MAX1661 Datasheet, PDF (8/16 Pages) Maxim Integrated Products – Active-Matrix Liquid Crystal Display AMLCD Supply

Active-Matrix Liquid Crystal Display
(AMLCD) Supply
V_OUT2-
-10V
V_OUT2+
28V
REF
FB2-
LX2P
INP
IN
DC-DC 2
MAX1664
LX2N
FB2+
PGND2
PLLC
÷4
÷2
BPCLK
PHASE
DET
VCO
FPLL
÷N
LX1
DC-DC 1
FB1
1.25V
REF
PGND1
BPV_DD
BPDRV
BPV_SS
SHDN
V_SUPPLY
2.8V TO 5.5V
V_OUT1
5.5V
BACKPLANE
DRIVER
IN REF GND
RDY
GND
REF
Figure 1. Functional Diagram
_______________Detailed Description
The MAX1664 combines power supply and backplane
drive circuitry for active matrix thin-film-transistor (TFT)
liquid crystal displays (LCD) into one IC. Included are a
pulse-width-modulation (PWM) boost converter, a dual-
output (positive and negative) converter using one
inductor, an LCD backplane driver, and a phase-
locked loop (PLL) to synchronize all three outputs to the
backplane clock.
A high switching frequency (1MHz nominal) and phase-
locked operation allow the use of small, minimum-
height external components while maintaining low
output noise. Output voltages are adjustable to +5.5V
(DC-DC 1) and to +28V and -10V (DC-DC 2). The nega-
tive output voltage can be set to as low as -20V with
additional components.
The frequency ratio between the DC-DC 1 converter
and the backplane clock can be set to 16, 24, or 32.
This flexibility allows high DC-DC converter frequencies
to be used with LCD backplane clock rates ranging
from 20kHz to 72kHz.
Start-Up
At start-up, both converters remain disabled until V_REF
reaches 90% of its nominal value. V_OUT1 is activated
first. Once V_OUT1 is regulated, V_OUT2- is enabled.
V_OUT2+ is held at 0 until V_OUT2- is within 90% of its reg-
ulation target. All three outputs power up in a similar
order when power is applied or when coming out of
shutdown. See the Out-of-Shutdown Sequence photo in
the Typical Operating Characteristics section.
DC-DC 1 Boost Converter
DC-DC 1 uses a current-mode boost PWM architecture
to produce a positive regulated voltage, adjustable
from 3V to 5.5V (but not less than V_IN). This converter
uses an internal N-channel MOSFET with a maximum
on-resistance of 0.5Ω. Cycle-by-cycle peak current lim-
iting protects the switch under fault conditions. Upon
start-up, DC-DC 1 is the first converter to be enabled.
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