19-3359; Rev 0; 8/04
Co m p le t e Bia s a n d Wh it e LED P o w e r S u p p lie s
fo r S m a ll TFT Dis p la ys
Ge n e ra l De s c rip t io n
Fe a t u re s
♦ Four Regulators in One Package
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
re q uire d . Ea c h d e vic e c ons is ts of thre e a d va nc e d
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.
♦ 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
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
♦ 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
-10V to provide V
and V , respectively. Utilizing a
OFF
ON
Soft-Start with Zero Inrush Current
Fast 1MHz PWM Operation for Small
Component Size
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.
Temperature Derating Function (MAX1579)
♦ High Efficiency
Bias: 83% (5.0V at 25mA, 15V/-10V at 100µA)
LED: 84% (6 LEDs at 20mA)
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
minimize s the numb e r of tra c e s to the LEDs . The
MAX1578 re g ula te s c ons ta nt LED c urre nt ove r the
entire temperature range. The MAX1579 features a tem-
p e ra ture d e ra ting func tion to a void ove rd riving the
white LEDs during high ambient temperatures, enabling
higher drive current below +42°C.
♦ 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
P in Co n fig u ra t io n
The MAX1578/MAX1579 are available in space-saving
24-lead 4mm x 4mm thin QFN packages.
18 17 16 15 14 13
Ap p lic a t io n s
PDAs, Palmtops
12
11
10
9
C1N 19
GND
ONBIAS
NEG
Smart Phones
20
21
22
C2N
IN
Internet Appliances
CD2
MAX1578
MAX1579
C2P
LCD Displays with White LED Backlight
CD1
8
C1P 23
24
Ord e rin g In fo rm a t io n
7
PMPB
V
DD
PART
TEMP RANGE PIN-PACKAGE
1
2
3
4
5
6
24 Thin QFN 4mm x 4mm
MAX1578ETG
-40°C to +85°C
-40°C to +85°C
(T2444-4)
24 Thin QFN 4mm x 4mm
(T2444-4)
THIN QFN
4mm x 4mm
MAX1579ETG
See Figure 3 for Typical Application Circuit.
________________________________________________________________ Maxim Integrated Products
1
For pricing delivery, and ordering information please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.