX1579 features a tem-
perature derating function to avoid overdriving the
white LEDs during high ambient temperatures, enabling
higher drive current below +42°C.
The MAX1578/MAX1579 are available in space-saving
24-lead 4mm x 4mm thin QFN packages.
Applications
PDAs, Palmtops
Smart Phones
Internet Appliances
LCD Displays with White LED Backlight
Ordering Information
PART
MAX1578ETG
MAX1579ETG
TEMP RANGE PIN-PACKAGE
-40°C to +85°C
24 Thin QFN 4mm x 4mm
(T2444-4)
-40°C to +85°C
24 Thin QFN 4mm x 4mm
(T2444-4)
Features
♦ Four Regulators in One Package
♦ Bias Power Using Charge Pumps
+5V at 25mA for Source Driver
+15V at 100µA for V_ON
-10V at 100µA for V_OFF
No External Diodes Required
Output Sequencing
POS, NEG, and MAIN Are Autodischarged
During Shutdown
♦ LED Backlight Power Using Boost Converter
Series LED Connection for Uniform Illumination
Supports Up to 8 LEDs at 25mA (max)
900mW (max) Power
PWM or Analog Dimming Control
Overvoltage Protection
Low Input/Output Ripple
Soft-Start with Zero Inrush Current
Fast 1MHz PWM Operation for Small
Component Size
Temperature Derating Function (MAX1579)
♦ High Efficiency
Bias: 83% (5.0V at 25mA, 15V/-10V at 100µA)
LED: 84% (6 LEDs at 20mA)
♦ Uses Only Ceramic Capacitors and Only One
Inductor
♦ Independent Enable Inputs for LED and Bias
Power
♦ Thermal-Shutdown Protection
♦ 1µA Shutdown Current
♦ Tiny 4mm x 4mm Thin QFN Package
Pin Configuration
18 17 16 15 14 13
C1N 19
C2N 20
IN 21
C2P 22
C1P 23
V_DD 24
MAX1578
MAX1579
123456
12 GND
11 ONBIAS
10 NEG
9 CD2
8 CD1
7 PMPB
THIN QFN
4mm x 4mm
See Figure 3 for Typical Application Circuit.
________________________________________________________________ Maxim Integrated Products 1
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