MAX828 ON, MAX828 Datasheet - Page 4

• Manufacturer Part Number: MAX828
• Description: Switched Capacitor Voltage Converters
• Manufacturer: ON

Capacitor Selection
output ripple voltage, it is recommended that low ESR
capacitors be used. Additionally, larger values of C1 will
lower the output resistance and larger values of C2 will
reduce output ripple. (See Equation 3).
output resistance values at +25 C. It assumes a 0.1
and 0.5
various values of C2. The V
output load current and 0.1
Table 1. Output Resistance vs. C1 (ESR = 0.1 )
Table 2. Output Voltage Ripple vs. C2 (ESR = 0.1
= 10mA
Input Supply Bypassing
AC impedance and minimize noise effects due to the
switching internal to the device.
capacitor depends on the configuration of the MAX828/829.
recommended that a large value capacitor (at least equal to
C1) be connected from the input to GND. If the device is
loaded from IN to OUT a small (0.1 F) capacitor from IN
to OUT is sufficient.
Voltage Inverter
the inverter (Figure 3). This application uses two external
capacitors - C1 and C2 (plus a power supply bypass
capacitor, if necessary). The output is equal to –V
voltage drops due to loading. Refer to Table 1 and Table 2
for capacitor selection.
C1( F)
C2( F)
In order to maintain the lowest output resistance and
Table 1 shows various values of C1 and the corresponding
The V
If the device is loaded from OUT to GND it is
The most common application for charge pump devices is
100
100
0.1
3.3
3.3
10
47
10
47
1
1
W
IN
R
MAX828 R
MAX828 V
input should be capacitively bypassed to reduce
SW
. Table 2 shows the output voltage ripple for
1.7k
170
8.0
6.2
55
21
830
250
8.3
83
17
RIPPLE
OUT
(
W
(mV) MAX829 V
W
)
ESR
RIPPLE
MAX829 R
C2
.
values assume 10mA
The recommended
580
5.7
5.1
61
21
10
290
6.1
2.9
87
28
RIPPLE
OUT
(
W
IN
(mV)
W
)
MAX828 MAX829
plus any
W
http://onsemi.com
ESR
) I
OUT
C1
4
Cascading Devices
output voltage (Figure 4). If the output is lightly loaded, it
will be close to (- 2 x V
the first device multiplied by the I
seen that the output resistance rises rapidly for multiple
cascaded devices.
Paralleling Devices
be connected in parallel (Figure 5). The output resistance
will be reduced by a factor of N where N is the number of
MAX828/829’s. Each device will require it’s own pump
capacitor (C1), but all devices may share one reservoir
capacitor (C2). However, to preserve ripple performance the
value of C2 should be scaled according to the number of
paralleled MAX828/829’s.
Two or more MAX828/829’s can be cascaded to increase
To reduce the value of R
+
Figure 4. Cascading MAX828s or MAX829s to
C1
1
2
3
3
4
5
OUT
IN
C1 –
Voltage Inverter
MAX828
MAX829
“1”
Increase Output Voltage
Figure 3. Test Circuit
GND
C1 +
3.3
C2
2
1
IN
m
C3
) but will droop at least by R
F*
5
4
OUT
+
+
V in +
, multiple MAX828/829s can
+
C1
3.3
+
C2
3.3
C1
V out = –nV in
m
3
4
5
m
Q
F*
F*
*10
of the second. It can be
+
MAX828
MAX829
m
F (MAX828)
“n”
V in
R L
C2
2
1
V out
V out
+
OUT
of