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19-0495; Rev 2; 4/97
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 (60A for the MAX828) make these devices ideal for both battery-powered and boardlevel 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 applications requiring more power, the MAX860 delivers up to 50mA with a voltage drop of 600mV, in a space-saving MAX package.
____________________________Features
o 5-Pin SOT23-5 Package o 95% Voltage Conversion Efficiency o Inverts Input Supply Voltage o 60A Quiescent Current (MAX828) o +1.5V to +5.5V Input Voltage Range o Requires Only Two Capacitors o 25mA Output Current
MAX828/MAX829
______________Ordering Information
PART MAX828C/D MAX828EUK MAX829C/D MAX829EUK TEMP. RANGE 0C to +70C -40C to +85C 0C to +70C -40C to +85C PINPACKAGE Dice* 5 SOT23-5 Dice* 5 SOT23-5 SOT TOP MARK -- AABI -- AABJ
________________________Applications
Small LCD Panels Cell Phones Medical Instruments Handy-Terminals, PDAs Battery-Operated Equipment
* Dice are tested at TA = +25C.
__________Typical Operating Circuit
__________________Pin Configuration
TOP VIEW
5
C1+
IN
2
INPUT SUPPLY VOLTAGE OUT 1 5 C1+
MAX828 MAX829
3 C1OUT 4 1 NEGATIVE OUTPUT VOLTAGE
IN
2
MAX828 MAX829
4 GND
C1-
3
GND
SOT23-5
NEGATIVE VOLTAGE CONVERTER
________________________________________________________________ Maxim Integrated Products
1
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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 (TA = +70C) SOT23-5 (derate 7.1mW/C above +70C)...................571mW Operating Temperature Range MAX828EUK/MAX829EUK ...............................-40C to +85C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C
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
(VIN = +5V, C1 = C2 = 10F (MAX828), C1 = C2 = 3.3F (MAX829), TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Supply Current Minimum Supply Voltage Maximum Supply Voltage Oscillator Frequency Power Efficiency Voltage Conversion Efficiency Output Resistance TA = +25C RLOAD = 10k RLOAD = 10k TA = +25C RLOAD = 10k, TA = +25C RLOAD = IOUT = 5mA TA = +25C TA = 0C to + 85C 95 MAX828 MAX829 8.4 24.5 12 35 98 99.9 20 50 65 CONDITIONS MAX828 MAX829 TA = +25C TA = 0C to + 85C 1.25 1.5 5.5 15.6 45.5 MIN TYP 60 150 1.0 MAX 90 260 UNITS A V V kHz % %
Note 1: Capacitor contribution is approximately 20% of the output impedance [ESR + 1 / (pump frequency x capacitance)].
ELECTRICAL CHARACTERISTICS
(VIN = +5V, C1 = C2 = 10F (MAX828), C1 = C2 = 3.3F (MAX829), TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2) PARAMETER Supply Current Supply Voltage Range Oscillator Frequency Output Resistance MAX828 MAX829 RLOAD = 10k MAX828 MAX829 IOUT = 5mA 1.5 6 19 CONDITIONS MIN TYP MAX 115 325 5.5 20 54.3 65 UNITS A V kHz
Note 2: All -40C to +85C specifications above are guaranteed by design.
2
_______________________________________________________________________________________
Switched-Capacitor Voltage Inverters
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1, VIN = +5V, C1 = C2 = C3, TA = +25C, 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
VIN = 4.75V, VOUT = -4.0V 40 OUTPUT CURRENT (mA) 35 30 25 20 15 10 5 0 VIN = 1.9V, VOUT = -1.5V VIN = 3.15V, VOUT = -2.5V
MAX828/829-03
40 35 OUTPUT RESISTANCE () 30 25 20 15 10 5 0 1.5 2.5 3.5 4.5 MAX828 MAX829
50 45 OUTPUT RESISTANCE () 40 35 30 25 20 15 10 VIN = 5.0V VIN = 3.3V VIN = 1.5V
45
5.5
-40
-20
0
20
40
60
80
0
5
10 15 20 25 30 35 40 45 50 CAPACITANCE (F)
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 VIN = 4.75V, VOUT = -4.0V VIN = 3.15V, VOUT = -2.5V VIN = 1.9V, VOUT = -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)
VIN = 4.75V, V- = -4.0V
500 450 400 350 300 250 200 150 100 50 0 0 5 10 15 20 25 VIN = 4.75V, VOUT = -4.0V VIN = 3.15V, VOUT = -2.5V VIN = 1.9V, VOUT = -1.5V
450
VIN = 3.15V, V- = -2.5V
VIN = 1.9V, V- = -1.5V
10
15
20
25
30
30
CAPACITANCE (F)
CAPACITANCE (F)
CAPACITANCE (F)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX828/829-07
MAX828 PUMP FREQUENCY vs. TEMPERATURE
MAX828/829-08
MAX829 PUMP FREQUENCY vs. TEMPERATURE
MAX828/829-9
200 175 SUPPLY CURRENT (A) 150 125 100 75 50 25 0 1.5 2.5 3.5 4.5 MAX828 MAX829
60 55 PUMP FREQUENCY (kHz) 50 45 40 35 30 25 20 15 10 VIN = 3.3V VIN = 5.0V VIN = 1.5V
55
PUMP FREQUENCY (kHz)
50
VIN = 1.5V
45
40 VIN = 3.3V VIN = 5.0V -40 -20 0 20 40 60 80 TEMPERATURE (C)
35
30 -40 -20 0 20 40 60 80 TEMPERATURE (C)
5.5
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
3
Switched-Capacitor Voltage Inverters MAX828/MAX829
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = +5V, C1 = C2 = C3, TA = +25C, unless otherwise noted.)
OUTPUT VOLTAGE vs. OUTPUT CURRENT
MAX828/829-10
EFFICIENCY vs. OUTPUT CURRENT
90 80 EFFICIENCY (%) 70 60 50 40 30 20 VIN = 2.0V VIN = 3.3V VIN = 5.0V
MAX828/829-11 MAX828/829-13
0.5 -0.5 OUTPUT VOLTAGE (V) VIN = 2.0V -1.5 VIN = 3.3V -2.5 -3.5 -4.5 -5.5 0 5
100
VIN = 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
VOUT 20mV/div
VOUT 20mV/div
20s/div VIN = 3.3V, VOUT = -3.2V, IOUT = 5mA, AC COUPLED
10s/div VIN = 3.3V, VOUT = -3.2V, IOUT = 5mA, AC COUPLED
_____________________Pin Description
PIN NAME OUT IN C1GND C1+ FUNCTION Inverting Charge-Pump Output Positive Power-Supply Input Flying Capacitor's Negative Terminal Ground Flying Capacitor's Positive Terminal
*10F (MAX828) 2 3 1 OUT IN MAX828 C3 3.3F* RL
VIN
1
2 3 4 5
VOUT C1+ 5 C2 3.3F* 4 C1 3.3F*
MAX829
C1GND
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 halfcycle, S1 and S3 open, S2 and S4 close, and C1 is level shifted downward by VIN volts. This connects C1 in parallel 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 VIN. The actual voltage at the output is more positive than -VIN, since switches S1-S4 have resistance and the load drains charge from C2.
S1 IN C1 S2
MAX828/MAX829
C2 S3 S4 VOUT = -(VIN)
Charge-Pump Output
The MAX828/MAX829 are not voltage regulators: the charge pump's output source resistance is approximately 20 at room temperature (with VIN = +5V), and VOUT approaches -5V when lightly loaded. VOUT will droop toward GND as load current increases. The droop of the negative supply (VDROOP-) equals the current draw from OUT (IOUT) times the negative converter's source resistance (RS-): VDROOP- = IOUT x RSThe negative output voltage will be: VOUT = -(VIN - VDROOP-)
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:
PUMP CAPACITOR LOSSES 2 =I xR OUT OUT
Efficiency Considerations
The power efficiency of a switched-capacitor voltage converter is affected by three factors: the internal losses 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: PLOSS = PINTERNAL LOSSES + PSWITCH LOSSES + PPUMP CAPACITOR LOSSES + PCONVERSION LOSSES
f
V+ VOUT
P
+P
CONVERSION LOSSES
R
OUT
(fOSC ) x C1
1
+ 4 2R
(
SWITCHES
+ ESR
C1
) + ESRC2
where fOSC is the oscillator frequency. The first term is the effective resistance from an ideal switchedcapacitor circuit. See Figures 3a and 3b.
REQUIV V+ 1 REQUIV = f x C1 C2 VOUT RL
C1
C2
RL
Figure 3a. Switched-Capacitor Model
Figure 3b. Equivalent Circuit
5
_______________________________________________________________________________________
Switched-Capacitor Voltage Inverters MAX828/MAX829
Conversion losses occur during the charge transfer between C1 and C2 when there is a voltage difference between them. The power loss is:
2 2 PCONV.LOSS = [1/ 2 C1 VIN - VOUT + 2 1/ 2 C2 VRIPPLE - 2VOUT VRIPPLE
] x fOSC
__________Applications Information
Capacitor Selection
To maintain the lowest output resistance, use capacitors with low ESR (Table 1). The charge-pump output resistance is a function of C1's and C2's ESR. Therefore, minimizing the charge-pump capacitor's ESR minimizes the total output resistance.
Input Bypass Capacitor Bypass the incoming supply to reduce its AC impedance and the impact of the MAX828/MAX829's switching noise. The recommended bypassing depends on the circuit configuration and on where the load is connected. When the inverter is loaded from OUT to GND, current from the supply switches between 2 x IOUT and zero. Therefore, use a large bypass capacitor (e.g., equal to the value of C1) if the supply has a high AC impedance.
When the inverter is loaded from IN to OUT, the circuit draws 2 x IOUT constantly, except for short switching spikes. A 0.1F bypass capacitor is sufficient.
Voltage Inverter
The most common application for these devices is a charge-pump voltage inverter (Figure 1). This application requires only two external components--capacitors C1 and C2--plus a bypass capacitor, if necessary. Refer to the Capacitor Selection section for suggested capacitor types and values.
Flying Capacitor (C1) Increasing the flying capacitor's size reduces the output resistance. Small C1 values increase the output resistance. Above a certain point, increasing C1's capacitance has a negligible effect, because the output resistance becomes dominated by the internal switch resistance and capacitor ESR. Output Capacitor (C2) Increasing the output capacitor's size reduces the output ripple voltage. Decreasing its ESR reduces both output resistance and ripple. Smaller capacitance values can be used with light loads if higher output ripple can be tolerated. Use the following equation to calculate the peak-to-peak ripple:
V
RIPPLE
Cascading Devices
Two devices can be cascaded to produce an even larger negative voltage (Figure 4). The unloaded output voltage is normally -2 x VIN, but this is reduced slightly by the output resistance of the first device multiplied by the quiescent current of the second. When cascading more than two devices, the output resistance rises dramatically. For applications requiring larger negative voltages, see the MAX864 and MAX865 data sheets.
Paralleling Devices
Paralleling multiple MAX828s or MAX829s reduces the output resistance. Each device requires its own pump capacitor (C1), but the reservoir capacitor (C2) serves all devices (Figure 5). Increase C2's value by a factor of n, where n is the number of parallel devices. The equation for calculating output resistance is also shown in Figure 5.
=
IOUT fOSC x C2
+ 2xI
OUT
x ESR
C2
Table 1. Low-ESR Capacitor Manufacturers
MANUFACTURER AVX Matsuo Sanyo Sprague 6 USA Japan PHONE (803) 946-0690 (800) 282-4975 (714) 969-2491 (619) 661-6835 81-7-2070-6306 (603) 224-1961 FAX (803) 626-3123 (714) 960-6492 (619) 661-1055 81-7-2070-1174 (603) 224-1430 DEVICE TYPE Surface-mount, TPS series Surface-mount, 267 series Through-hole, OS-CON series Surface-mount, 595D series
_______________________________________________________________________________________
Switched-Capacitor Voltage Inverters MAX828/MAX829
...
2 3 C1 4 5 +VIN 3 2 2
ROUT OF SINGLE DEVICE ROUT = NUMBER OF DEVICES
...
+VIN 2 3 3 1 VOUT C2 C1 4 5
MAX828 MAX829 "1"
C1 1
4 5
MAX828 MAX829 "n"
...
C2 VOUT = -nVIN
MAX870 MAX871 "1"
C1 1
4 5
MAX870 MAX871 "n"
1
VOUT
...
VOUT = -VIN C2
Figure 4. Cascading MAX828s or MAX829s to Increase Output Voltage
Figure 5. Paralleling MAX828s or MAX829s to Reduce Output Resistance
+VIN 3 C1 4 2 D1, D2 = 1N4148 GND 4
MAX828 MAX829
5 1
D1 VOUT = -VIN C2 D2 VOUT = (2VIN) (VFD1) - (VFD2) OUT 1
MAX870 MAX871
C3
C4
Figure 6. Combined Doubler and Inverter
Figure 7. High V- Load Current
Combined Doubler/Inverter
In the circuit of Figure 6, capacitors C1 and C2 form the inverter, while C3 and C4 form the doubler. C1 and C3 are the pump capacitors; C2 and C4 are the reservoir capacitors. Because both the inverter and doubler use part of the charge-pump circuit, loading either output causes both outputs to decline toward GND. Make sure the sum of the currents drawn from the two outputs does not exceed 40mA.
Heavy Output Current Loads
When under heavy loads, where higher supply is sourcing current into OUT, the OUT supply must not be pulled above ground. Applications that sink heavy current into OUT require a Schottky diode (1N5817) between GND and OUT, with the anode connected to OUT (Figure 7).
Layout and Grounding
Good layout is important, primarily for good noise performance. To ensure good layout, mount all components as close together as possible, keep traces short to minimize parasitic inductance and capacitance, and use a ground plane.
_______________________________________________________________________________________
7
Switched-Capacitor Voltage Inverters MAX828/MAX829
Shutting Down the MAX828/MAX829
If shutdown is necessary, use the circuit in Figure 8. The output resistance of the MAX828/MAX829 will typically be 20 plus two times the output resistance of the buffer driving IN. The 0.1F capacitor at the IN pin absorbs the transient input currents of the MAX828/MAX829. The output resistance of the buffer driving the IN pin can be reduced by connecting multiple buffers in parallel. The polarity of the SHUTDOWN signal can also be changed by using a noninverting buffer to drive IN.
INPUT 3 C1 5 4 C1IN 2 CIN 0.1F SHUTDOWN LOGIC SIGNAL OFF ON OUT 1 C2 OUTPUT
MAX828 C1+ MAX829
GND
Figure 8. Shutdown Control
___________________Chip Topography
C1+ IN
OUT
0.057" (1.45mm)
GND 0.038" (0.965mm)
C1-
TRANSISTOR COUNT: 58 SUBSTRATE CONNECTED TO IN
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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