19-0495; Rev 3; 9/99
Switched-Capacitor Voltage Inverters
General Description
The ultra-small MAX828/MAX829 monolithic, CMOS
charge-pump inverters accept input voltages ranging
from +1.5V to +5.5V. The MAX828 operates at 12kHz,
and the MAX829 operates at 35kHz. Their high efficiency
(greater than 90% over most of the load-current range)
and low operating current (60µA for the MAX828) make
these devices ideal for both battery-powered and board-
level voltage-conversion applications.
The MAX828/MAX829 combine low quiescent current
and high efficiency. Oscillator control circuitry and four
power MOSFET switches are included on-chip.
Applications include 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 a similar device with logic-controlled shutdown,
refer to the MAX1719/MAX1720/MAX1721. For applica-
tions requiring more power, the MAX860 delivers up to
50mA with a voltage drop of 600mV, in a space-saving
µMAX package.
o
5-Pin SOT23-5 Package
o
95% Voltage Conversion Efficiency
o
Inverts Input Supply Voltage
o
60µA Quiescent Current (MAX828)
o
+1.5V to +5.5V Input Voltage Range
o
Requires Only Two Capacitors
o
25mA Output Current
Features
MAX828/MAX829
Ordering Information
PART
MAX828EUK
MAX829EUK
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
PIN-
PACKAGE
5 SOT23-5
5 SOT23-5
SOT
TOP MARK
AABI
AABJ
Applications
Small LCD Panels
Cell Phones
Medical Instruments
Handy-Terminals, PDAs
Battery-Operated Equipment
Typical Operating Circuit
TOP VIEW
5
C1+
IN
2
INPUT
SUPPLY
VOLTAGE
OUT
1
Pin Configuration
MAX828
MAX829
3
C1-
OUT
4
1
NEGATIVE
OUTPUT
VOLTAGE
5
C1+
IN
2
MAX828
MAX829
4
GND
C1-
3
GND
SOT23-5
NEGATIVE VOLTAGE CONVERTER
________________________________________________________________
Maxim Integrated Products
1
For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Switched-Capacitor Voltage Inverters
MAX828/MAX829
ABSOLUTE MAXIMUM RATINGS
IN to GND .................................................................+6.0V, -0.3V
OUT to GND .............................................................-6.0V, +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
MAX828EUK/MAX829EUK ...............................-40°C to +85°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+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 = 10µF (MAX828), C1 = C2 = 3.3µF (MAX829), T
A
= 0°C to +85°C, unless otherwise noted. Typical values
are at T
A
= +25°C.)
PARAMETER
Supply Current
Minimum Supply Voltage
Maximum Supply Voltage
Oscillator Frequency
Power Efficiency
Voltage Conversion Efficiency
Output Resistance
T
A
= +25°C
R
LOAD
= 10kΩ
R
LOAD
= 10kΩ
T
A
= +25°C
R
LOAD
= 1kΩ, T
A
= +25°C
R
LOAD
=
∞
I
OUT
= 5mA
T
A
= +25°C
T
A
= 0°C to + 85°C
95
MAX828
MAX829
8.4
24.5
12
35
94
99.9
20
50
65
CONDITIONS
MAX828
MAX829
T
A
= +25°C
T
A
= 0°C to + 85°C
1.25
1.5
5.5
15.6
45.5
MIN
TYP
60
150
1.0
MAX
90
260
UNITS
µA
V
V
kHz
%
%
Ω
Note 1:
Capacitor contribution is approximately 20% of the output impedance [ESR + 1 / (pump frequency x capacitance)].
ELECTRICAL CHARACTERISTICS
(V
IN
= +5V, C1 = C2 = 10µF (MAX828), C1 = C2 = 3.3µF (MAX829), T
A
= -40°C to +85°C, unless otherwise noted. Typical values
are at T
A
= +25°C.) (Note 2)
PARAMETER
Supply Current
Supply Voltage Range
Oscillator Frequency
Output Resistance
MAX828
MAX829
R
LOAD
= 10kΩ
MAX828
MAX829
I
OUT
= 5mA
1.5
6
19
CONDITIONS
MIN
TYP
MAX
115
325
5.5
20
54.3
65
UNITS
µA
V
kHz
Ω
Note 2:
All -40°C to +85°C specifications above 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.)
OUTPUT RESISTANCE
vs. SUPPLY VOLTAGE
MAX828/829-01
MAX828/MAX829
OUTPUT RESISTANCE
vs. TEMPERATURE
MAX828/829-02
MAX828
OUTPUT CURRENT vs. CAPACITANCE
V
IN
= 4.75V, V
OUT
= -4.0V
40
OUTPUT CURRENT (mA)
35
30
25
20
15
10
5
0
V
IN
= 1.9V, V
OUT
= -1.5V
V
IN
= 3.15V, V
OUT
= -2.5V
MAX828/829-03
40
35
OUTPUT RESISTANCE (Ω)
30
25
20
15
10
5
0
1.5
2.5
3.5
4.5
MAX828
MAX829
50
45
OUTPUT RESISTANCE (Ω)
40
35
30
25
20
15
10
V
IN
= 5.0V
V
IN
= 3.3V
V
IN
= 1.5V
45
5.5
-40
-20
0
20
40
60
80
0
5
10 15 20 25 30 35 40 45 50
CAPACITANCE (µF)
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
MAX829
OUTPUT CURRENT vs. CAPACITANCE
MAX828/829-04
MAX828
OUTPUT VOLTAGE RIPPLE
vs. CAPACITANCE
MAX828/829-05
MAX829
OUTPUT VOLTAGE RIPPLE
vs. CAPACITANCE
OUTPUT VOLTAGE RIPPLE (mVp-p)
400
350
300
250
200
150
100
50
0
0
5
10
15
20
25
30
V
IN
= 4.75V, V
OUT
= -4.0V
V
IN
= 3.15V, V
OUT
= -2.5V
V
IN
= 1.9V, V
OUT
= -1.5V
MAX828/829-06
45
40
OUTPUT CURRENT (mA)
35
30
25
20
15
10
5
0
0
5
OUTPUT VOLTAGE RIPPLE (mVp-p)
V
IN
= 4.75V, V- = -4.0V
500
450
400
350
300
250
200
150
100
50
0
0
5
10
15
20
25
V
IN
= 4.75V, V
OUT
= -4.0V
V
IN
= 3.15V, V
OUT
= -2.5V
V
IN
= 1.9V, V
OUT
= -1.5V
450
V
IN
= 3.15V, V- = -2.5V
V
IN
= 1.9V, V- = -1.5V
10
15
20
25
30
30
CAPACITANCE (µF)
CAPACITANCE (µF)
CAPACITANCE (µF)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX828/829-07
MAX828
PUMP FREQUENCY vs. TEMPERATURE
55
PUMP FREQUENCY (kHz)
50
45
40
35
30
25
20
V
IN
= 3.3V
V
IN
= 5.0V
V
IN
= 1.5V
MAX828/829-08
MAX829
PUMP FREQUENCY vs. TEMPERATURE
MAX828/829-9
200
175
SUPPLY CURRENT (µA)
150
125
100
75
50
25
0
1.5
2.5
3.5
4.5
MAX828
MAX829
60
55
PUMP FREQUENCY (kHz)
50
V
IN
= 1.5V
45
40
V
IN
= 3.3V
V
IN
= 5.0V
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
35
15
10
5.5
-40
-20
0
20
40
60
80
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
30
_______________________________________________________________________________________
3
Switched-Capacitor Voltage Inverters
MAX828/MAX829
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
IN
= +5V, C1 = C2 = C3, T
A
= +25°C, unless otherwise noted.)
OUTPUT VOLTAGE
vs. OUTPUT CURRENT
MAX828/829-10
EFFICIENCY vs. OUTPUT CURRENT
90
80
EFFICIENCY (%)
70
60
50
40
30
20
V
IN
= 2.0V
V
IN
= 3.3V
V
IN
= 5.0V
MAX828/829-11
MAX828/829-13
0.5
-0.5
OUTPUT VOLTAGE (V)
V
IN
= 2.0V
-1.5
V
IN
= 3.3V
-2.5
-3.5
-4.5
-5.5
0
5
100
V
IN
= 5.0V
10
0
10 15 20 25 30 35 40 45 50
OUTPUT CURRENT (mA)
0
5
10 15 20 25 30 35 40 45 50
OUTPUT CURRENT (mA)
MAX828
OUTPUT NOISE AND RIPPLE
MAX828/829-12
MAX829
OUTPUT NOISE AND RIPPLE
V
OUT
20mV/div
V
OUT
20mV/div
20µs/div
V
IN
= 3.3V, V
OUT
= -3.2V, I
OUT
= 5mA, AC COUPLED
10µs/div
V
IN
= 3.3V, V
OUT
= -3.2V, I
OUT
= 5mA, 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
*10µF
(MAX828)
2
3
1
OUT
IN
MAX828
MAX829
C1-
GND
4
C3
3.3µF*
V
IN
1
2
3
4
5
V
OUT
C1+
5
C2
3.3µF*
C1
3.3µF*
R
L
VOLTAGE INVERTER
Figure 1. Test Circuit
4
_______________________________________________________________________________________
Switched-Capacitor Voltage Inverters
_______________Detailed Description
The MAX828/MAX829 capacitive charge pumps invert the
voltage applied to their input. For highest performance,
use low equivalent series resistance (ESR) capacitors.
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
MAX828/MAX829
C2
S3
S4
V
OUT
= -(V
IN
)
Charge-Pump Output
The MAX828/MAX829 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
where the output impedance is roughly approximated
by:
1
R
OUT
≅
+
2R
+
4ESR
C1
+
ESR
C2
(
f
OSC
)
x C1
SW
The first term is the effective resistance of an ideal
switched-capacitor circuit (Figures 3a and 3b), and
R
SW
is the sum of the charge pump’s internal switch
resistances (typically 8Ω to 9Ω at V
IN
= +5V). The typical
output impedance is more accurately determined from
the
Typical Operating Characteristics.
Efficiency Considerations
The efficiency of the MAX828/MAX829 is dominated by
its quiescent supply current (I
Q
) at low output current
and by its output impedance (R
OUT
) at higher output
current; it is given by:
η≅
I
OUT
I
OUT
x R
OUT
1
−
I
OUT
+
I
Q
V
IN
Applications Information
Capacitor Selection
To maintain the lowest output resistance, use capacitors
with low ESR (Table 1). The charge-pump output resis-
tance is a function of C1’s and C2’s ESR. Therefore,
minimizing the charge-pump capacitor’s ESR minimizes
the total output resistance.
f
V+
V
OUT
V+
R
EQUIV
V
OUT
R
EQUIV
=
1
f
×
C1
C2
C1
C2
R
L
R
L
Figure 3a. Switched-Capacitor Model
Figure 3b. Equivalent Circuit
5
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