MAX1883EUP-T Maxim Integrated, MAX1883EUP-T Datasheet - Page 24

• Manufacturer Part Number: MAX1883EUP-T
• Description: LCD Drivers Quad-Output TFT LCD DC-DC Converter with Buffer
• Manufacturer: Maxim Integrated

Specifications of MAX1883EUP-T

• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Package / Case: TSSOP-20
• Mounting Style: SMD/SMT

Quad-Output TFT LCD DC/DC
Converters with Buffer
MAX1778/MAX1880–MAX1885
24
(I
1ms, soft-start enters phase II, and the current limit is
increased by another 25%. This process is repeated for
phase III. The maximum 1.5A (typ) current limit is
reached within 3072 clock cycles or when the output
reaches regulation, whichever occurs first (see the
startup waveforms in the Typical Operating
Characteristics ).
For the charge pumps (MAX1778/MAX1880–MAX1882
only), soft-start is achieved by controlling the rate of
rise of the output voltage. Both charge-pump output
voltages are controlled to be in regulation within 4096
clock cycles, irregardless of output capacitance and
load, limited only by the charge pump’s output imped-
ance. Although the MAX1883–MAX1885 controllers do
not include the charge pumps, the soft-start logic still
contains the 4096 clock cycle startup periods for both
charge pumps.
The MAX1778/MAX1880–MAX1885 feature dual-mode
operation to allow operation with either a preset fault
trip level or an adjustable trip level for the step-up con-
verter and positive charge-pump outputs. Connect
FLTSET to GND to select the preset 0.9
threshold. The fault trip level can also be adjusted by
connecting a voltage-divider from REF to FLTSET
(Figure 8). For greatest accuracy, the total load on the
reference (including current through the negative
charge-pump feedback resistors) should not exceed
50µA so that V
(see the Electrical Characteristics ). Therefore, select
R10 in the 100kΩ to 1MΩ range, and calculate R9 with
the following equation:
where V
x V
a maximum value of 50nA. For 1% error, the current
through R10 should be at least 100 times the FLTSET
input bias current (I
Once RDY is low, if the output of the main regulator or
either low-power charge pump falls below its fault
detection threshold, or if the input drops below its
undervoltage threshold, then RDY goes high impedance
and all outputs shut down; however, the reference
remains active. After removing the fault condition, toggle
shutdown (below 0.8V) or cycle the input voltage (below
0.2V) to clear the fault latch and reactivate the device.
The reference fault threshold is 1.05V. For the step-up
converter and positive charge-pump, the fault trip level is
LX(MAX)
REF
to 0.85 x V
REF
). If the output does not reach regulation within
= 1.25V, and V
R9 = R10 [(V
REF
REF
FLTSET
is guaranteed to be in regulation
. FLTSET’s input bias current has
Fault Trip Level (FLTSET)
REF
).
FLTSET
/V
FLTSET
can range from 0.67
Fault Condition
) - 1]

V
REF
fault
set by FLTSET (see the Fault Trip Level (
tion). For the negative charge pump, the fault threshold
measured at the charge-pump’s feedback input (FBN) is
140mV (typ).
RDY is an open-drain output. When the power-up
sequence for the main step-up converter and low-
power charge pumps has properly completed, the 14V
MOSFET turns on and pulls RDY low with a 125Ω (typ)
on-resistance. If a fault is detected on any of these
three outputs, the internal open-drain MOSFET appears
as a high impedance. Connect a 100kΩ pullup resistor
between RDY and IN for a logic-level output.
The voltage at REF is nominally 1.25V. The reference can
source up to 50µA with good load regulation (see the
Typical Operating Characteristics ). Connect a 0.22µF
ceramic bypass capacitor between REF and GND.
Thermal-overload protection limits total power dissipa-
tion in the MAX1778/MAX1880–MAX1885. When the
junction temperature exceeds T
sensor activates the fault protection, which shuts down
the controller, allowing the IC to cool. Once the device
cools down by 15°C, toggle shutdown (below 0.8V) or
cycle the input voltage (below 0.2V) to clear the fault
latch and reactivate the controller. Thermal-overload
protection protects the controller in the event of fault
conditions. For continuous operation, do not exceed
the absolute maximum junction-temperature rating of
T
The MAX1778/MAX1880–MAX1885s’ maximum power
dissipation depends on the thermal resistance of the IC
package and circuit board, the temperature difference
between the die junction and ambient air, and the rate
of any airflow. The power dissipated in the device
depends on the operating conditions of each regulator
and the buffer.
The step-up controller dissipates power across the
internal n-channel MOSFET as the controller ramps up
the inductor current. In continuous conduction, the
power dissipated internally can be approximated by:
J
= +150°C.
P
Operating Region and Power Dissipation
STEP UP
−
≈
×
⎡
⎢
⎢
⎣
⎛
⎜
⎝
Thermal-Overload Protection
I
R
MAIN MAIN
DS ON
(
V
Voltage Reference (REF)
IN
V
)
D
Power Ready ( R R D D Y Y )
⎞
⎟
⎠
2
J
= +160°C, a thermal
+
12
1
⎛
⎜
⎝
f
Maxim Integrated
FLTSET
OSC
V D
IN
L
⎞
⎟
⎠
2
) sec-
⎤
⎥
⎥
⎦