MAX1889ETE+ Maxim Integrated Products, MAX1889ETE+ Datasheet - Page 25

• Manufacturer Part Number: MAX1889ETE+
• Description: IC PWR SUP TRPL LCD 16-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1889ETE+

• Applications: Controller, TFT, LCD
• Voltage - Input: 2.7 ~ 5.5 V
• Number Of Outputs: 3
• Voltage - Output: 2.7 ~ 13 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The maximum output voltage of the step-up regulator is
13V, which is limited by the absolute maximum rating of
the internal power MOSFET. To achieve higher output
voltage, an external N-channel MOSFET can be cas-
coded with the internal FET (Figure 9). Since the gate of
the external FET is biased from the input supply, use a
logic-level FET to ensure that the FET is fully enhanced
at the minimum input voltage. The current rating of the
FET needs to be higher than the internal current limit.
The power-up sequencing of the linear regulators can be
controlled using external delays. Figure 10 shows an
application where the negative linear-regulator output
powers up with a certain delay after the positive linear
regulator reaches regulation. The resistors R1, R2, and
the capacitor C form an RC network that provides the
power-up delay. The time constant of this RC network is:
Select the ratio of R1 and R2 so that:
or:
With this R1/R2 ratio, the power-up delay can be calcu-
lated as:
where V
0.125V is the FBN regulation point.
As a design example, assume the positive linear-regu-
lator output V
output V
t
The ratio of R1 and R2 should be:
D
is 4ms:
D
N
is the forward voltage drop of the diode and
is -9V, and the required power-up delay time
PL
V
τ
Additional Application Circuits
N
D
Operation with Output Voltage >13V
is +20V, the negative charge-pump
______________________________________________________________________________________
R
=
1
R
τ
+
τ =
ln
2
R
Changing Power-Up Sequence
R
R
R
R





2
1
2
1
2
R
R
V
V
+
1
1
D
PL
= -
=
×
+
V
Triple-Output TFT LCD Power Supply
-
PL
R
R
20
R
0 125
9
2
2
V
1
.
V
R
PL
R
+
N
C
1
1
R
R
+
2
1
V
R





2
=
0
The required RC time constant is:
Choose C = 0.1µF, then R1//R2 = 16.8kΩ. Use stan-
dard resistor values: R1 = 56kΩ and R2 = 24kΩ.
If the input protection MOSFET is not needed, disable
the input overcurrent comparator by connecting the
OCP pin to ground, the OCN pin to V
GATE pin floating (Figure 11).
The reference voltage for the Gamma correction resis-
tor string can be produced using the linear-regulator
controller. If the voltage difference between the main
boost voltage (V
age is 400mV or greater, the emitter of the PNP pass
transistor should be connected to V
Figure 9. Operation with Output Voltage >13V Using Cascoded
MOSFET
with Fault Protection
V
IN
V
N
REGULATOR
MAX1889
τ =
STEP-UP
Generating Gamma Reference Voltage
MAIN
ln






0 7 0 125
Disabling Input MOSFET Switch
) and the Gamma reference volt-
20
.
4
LX
ms
20 9
-
9
.
+
PGND
FB






=
1 68
MAIN
.
ms
.
IN
. Leave the
V
V
15V
P
MAIN
25