MAX1531ETJ+ Maxim Integrated Products, MAX1531ETJ+ Datasheet - Page 28

• Manufacturer Part Number: MAX1531ETJ+
• Description: IC PS CTRLR MULTI-OUTPUT 32TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1531ETJ+

• Applications: Five Power Supply Monitor
• Voltage - Supply: 4.5 V ~ 28 V
• Current - Supply: 1.7mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Voltage - Output: 1.25 ~ 16.5 V
• Number Of Outputs: 5
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Input: -
• Lead Free Status / Rohs Status: Details

Because R11 is less than 100kΩ, use 100kΩ for R11
and recalculate C10 as (step 3):
Use the standard value of 470pF for C10 and recalcu-
late the crossover frequency as:
Since the crossover frequency is less than 1/5th the switch-
ing frequency, 470pF is an acceptable value for C10.
Because the high-frequency pole of the current-mode
control is at 64kHz, the feed-forward capacitor is (step 4):
Use a standard value of 150pF for C23. The pole
formed by C23, R1 and R2 occur at 159kHz, above the
70.8kHz crossover frequency.
Because a ceramic output capacitor is used in the cir-
cuit of Figure1, the ESR zero occurs well above the
crossover frequency, so no additional compensation
capacitor (C2) is needed (step 5).
The MAX1530/MAX1531 step-down regulator’s output
voltage can be adjusted by connecting a resistive volt-
age-divider from the output to AGND with the center
tap connected to FB (Figure 1). Select R2 in the 5kΩ to
50kΩ range. Calculate R1 with the following equation:
where V
to approximately 0.6 × V
A signal diode, such as the 1N4148, works well in most
applications. If the input voltage goes below 6V, use a
small 100mA Schottky diode for slightly improved effi-
ciency and dropout characteristics. Do not use power
diodes, such as the 1N5817 or 1N4001, since high
junction capacitance can charge up VL to excessive
voltages.
Multiple-Output Power-Supply
Controllers for LCD Monitors
28
f
CROSSOVER
______________________________________________________________________________________
FB
C
C
10
23
= 1.238V, and V
≈
≈
2
2
R
≈
π
π
1
=
×
×
2
R
4 3
64
π
2
100
.
×
IN
kHz
×
kHz
⎛
⎜
⎝
470
1
μ
1
(V
V
V
S
OUT
OUT
IN
Output Voltage Selection
FB
×
×
pF
×
17 8
100
is up to 28V).
4180
.
−
may vary from 1.238V
×
Boost-Supply Diode
1
k
k
2000
⎞
⎟
⎠
Ω
Ω
=
=
140
370
=
70 8
pF
pF
.
kHz
For highest efficiency, always choose the lowest num-
ber of charge-pump stages that meet the output
requirement. The number of positive charge-pump
stages is given by:
where N
stages, V
the input voltage of the step-down regulator, V
forward voltage drop of the charge-pump diode, and
V
tor. Use V
The number of negative charge-pump stages is given by:
where N
stages, V
is the input voltage of the step-down regulator, V
the forward voltage drop of the charge-pump diode,
and V
ulator. Use V
The above equations are derived based on the
assumption that the first stage of the positive charge
pump is connected to V
negative charge pump is connected to ground.
Sometimes fractional stages are more desirable for bet-
ter efficiency. This can be done by connecting the first
stage to V
stage of the positive charger pump is powered from the
output of the step-down regulator V
tion becomes:
If the first stage of the negative charge pump is pow-
ered from the output of the step-down regulator V
then the equation becomes:
DROPOUT
DROPOUT
Selecting the Number of Charge-Pump Stages
NEG
POS
POS
NEG
N
N
DROPOUT
N
OUT
POS
NEG
is the dropout margin for the linear regula-
POS
DROPOUT
N
is the number of positive charge-pump
is the positive charge-pump output, V
is the number of negative charge-pump
is the negative charge-pump output, V
NEG
=
or another available supply. If the first
=
is the dropout margin for the linear reg-
=
−
−
V
V
V
POS
=
= 0.3V.
POS
NEG
−
V
= 0.3V.
NEG
+
+
V
+
V
V
IN
V
V
IN
V
IN
V
DROPOUT
IN
IN
DROPOUT
DROPOUT
− ×
+
and the first stage of the
− ×
− ×
− ×
2
V
2
2
2
DROPOUT
V
V
D
V
V
D
D
D
OUT
−
Charge Pumps
−
+
V
V
V
IN
, then the equa-
OUT
OUT
D
is the
OUT
IN
D
IN
is
is
,