MAX680CSA ,+5V to 10V Voltage ConvertersFeaturesThe MAX680/MAX681 are monolithic, CMOS, dual' 95% Voltage-Conversion Efficiencycharge-pump ..
MAX680CSA ,+5V to 10V Voltage Convertersapplications includeMAX681CPD 0°C to +70°C 14 Plastic DIPgenerating ±6V from a 3V battery and gener ..
MAX680CSA ,+5V to 10V Voltage ConvertersGeneral Description ________
MAX680CSA ,+5V to 10V Voltage ConvertersMAX680/MAX68119-0896; Rev 1; 7/96+5V to ±10V Voltage Converters ________________
MAX680CSA+ ,+5V to ±10V Voltage Convertersapplications that need both positive and_______________Ordering Informationnegative voltages genera ..
MAX680CSA+ ,+5V to ±10V Voltage Convertersapplications include: ±6V from 3V Lithium Cell Battery-OperatedEquipment_________Typical Operating ..
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MAX680CPA-MAX680CSA-MAX680ESA-MAX681CPD-MAX681EPD
+5V to 10V Voltage Converters
________________General DescriptionThe MAX680/MAX681 are monolithic, CMOS, dual
charge-pump voltage converters that provide ±10V out-
puts from a +5V input voltage. The MAX680/MAX681 pro-
vide both a positive step-up charge pump to develop
+10V from +5V input and an inverting charge pump to
generate the -10V output. Both parts have an on-chip,
8kHz oscillator. The MAX681 has the capacitors internal to
the package, and the MAX680 requires four external
capacitors to produce both positive and negative voltages
from a single supply.
The output source impedances are typically 150Ω, pro-
viding useful output currents up to 10mA. The low quies-
cent current and high efficiency make this device suitable
for a variety of applications that need both positive and
negative voltages generated from a single supply.
The MAX864/MAX865 are also recommended for new
designs. The MAX864 operates at up to 200kHz and uses
smaller capacitors. The MAX865 comes in the smaller
µMAX package.
________________________ApplicationsThe MAX680/MAX681 can be used wherever a single
positive supply is available and where positive and nega-
tive voltages are required. Common applications include
generating ±6V from a 3V battery and generating ±10V
from the standard +5V logic supply (for use with analog
circuitry). Typical applications include:
____________________________Features95% Voltage-Conversion Efficiency85% Power-Conversion Efficiency+2V to +6V Voltage RangeOnly Four External Capacitors Required (MAX680)No Capacitors Required (MAX681)500µA Supply CurrentMonolithic CMOS Design
MAX680/MAX681
+5V to ±10V Voltage Converters
_________Typical Operating Circuits_________________Pin Configurations19-0896; Rev 1; 7/96
±6V from 3V Lithium Cell
Hand-Held Instruments
Data-Acquisition Systems
Panel Meters
±10V from +5V Logic
Supply
Battery-Operated
Equipment
Operational Amplifier
Power Supplies
MAX680/MAX681
+5V to ±10V Voltage Converters
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VCC= +5V, test circuit Figure 1, TA= +25°C, unless otherwise noted.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
VCC...................................................................................+6.2V
V+ ......................................................................................+12V
V- ..........................................................................................-12V
V- Short-Circuit Duration ...........................................Continuous
V+ Current ..........................................................................75mA
VCC ΔV/ΔT ..........................................................................1V/µs
Continuous Power Dissipation (TA = +70°C)
8-Pin Plastic DIP (derate 9.09mW/°C above +70°C) .....727mW
8-Pin Narrow SO (derate 5.88mW/°C above +70°C) .....471mW
8-Pin CERDIP (derate 8.00mW/°C above +70°C) ..........640mW
14-Pin Plastic DIP (derate 10.00mW/°C above +70°C) ...800mW
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
MAX680/MAX681
+5V to ±10V Voltage Converters(V)
LOADCURRENT(A)(V)12346789
OUTPUT VOLTAGE vs. OUTPUT CURRENT
(FROM V+ TO V-)MAX680/681-TOC4
OUTPUT CURRENT (mA)
|VOUT
| (V)
OUTPUT SOURCE RESISTANCE
vs. TEMPERATURE
MAX680/681-TOC5
TEMPERATURE (°C)
OUTPUT SOURCE RESISTANCE (
OUTPUT RIPPLE vs.
OUTPUT CURRENT (IL+ OR IL-)
MAX681/681-TOC6
OUTPUT CURRENT (mA)
OUTPUT RIPPLE (mVp-p)50
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MAX680/MAX681
+5V to ±10V Voltage Converters
_______________Detailed DescriptionThe MAX681 contains all circuitry needed to implement
a dual charge pump. The MAX680 needs only four
capacitors. These may be inexpensive electrolytic
capacitors with values in the 1µF to 100µF range. The
MAX681 contains two 1.5µF capacitors as C1 and C2,
and two 2.2µF capacitors as C3 and C4. SeeTypical
Operating Characteristics.
Figure 2a shows the idealized operation of the positive
voltage converter. The on-chip oscillator generates a
50% duty-cycle clock signal. During the first half of the
cycle, switches S2 and S4 are open, S1 and S3 are
closed, and capacitor C1 is charged to the input volt-
age VCC. During the second half-cycle, S1 and S3 are
open, S2 and S4 are closed, and C1 is translated
upward by VCCvolts. Assuming ideal switches and no
load on C3, charge is transferred onto C3 from C1 such
that the voltage on C3 will be 2VCC, generating the
positive supply.
Figure 2b shows the negative converter. The switches
of the negative converter are out of phase from the pos-
itive converter. During the second half of the clock
cycle, S6 and S8 are open and S5 and S7 are closed,
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 ConsiderationsTheoretically, a charge-pump voltage multiplier can
approach 100% efficiency under the following con-
ditions: The charge-pump switches have virtually no offset
and extremely low on-resistance Minimal power is consumed by the drive circuitry The impedances of the reservoir and pump capaci-
tors are negligible
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:
LOSSTOT =LOSSPOS+ LOSSNEG1⁄2C1[(V+)2– (V+)(VCC)] +⁄2C2[(V+)2– (V-)2]
There will be a substantial voltage difference between
(V+ - VCC) and VCCfor the positive pump, and
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.
________Maximum Operating LimitsThe MAX680/MAX681 have on-chip zener diodes that
clamp VCCto approximately 6.2V, V+ to 12.4V, and
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.
________________________Applications
Positive and Negative ConverterThe 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.
MAX680/MAX681
+5V to ±10V Voltage Converters
MAX680/MAX681The MAX680/MAX681 are
notvoltage regulators: the
output source resistance of either charge pump is
approximately 150Ωat room temperature with VCCat
5V. Under light load with an input VCCof 5V, V+ will
approach +10V and V- will be at -10V. However both,
V+ and V- will droop toward GND as the current drawn
from eitherV+ or V- increases, since the negative con-
verter draws its power from the positive converter’s out-
put. To predict output voltages, treat the chips as two
separate converters and analyze them separately. First,
the droop of the negative supply (VDROP-) equals the
current drawn from V- - (IL-) times the source resistance
of the negative converter (RS-):
VDROP-= IL-x RS-
Likewise, the positive supply droop (VDROP+) equals
the current drawn from the positive supply (IL+) times
the positive converter’s source resistance (RS+),
except that the current drawn from the positive supply
is the sum of the current drawn by the load on the posi-
tive supply (IL+) plus the current drawn by the negative
converter (IL-):
(VDROP+) = IL+ x RS+ = (IL+ + IL-) x RS+
The positive output voltage will be:
V+ = 2VCC – VDROP+
The negative output voltage will be:
V- = (V+ - VDROP) = - (2VCC - VDROP + - VDROP-)
The positive and negative charge pumps are tested
and specified separately to provide the separate values
of output source resistance for use in the above formu-
las. When the positive charge pump is tested, the neg-
ative charge pump is unloaded. When the negative
charge pump is tested, the positive supply V+ is from
an external source, isolating the negative charge
pump.
Calculate the ripple voltage on either output by noting
that the current drawn from the output is supplied by
the reservoir capacitor alone during one half-cycle of
the clock. This results in a ripple of:
VRIPPLE= 1⁄2IOUT (1⁄ fPUMP)(1⁄ CR)
For the nominal fPUMPof 8kHz with 10µF reservoir
capacitors, the ripple will be 30mV with IOUTat 5mA.
Remember that in most applications, the positive
charge pump’s IOUTis the load current plusthe current
taken by the negative charge pump.
+5V to ±10V Voltage ConvertersFigure 4. Paralleling MAX680s For Lower Source Resistance
