MAX829SNTR Просмотр технического описания (PDF) - ON Semiconductor
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MAX829SNTR Datasheet PDF : 12 Pages
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MAX828 MAX829
Capacitor Selection
In order to maintain the lowest output resistance and
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).
Table 1 shows various values of C1 and the corresponding
W output resistance values at +25°C. It assumes a 0.1 ESRC1
W and 0.5 RSW. Table 2 shows the output voltage ripple for
W various values of C2. The VRIPPLE values assume 10mA
output load current and 0.1 ESRC2.
Table 1. Output Resistance vs. C1 (ESR = 0.1Ω)
W W C1(µF) MAX828 ROUT ( ) MAX829 ROUT ( )
0.1
1.7k
580
1
170
61
3.3
55
21
10
21
10
47
8.0
5.7
100
6.2
5.1
W Table 2. Output Voltage Ripple vs. C2 (ESR = 0.1 ) IOUT
= 10mA
C2(µF) MAX828 VRIPPLE (mV) MAX829 VRIPPLE (mV)
1
830
290
3.3
250
87
10
83
28
47
17
6.1
100
8.3
2.9
Input Supply Bypassing
The VIN input should be capacitively bypassed to reduce
AC impedance and minimize noise effects due to the
switching internal to the device. The recommended
capacitor depends on the configuration of the MAX828/829.
If the device is loaded from OUT to GND it is
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 (0.1µF) capacitor from IN
to OUT is sufficient.
Voltage Inverter
The most common application for charge pump devices is
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 –VIN plus any
voltage drops due to loading. Refer to Table 1 and Table 2
for capacitor selection.
C3 +
Vin
3.3 mF*
C2
Vout
OUT
1
m C1+
5
3.3 F*
+
+
2 IN
C1
RL
3.3 mF*
3 C1–
GND
4
Voltage Inverter
m *10 F (MAX828)
Figure 3. Test Circuit
Cascading Devices
Two or more MAX828/829’s can be cascaded to increase
output voltage (Figure 4). If the output is lightly loaded, it
will be close to (- 2 x VIN) but will droop at least by ROUT of
the first device multiplied by the IQ of the second. It can be
seen that the output resistance rises rapidly for multiple
cascaded devices.
Vin+
3
2
C1
+
4
MAX828
MAX829
“1”
3
2
C1
+
4
MAX828
MAX829
“n”
Vout
5
1
5
1
C2
+
C2
+
Vout = –nVin
Figure 4. Cascading MAX828s or MAX829s to
Increase Output Voltage
Paralleling Devices
To reduce the value of ROUT, multiple MAX828/829s can
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.
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