MAX1889ETE+ Maxim Integrated Products, MAX1889ETE+ Datasheet - Page 20

• 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

Triple-Output TFT LCD Power Supply
with Fault Protection
If the junction temperature is +100°C, the maximum on-
state resistance overtemperature is:
For given R1 and R2 values, the ideal ratio of R3/R4
can be determined:
To consider the effect of resistor tolerance, comparator
offset, and input voltage variation, the minimum threshold
equation is:
where V
input voltage, ε is the tolerance of the resistors and the
5mV is the worst-case input offset voltage of the com-
parator. To simplify the equation, define a constant k as
follows:
The minimum threshold equation becomes:
Solving for R3/R4 yields:
The R3/R4 ratio guarantees the required minimum level
for I
20
V
(
R
V
L(MAX)
IN MIN
DS MAX
IN MIN
______________________________________________________________________________________
(
R
R
R
R
(
(
V
(
V
IN MIN
3
4
3
4
IN MIN
IN(MIN)
(
= ×
=
)
(
. The typical overcurrent threshold is given by:
)
×
k
R
-
)
I
R
1
L MAX
=
)
R
1 1
(
+
)





×
70
2
×
-
R
V
I
V
( )
k R
is the minimum expected value of the
L MAX
IN MIN
2
m
IN MIN
R
(
×
-
)
(
×
2
Ω
ε
(
×
R
× +
V
1
R
× +
+
2
IN PEAK MAX
(
+
DS MAX
1
)
R
)
[
k =
)
1 0 005
R
×
-
2
-
×
(
I
2
I
R
L MAX
ε
× +
(
R
)
1
DS MAX
1
+
(
.
1
2
+
- ε
5
(
+ ×
)
ε
mV
R
)
ε
(
k R
)
×
2
)
×
×
V
+
R
=
(
IN
R
)
3
100 25
5
)
1
DS MAX
)
mV
× +
×
×
+
(
1
R
(
R
5
-
R
=
3
DS MAX
mV
4
k R
ε
+ ×
×
)
×
)
(
k R
]
)
+
( )
1
=
-
R
-
4
1
100
4
ε





)
4
×
-
( )
m
1
1
-
Ω
ε
The following example shows how to apply the above
equations in the design. If 1% resistors are used, then
ε = 0.01. To set V
R1 = 51.1kΩ and R2 = 150kΩ. Assume that the mini-
mum input voltage is 2.7V and the typical input voltage
is 3.3V, the average inductor current at maximum load
is 1.25A, and the maximum R
If R4 =150kΩ, then R3 = 39.2kΩ. The typical overcurrent
threshold is:
For highest efficiency, always choose the lowest num-
ber of charge-pump stages that meets the output
requirement.
The number of positive charge-pump stages is given by:
where N
stages, V
V
forward voltage drop of the charge-pump diode, and
V
tor. Use V
MAIN
DROPOUT
R
R
3
4
I
TH TYP
=
=
0 9802
_
0 2637
is the main step-up regulator output, V
.
.
I
TH TYP
POS
DROPOUT
PL
_
N
=
is the dropout margin for the linear regula-
=
×
POS
0 047
is the number of positive charge-pump
is the positive linear-regulator output,





4 15
.
3 3
2 7
.
.
=
k
.
=
=
R
V
V
OCP
A
V
Ω
1 0 01
V
DS TYP
1 0 01
×
IN TYP
= 2V.
+
PL
-
150
×
(
(
.
.
to be around 75% of V




+
1
k
V
2 7
-
V
Ω
)
MAIN
)
=
.
150
DROPOUT
150
+
×
0 9802
V
0 9802 51 1
.
150




DS(ON)
-
Selecting the Number of
.
k
k
1
1 25
Ω
Ω
-
.
- 2
k
R
R
×
Charge-Pump Stages
×
Ω
×
2
A
4
(
(
×
39 2
V
×
51 1
×
×
-
D
of P1 is 100mΩ:
(
Charge Pumps
0 1
(
V
R
R
.
.
.
MAIN
.
3
1
k
Ω
k
k
+
Ω
+
Ω
Ω
R
R
+
+
2
+
4
150
150
)
)
0 005




.
IN
k
D
k
, select
Ω
Ω
V
is the
)
)
-




1




