MAX1682 Maxim, MAX1682 Datasheet - Page 6

• Manufacturer Part Number: MAX1682
• Description: Switched-Capacitor Voltage Doublers
• Manufacturer: Maxim

Conversion losses occur during the charge transfer
between C1 and C2 when there is a voltage difference
between them. The power loss is:
where V
determined by the output capacitor and load current
(see Output Capacitor section). Choose capacitor val-
ues that decrease the output resistance (see Flying
Capacitor section).
To maintain the lowest output resistance, use capaci-
tors with low ESR. Suitable capacitor manufacturers are
listed in Table 1. The charge-pump output resistance is
a function of C1 and C2’s ESR and the internal switch
resistance, as shown in the equation for R
Efficiency Considerations section.
Minimizing the charge-pump capacitor’s ESR mini-
mizes the total resistance. Suggested values are listed
in Tables 2 and 3.
Switched-Capacitor Voltage Doublers
Table 1. Recommended Capacitor Manufacturers
Table 2. Suggested Capacitor Values for
Low Output Resistance
6
P
Surface-Mount Tantalum
Surface-Mount Ceramic
MAX1682
MAX1683
CONVERSION LOSS
1 2
PART
_______________________________________________________________________________________
/ C2 2V
PRODUCTION METHOD
RIPPLE
OUT RIPPLE
FREQUENCY
is the peak-to-peak output voltage ripple
Applications Information
V
(kHz)
12
35
1 2
/ C1 4V
Flying Capacitor (C1)
CAPACITOR
V
VALUE (µF)
2
RIPPLE
3.3
10
MANUFACTURER
IN
2
Sprague
Matsuo
Matsuo
x f
AVX
AVX
V
OSC
OUT
TYPICAL
R
OUT
OUT
2
20
20
in the
(Ω)
593D, 595D
SERIES
X7R
X7R
TPS
Using a larger flying capacitor reduces the output
impedance and improves efficiency (see the Efficiency
Considerations section). Above a certain point, increas-
ing C1’s capacitance has a negligible effect because
the output resistance becomes dominated by the inter-
nal switch resistance and capacitor ESR (see the
Output Resistance vs. Capacitance graph in the
Typical Operating Characteristics ). Table 2 lists the
most desirable capacitor values—those that produce a
low output resistance. But when space is a constraint, it
may be necessary to sacrifice low output resistance for
the sake of small capacitor size. Table 3 demonstrates
how the capacitor affects output resistance.
Increasing the output capacitance reduces the output
ripple voltage. Decreasing its ESR reduces both output
resistance and ripple. Smaller capacitance values can
be used with light loads. Use the following equation to
calculate the peak-to-peak ripple:
Bypass the incoming supply to reduce its AC imped-
ance and the impact of the MAX1682/MAX1683’s
switching noise. When loaded, the circuit draws a con-
tinuous current of 2 x I
sufficient.
267
Table 3. Suggested Capacitor Values for
Minimum Size
MAX1682
MAX1683
V
PART
RIPPLE
= I
OUT
FREQUENCY
803-946-0690
714-969-2491
603-224-1961
803-946-0590
714-969-2491
(kHz)
/ (f
12
35
PHONE
OSC
OUT
Input Bypass Capacitor
x C2) + 2 x I
. A 0.1µF bypass capacitor is
Output Capacitor (C2)
CAPACITOR
VALUE (µF)
3.3
1
OUT
803-448-2170
714-960-6492
603-224-1430
803-626-3123
714-960-6492
x ESR
FAX
TYPICAL
R
OUT
35
35
C2
(Ω)