19-1240; Rev 0; 6/97
Switched-Capacitor Voltage Inverters
_______________General Description
The ultra-small MAX870/MAX871 monolithic, CMOS
charge-pump inverters accept input voltages ranging
from +1.4V to +5.5V. The MAX870 operates at 125kHz,
and the MAX871 operates at 500kHz. Their high efficien-
cy (90%) and low operating current (0.7mA for the
MAX870) make these devices ideal for both battery-pow-
ered and board-level voltage-conversion applications.
Oscillator control circuitry and four power MOSFET
switches are included on-chip. A typical MAX870/
MAX871 application is generating a -5V supply from a
+5V logic supply to power analog circuitry. Both parts
come in a 5-pin SOT23-5 package and can deliver 25mA
with a voltage drop of 500mV.
For applications requiring more power, the MAX860
delivers up to 50mA with a voltage drop of 600mV, in a
space-saving µMAX package.
____________________________Features
o
5-Pin SOT23-5 Package
o
99% Voltage Conversion Efficiency
o
Invert Input Supply Voltage
o
0.7mA Quiescent Current (MAX870)
o
+1.4V to +5.5V Input Voltage Range
o
Require Only Two Capacitors
o
25mA Output Current
o
Shutdown Control
MAX870/MAX871
______________Ordering Information
PART
MAX870C/D
MAX870EUK
MAX871C/D
MAX871EUK
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
PIN-
PACKAGE
Dice*
5 SOT23-5
Dice*
5 SOT23-5
SOT
TOP MARK
—
ABZN
—
ABZO
________________________Applications
Local -5V Supply from 5V Logic Supply
Small LCD Panels
Cell Phones
Medical Instruments
Handy-Terminals, PDAs
Battery-Operated Equipment
*
Dice are tested at T
A
= +25°C.
__________Typical Operating Circuit
__________________Pin Configuration
5
C1+
IN
2
INPUT
SUPPLY
VOLTAGE
TOP VIEW
MAX870
MAX871
3
C1-
OUT
4
1
NEGATIVE
OUTPUT
VOLTAGE
OUT
1
5
C1+
IN
2
MAX870
MAX871
4
GND
C1-
3
GND
SOT23-5
NEGATIVE VOLTAGE CONVERTER
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
Switched-Capacitor Voltage Inverters
MAX870/MAX871
ABSOLUTE MAXIMUM RATINGS
IN to GND ..............................................................+6.0V to -0.3V
OUT to GND ..........................................................-6.0V to +0.3V
C1+ ..............................................................(V
IN
+ 0.3V) to -0.3V
C1-............................................................(V
OUT
- 0.3V) to +0.3V
OUT Output Current ...........................................................50mA
OUT Short Circuit to GND .............................................Indefinite
Continuous Power Dissipation (T
A
= +70°C)
SOT23-5 (derate 7.1mW/°C above +70°C)...................571mW
Operating Temperature Range
MAX870EUK/MAX871EUK ...............................-40°C to +85°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
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.
ELECTRICAL CHARACTERISTICS
(V
IN
= +5V, C1 = C2 = 1µF (MAX870), C1 = C2 = 0.33µF (MAX871),
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values
are at T
A
= +25°C.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Current
Minimum Supply Voltage
Maximum Supply Voltage
Oscillator Frequency
Power Efficiency
Voltage Conversion Efficiency
T
A
= +25°C
R
LOAD
= 10kΩ
R
LOAD
= 10kΩ
T
A
= +25°C
R
LOAD
= 500kΩ,
T
A
=+25°C
R
LOAD
=
∞,
T
A
=+25°C
MAX870
MAX871
MAX870
MAX871
MAX870
MAX871
C1 = C2 = 1µF
C1 = C2 = 0.47µF
C1 = C2 = 0.33µF
MAX871
C1 = C2 = 0.22µF
C1 = C2 = 0.1µF
T
A
= 0°C to + 85°C
98
96
81
325
125
500
90
75
99.3
99
20
25
20
25
35
65
50
Ω
50
MAX870
MAX871
T
A
= +25°C
T
A
= 0°C to + 85°C
1.4
1.5
5.5
169
675
0.7
2.7
1.0
1.0
3.8
mA
V
V
kHz
%
%
MAX870
Output Resistance (Note 1)
I
OUT
= T
A
= +25°C
5mA
Note 1:
Capacitor contribution is approximately 20% of the output impedance [ESR + 1 / (pump frequency x capacitance)].
ELECTRICAL CHARACTERISTICS
(V
IN
= +5V, C1 = C2 = 1µF (MAX870), C1 = C2 = 0.33µF (MAX871),
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 2)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Current
Minimum Supply-Voltage Range
Maximum Supply-Voltage Range
Oscillator Frequency
Output Resistance
Voltage Conversion Efficiency
MAX870
MAX871
R
LOAD
= 10kΩ
R
LOAD
= 10kΩ
MAX870
MAX871
I
OUT
= 5mA
R
LOAD
=
∞
MAX870
MAX871
97
95
56
225
1.6
5.5
194
775
65
1.3
4.4
mA
V
V
kHz
Ω
%
Note 2:
All -40°C to +85°C specifications are guaranteed by design.
2
_______________________________________________________________________________________
Switched-Capacitor Voltage Inverters
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1, V
IN
= +5V, C1 = C2 = C3, T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX870/71-TOC01
MAX870/MAX871
OUTPUT RESISTANCE
vs. SUPPLY VOLTAGE
MAX828/829-02
MAX870
OUTPUT RESISTANCE vs. TEMPERATURE
45
OUTPUT RESISTANCE (Ω)
40
35
30
25
20
15
10
5
V
IN
= 5.0V
V
IN
= 3.3V
V
IN
= 1.5V
MAX870/71 ROC3
3.0
2.5
SUPPLY CURRENT (mA)
2.0
1.5
1.0
MAX870
0.5
0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
MAX871
60
50
OUTPUT RESISTANCE (Ω)
50
40
MAX871
30
MAX870
20
10
5.5
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
0
-40
-15
10
35
60
85
TEMPERATURE (°C)
MAX870
OUTPUT CURRENT vs. CAPACITANCE
40
OUTPUT CURRENT (mA)
35
30
25
20
15
10
5
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
CAPACITANCE (µF)
V
IN
= 1.9V, V
OUT
= -1.5V
V
IN
= 3.15V, V
OUT
= -2.5V
V
IN
= 4.75V, V
OUT
= -4.0V
MAX870/871-04
MAX870
OUTPUT VOLTAGE RIPPLE
vs. CAPACITANCE
400
350
300
250
200
150
100
50
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
CAPACITANCE (µF)
10
0
V
IN
= 4.75V, V
OUT
= -4.0V
V
IN
= 3.15V, V
OUT
= -2.5V
V
IN
= 1.9V, V
OUT
= -1.5V
MAX870/871-05
MAX871
OUTPUT RESISTANCE vs. TEMPERATURE
MAX870/71-TOC06
45
450
OUTPUT VOLTAGE RIPPLE (mVp-p)
70
60
OUTPUT RESISTANCE (Ω)
V
IN
= 1.5V
50
40
V
IN
= 3.3V
30
20
V
IN
= 5.0V
-40
-15
10
35
60
85
TEMPERATURE (°C)
MAX871
OUTPUT CURRENT vs. CAPACITANCE
MAX870/871-07
MAX871
OUTPUT VOLTAGE RIPPLE
vs. CAPACITANCE
MAX870/71 TOC08
MAX870
OUTPUT VOLTAGE
vs. OUTPUT CURRENT
-0.5
-1.0
OUTPUT VOLTAGE (V)
-1.5
-2.0
-2.5
-3.0
-3.5
-4.0
-4.5
-5.0
V
IN
= 5.0V
V
IN
= 3.3V
V
IN
= 2.0V
MAX870/871-TOC9
35
30
OUTPUT CURRENT (mA)
25
20
15
10
5
0
0
500
450
OUTPUT VOLTAGE RIPPLE (mVp-p)
400
350
300
250
200
150
100
50
0
V
IN
= 3.15V, V
OUT
= -2.5V
V
IN
= 1.9V, V
OUT
= -1.5V
V
IN
= 4.75V, V
OUT
= -4.0V
0
V
IN
= 4.75V, V
OUT
= -4.0V
V
IN
= 3.15V, V
OUT
= -2.5V
V
IN
= 1.9V, V
OUT
= -1.5V
0.5
1.0
1.5
2.0
2.5
0
0.5
1.0
1.5
2.0
2.5
0
5
10
15
20
25
30
35
40
45
CAPACITANCE (µF)
CAPACITANCE (µF)
OUTPUT CURRENT (mA)
_______________________________________________________________________________________
3
Switched-Capacitor Voltage Inverters
MAX870/MAX871
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
IN
= +5V, C1 = C2 = C3, T
A
= +25°C, unless otherwise noted.)
MAX870
EFFICIENCY vs. OUTPUT CURRENT
MAX870/71-TOC10
MAX871
EFFICIENCY vs. OUTPUT CURRENT
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
V
IN
= 2.0V
V
IN
= 3.3V
V
IN
= 5.0V
MAX870/71 TOC11
PUMP FREQUENCY vs. TEMPERATURE
550
500
PUMP FREQUENCY (kHz)
450
400
350
300
250
200
150
100
V
IN
= 1.5V, MAX870
V
IN
= 3.3V OR 5.0V, MAX870
V
IN
= 1.5V, MAX871
V
IN
= 3.3V OR 5.0V, MAX871
MAX870/71-TOC12
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0
5
V
IN
= 2.0V
V
IN
= 3.3V
V
IN
= 5.0V
90
600
10 15 20 25 30 35 40 45 50
OUTPUT CURRENT (mA)
0
5
10
15
20
25
30
35
40
-40
-15
10
35
60
85
OUTPUT CURRENT (mA)
TEMPERATURE (°C)
MAX870
OUTPUT NOISE AND RIPPLE
MAX870/71-TCC13
MAX871
OUTPUT NOISE AND RIPPLE
MAX870/71-TCC14
2µs/div
V
IN
= 3.3V, V
OUT
= -3.18V, I
OUT
= 5mA,
20mV/div, AC COUPLED
1µs/div
V
IN
= 3.3V, V
OUT
= -3.14V, I
OUT
= 5mA,
20mV/div, AC COUPLED
_____________________Pin Description
PIN
NAME
OUT
IN
C1-
GND
C1+
FUNCTION
Inverting Charge-Pump Output
Positive Power-Supply Input
Flying Capacitor’s Negative Terminal
Ground
Flying Capacitor’s Positive Terminal
*1µF
(MAX870)
2
3
1
OUT
IN
MAX870
MAX871
C1-
GND
4
C3
0.33µF*
R
L
V
IN
1
2
3
4
5
V
OUT
C1+
5
C2
0.33µF*
C1
0.33µF*
VOLTAGE INVERTER
Figure 1. Test Circuit
4
_______________________________________________________________________________________
Switched-Capacitor Voltage Inverters
_______________Detailed Description
The MAX870/MAX871 capacitive charge pumps invert
the voltage applied to their input. For highest perfor-
mance, use low equivalent series resistance (ESR)
capacitors (e.g., ceramic).
During the first half-cycle, switches S2 and S4 open,
switches S1 and S3 close, and capacitor C1 charges to
the voltage at IN (Figure 2). During the second half-
cycle, S1 and S3 open, S2 and S4 close, and C1 is level
shifted downward by V
IN
volts. This connects C1 in par-
allel with the reservoir capacitor C2. If the voltage across
C2 is smaller than the voltage across C1, then charge
flows from C1 to C2 until the voltage across C2 reaches
-V
IN
. The actual voltage at the output is more positive
than -V
IN
, since switches S1–S4 have resistance and the
load drains charge from C2.
S1
IN
C1
S2
MAX870/MAX871
C2
S3
S4
V
OUT
= -(V
IN
)
Charge-Pump Output
The MAX870/MAX871 are not voltage regulators: the
charge pump’s output source resistance is approxi-
mately 20Ω at room temperature (with V
IN
= +5V), and
V
OUT
approaches -5V when lightly loaded. V
OUT
will
droop toward GND as load current increases. The
droop of the negative supply (V
DROOP-
) equals the cur-
rent draw from OUT (I
OUT
) times the negative convert-
er’s source resistance (RS-):
V
DROOP-
= I
OUT
x RS-
The negative output voltage will be:
V
OUT
= -(V
IN
– V
DROOP-
)
Figure 2. Ideal Voltage Inverter
The internal losses are associated with the IC’s internal
functions, such as driving the switches, oscillator, etc.
These losses are affected by operating conditions such
as input voltage, temperature, and frequency.
The next two losses are associated with the voltage
converter circuit’s output resistance. Switch losses
occur because of the on-resistance of the MOSFET
switches in the IC. Charge-pump capacitor losses
occur because of their ESR. The relationship between
these losses and the output resistance is as follows:
P
PUMP CAPACITOR LOSSES
+P
CONVERSION LOSSES
= I
OUT
x R
OUT
1
R
OUT
≅
+
2R
SWITCHES
+
4ESR
C1
+
ESR
C2
f
OSC
x C1
2
Efficiency Considerations
The power efficiency of a switched-capacitor voltage
converter is affected by three factors: the internal loss-
es in the converter IC, the resistive losses of the pump
capacitors, and the conversion losses during charge
transfer between the capacitors. The total power loss is:
ΣP
LOSS
= P
INTERNAL LOSSES
+ P
SWITCH LOSSES
+ P
PUMP CAPACITOR LOSSES
+ P
CONVERSION LOSSES
f
V+
V
OUT
(
)
where f
OSC
is the oscillator frequency. The first term is
the effective resistance from an ideal switched-
capacitor circuit. See Figures 3a and 3b.
R
EQUIV
V+
1
R
EQUIV
=
f
×
C1
C2
V
OUT
R
L
C1
C2
R
L
Figure 3a. Switched-Capacitor Model
Figure 3b. Equivalent Circuit
5
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