MAX1720 ON Semiconductor, MAX1720 Datasheet - Page 6

• Manufacturer Part Number: MAX1720
• Description: Switched Capacitor Voltage Inverter
• Manufacturer: ON Semiconductor

Capacitor Selection
output ripple voltage, it is recommended that low ESR
capacitors be used. Additionally, larger values of C
lower the output resistance and larger values of C
reduce output voltage ripple. (See Equation 3).
corresponding output resistance values at 25°C. Table 2
shows the output voltage ripple for various values of C
and C
calculated.
Input Supply Bypassing
reduce AC impedance and minimize noise effects due to the
switching internals in the device. If the device is loaded from
V
(at least equal to C
device is loaded from V
between the pins is sufficient.
out
In order to maintain the lowest output resistance and
Table 1 shows various values of C
The input voltage, V
Table 2. Output Voltage Ripple vs. Capacitance
to GND, it is recommended that a large value capacitor
Table 1. Output Resistance vs. Capacitance
(C
(C
3
. The data in Tables 1 and 2 was measured not
1
1
C
C
= C
= C
1
1
= C
= C
(mF)
(mF)
0.7
1.4
3.3
7.3
0.7
1.4
3.3
7.3
10
24
50
10
24
50
2
2
2
2
= C
= C
= C
= C
1
3
3
3
3
) be connected from V
), V
), V
in
in
in
in
should be capacitively bypassed to
= 4.75 V and V
= 4.75 V and V
to V
out
, a small (0.7 mF) capacitor
Output Voltage Ripple
1
, C
out
out
2
129.1
(mV)
R
69.5
37.0
26.5
25.9
24.1
in
382
342
255
164
132
(W)
and C
24
59
38
out
= −4.0 V
= −4.0 V
to GND. If the
3
with the
http://onsemi.com
2
1
1
will
will
, C
MAX1720
2
6
Voltage Inverter
voltage inverter (Figure 14). This application uses two or
three external capacitors. The C
(output capacitor) are required. The input bypass capacitor,
C
output is equal to −V
Refer to Tables 1 and 2 for capacitor selection. The test setup
used for the majority of the characterization is shown in
Figure 14.
Layout Considerations
practice is recommended. Mount components as close
together as possible to minimize stray inductance and
capacitance. Also, use a large ground plane to minimize noise
leakage into other circuitry.
Capacitor Resources
loss. Low ESR capacitors are recommended. The MAX1720
was characterized using the capacitors listed in Table 3. This
list identifies low ESR capacitors for the voltage inverter
application.
3
The most common application for a charge pump is the
As with any switching power supply circuit, good layout
Selecting the proper type of capacitor can reduce switching
Manufacturer/Contact
AVX
843−448−9411
www.avxcorp.com
Cornell Dubilier
508−996−8561
www.cornell−dubilier.com
Sanyo/Os−con
619−661−6835
www.sanyovideo.com/oscon.htm
Vishay
603−224−1961
www.vishay.com
, may be necessary depending on the application. The
−V
V
out
in
Table 3. Capacitor Types
+
+
in
plus any voltage drops due to loading.
Figure 18. Voltage Inverter
Capacitors = 10 mF
1
2
3
1
OSC
(pump capacitor) and C
Part Types/Series
ESRD
593D
TPS
SVP
6
5
4
594
SN
+
2