MAX680ESA Maxim Integrated Products, MAX680ESA Datasheet - Page 5

• Manufacturer Part Number: MAX680ESA
• Description: Charge Pumps 5V to +/-10V Voltage Converter
• Manufacturer: Maxim Integrated Products

Specifications of MAX680ESA

• Function: Inverting, Step Up
• Output Voltage: +/- 10 V
• Output Current: 10 mA
• Maximum Operating Temperature: + 85 C
• Package / Case: SOIC-8 Narrow
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT

cycle, S5 and S7 are open, S6 and S8 are closed, and
the charge on C2 is transferred to C4, generating the
negative supply. The eight switches are CMOS power
MOSFETs. S1, S2, S4, and S5 are P-channel
switches, while S3, S6, S7, and S8 are N-channel
switches.
__________Efficiency Considerations
Theoretically, a charge-pump voltage multiplier can
approach 100% efficiency under the following con-
ditions:
• The charge-pump switches have virtually no offset
• Minimal power is consumed by the drive circuitry
• The impedances of the reservoir and pump capaci-
For the MAX680/MAX681, the energy loss per clock
cycle is the sum of the energy loss in the positive and
negative converters as below:
There will be a substantial voltage difference between
(V+ - V
between V+ and V-, if the impedances of pump capaci-
tors C1 and C2 are high relative to their respective out-
put loads.
Larger C3 and C4 reservoir capacitor values reduce
output ripple. Larger values of both pump and reservoir
capacitors improve efficiency.
The MAX680/MAX681 have on-chip zener diodes that
clamp V
V- to -12.4V. Never exceed the maximum supply volt-
age: excessive current may be shunted by these
diodes, potentially damaging the chip. The MAX680/
MAX681 operate over the entire operating temperature
range with an input voltage of +2V to +6V.
________Maximum Operating Limits
and extremely low on-resistance
tors are negligible
CC
CC
LOSS
) and V
to approximately 6.2V, V+ to 12.4V, and
TOT
_______________________________________________________________________________________
=
= LOSS
CC
1
1
⁄
⁄
2
2
for the positive pump, and
C1
C2
POS
[
[
(V+)
(V+)
+ LOSS
2
2
– (V+)(V
– (V-)
+5V to ±10V Voltage Converters
NEG
2
]
CC
)
] +
________________________Applications
The most common application of the MAX680/MAX681
is as a dual charge-pump voltage converter that pro-
vides positive and negative outputs of two times a posi-
tive input voltage. For applications where PC board
space is at a premium, the MAX681, with its capacitors
internal to the package, offers the smallest footprint.
The simple circuit shown in Figure 3 performs the same
function using the MAX680 with external capacitors C1
and C3 for the positive pump and C2 and C4 for the
negative pump. In most applications, all four capacitors
are low-cost, 10µF or 22µF polarized electrolytics.
When using the MAX680 for low-current applications,
1µF can be used for C1 and C2 charge-pump capaci-
tors, and 4.7µF for C3 and C4 reservoir capacitors.
C1 and C3 must be rated at 6V or greater, and C2 and
C4 must be rated at 12V or greater.
Figure 3. Positive and Negative Converter
22 F
22 F
C2
C1
1
2
3
4
C1-
C2+
C2-
Positive and Negative Converter
V-
MAX680
GND
C1+
V
V+
CC
8
7
6
5
C4
22 F
C3
22 F
V+ OUT
V
GND
V- OUT
CC
IN
5