MAX17075ETG+ Maxim Integrated Products, MAX17075ETG+ Datasheet - Page 20

• Manufacturer Part Number: MAX17075ETG+
• Description: IC DC-DC CONV W/CHRG PUMP 24TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX17075ETG+

• Applications: LCD TV/Monitor
• Current - Supply: 4mA
• Voltage - Supply: 2.3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Boost Regulator with Integrated Charge Pumps,
Switch Control, and High-Current Op Amp
To further optimize transient response, vary R
20% steps and C
transient-response waveforms.
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
regulator, V
pump regulators, V
charge-pump diode, and V
margin for the regulator. Use V
The number of negative charge-pump stages is given by:
where n
stages and V
pump regulator.
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.
Increasing the flying capacitor C
and DRVP) value lowers the effective source impedance
and increases the output current capability. Increasing
the capacitance indefinitely has a negligible effect on
output current capability because the internal switch
resistance and the diode impedance place a lower limit
on the source impedance. A 0.1µF ceramic capacitor
works well in most low-current applications. The flying
capacitor’s voltage rating must exceed the following:
where n is the stage number in which the flying capaci-
tor appears.
20
______________________________________________________________________________________
Selecting the Number of Charge-Pump Stages
NEG
POS
GON
η
POS
SUP
GOFF
η
is the number of positive charge-pump
is the number of negative charge-pump
is the output of the positive charge-pump
NEG
=
is the supply voltage of the charge-
V
COMP
GON
=
is the output of the negative charge-
D
V
−
is the forward voltage drop of the
CX
V
Charge-Pump Regulators
GOFF
+
AVDD
V
V
in 50% steps while observing
> ×
V
SUP
SUP
DROPOUT
n V
+
DROPOUT
− ×
− ×
DROPOUT
and the first stage of the
V
SUP
2
2
DROPOUT
X
(connected to DRVN
V
V
D
D
−
Flying Capacitors
V
AVDD
is the dropout
= 600mV.
COMP
in
Increasing the output capacitance or decreasing the
ESR reduces the output ripple voltage and the peak-to-
peak transient voltage. With ceramic capacitors, the
output voltage ripple is dominated by the capacitance
value. Use the following equation to approximate the
required capacitor value:
where C
pump, I
pump, and V
output ripple, and f
Adjust the positive charge-pump regulator’s output volt-
age by connecting a resistive voltage-divider from the
REG P output to GND with the center tap connected to
FBP (Figure 1). Select the lower resistor of divider R16
in the 10kΩ to 30kΩ range. Calculate the upper resistor
R15 with the following equation:
where V
Adjust the negative charge-pump regulator’s output
voltage by connecting a resistive voltage-divider from
V
(Figure 1). Select R6 in the 35kΩ to 68kΩ range.
Calculate R7 with the following equation:
where V
only source up to 50µA, using a resistor less than 35kΩ
for R6 results in higher bias current than REF can supply.
XAO threshold voltage can be adjusted by connecting
a resistive voltage-divider from input V
the center tap connected to RSTIN (see Figure 1).
Select R12 in the 10kΩ to 50kΩ range. Calculate R11
with the following equation:
where V
V
R11 and R12 close to the IC.
GOFF
INXAO
to REF with the center tap connected to FBN
FBN
FBP
RSTIN
is the desired XAO threshold voltage. Place
OUT
LOAD
= 1.25V (typical).
= 250mV, V
_
C
RIPPLE_CP
CP
, the RSTIN threshold set point, is 1.25V.
OUT CP
_
Set the XAO Threshold Voltage
CP
R
R
R
11
is the output capacitor of the charge
15
7
_
OSC
is the load current of the charge
=
=
=
R
R
Charge-Pump Output Capacitor
R
6
12
≥
16
is the switching frequency.
is the peak-to-peak value of the
×
REF
2
×
V
×
f
OSC RIPPLE CP
V
FBN
⎛
⎝ ⎜
⎛
⎝ ⎜
REF
= 1.25V. Note that REF can
V
I
V
LOAD CP
Output Voltage Selection
V
INXAO
V
RSTIN
GON
V
FBP
−
−
V
V
GOFF
_
FBN
−
−
1
1
⎞
⎠ ⎟
_
⎞
⎠ ⎟
IN
to GND with