MAX8710EVKIT Maxim Integrated Products, MAX8710EVKIT Datasheet - Page 22

• Manufacturer Part Number: MAX8710EVKIT
• Description: Power Management Modules & Development Tools MAX8710 KIT MAX8710 KIT
• Manufacturer: Maxim Integrated Products

Specifications of MAX8710EVKIT

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Low-Cost, Linear-Regulator
LCD Panel Power Supplies
where R1 is the upper resistor of the feedback divider
and f
quency (f
approximately 80kHz; for MAX8761, f
160kHz. The value of R1 was calculated in the Output-
Voltage Selection section to set V
for unity gain frequency (f
and V
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
tors (V
MAX8712), V
charge-pump diode, and V
the internal switches. Use V
The number of negative charge-pump stages is given by:
where n
stages and V
tor output.
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 another available supply, such as a 5V supply.
If the first charge-pump stage is powered from 5V, then
the above equations become:
22
INPUT
______________________________________________________________________________________
u
FBL
SUPCP
is the unity gain frequency. The unity gain fre-
is the supply voltage for the charge-pump regula-
NEG
ƒ
POS
n
n
P
, and R1 to calculate the value of C1.
n
n
ZERO
POS
NEG
u
POS
NEG
is the positive charge-pump regulator output,
) for the MAX8710/MAX8711/MAX8712 is
, MAX8710/MAX8761 or V
GOFF
DIODE
is the number of positive charge-pump
is the number of negative charge-pump
=
=
=
=
=
2
V
V
−
π
is the negative charge-pump regula-
INPUT
V
P
V
V
R C
P
is the forward-voltage drop of the
−
GOFF
INPUT
1
Number of Charge-Pump Stages
V
V
1 1
V
+
INPUT
INPUT
GOFF
+
Charge-Pump Regulators
MAIN
V
SWITCH
−
=
V
SWITCH
SWITCH
u
+
SWITCH
), the ratio between V
−
2
−
−
+
V
V
2
×
and the first stage of the
OUTL
SWITCH
2
2
V
×
V
×
SWITCH
ƒ
×
DIODE
−
= 0.3V.
is the voltage drop of
OUTL
U
V
V
−
5
/
DIODE
V
DIODE
V
u
V
DIODE
V
FBL
+
OUTL
is approximately
SUPCP
. Use the value
5
V
, MAX8711/
OUTL
Adjust the positive charge-pump-regulator output volt-
age by connecting a resistive voltage-divider from the
regulator output V
ed to FBP (Figure 1). Select the lower resistor of divider
R4 in the range of 10kΩ to 50kΩ. Calculate upper resistor
R3 with the following equation:
where V
positive charge-pump regulator.
Adjust the negative charge-pump-regulator output volt-
age by connecting a resistive voltage-divider from the
negative charge-pump output V
center tap connected to FBN (Figure 1). Select R6 in
the 20kΩ to 100kΩ range. Calculate R5 with the follow-
ing equation:
where V
point of the negative charge-pump regulator.
Increasing the flying-capacitor (C
effective source impedance and increases the output-
current capability of the charge pump. Increasing the
capacitance indefinitely has a negligible effect on out-
put-current capability because the internal switch resis-
tance 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 is used, and V
charge-pump regulators (V
or V
Use an input capacitor with a value equal to or greater
than the flying capacitor. Place the capacitor as close
to the IC as possible. Connect the capacitor directly
to PGND.
OUTL
REF
FBP
, MAX8711/MAX8712).
= 5V and V
= 2.5V (typ) is the regulation point of the
R
5
R
=
P
3
V
INPUT
to GND with the center tap connect-
R
CX
=
6
R
×
Charge-Pump Input Capacitor
> n x V
4
FBN
is the supply voltage for the
V
×
V
FBN
SUPCP
REF
Output-Voltage Selection
⎛
⎜
⎝
= 250mV is the regulation
V
INPUT
V
FBP
−
P
−
GOFF
, MAX8710/MAX8761
V
V
X
GOFF
−
FBN
) value lowers the
1
Flying Capacitor
⎞
⎟
⎠
to REF with the