MAX828EUK ,Switched-Capacitor Voltage InvertersApplicationsMAX828C/D 0°C to +70°C Dice* —Small LCD Panels MAX828EUK -40°C to +85°C 5 SOT23-5 AABIM ..
MAX828EUK ,Switched-Capacitor Voltage Invertersapplications.' Requires Only Two CapacitorsThe MAX828/MAX829 combine low quiescent currentand high ..
MAX828EUK+ ,Switched-Capacitor Voltage InvertersFeaturesThe ultra-small MAX828/MAX829 monolithic, CMOS♦ 5-Pin SOT23-5 Package charge-pump inverters ..
MAX828EUK+T ,Switched-Capacitor Voltage InvertersApplications include generating a -5V supply from a +5Vlogic supply to power analog circuitry. Both ..
MAX828EUK-T ,Switched-Capacitor Voltage InvertersApplicationsSmall LCD PanelsCell PhonesMedical InstrumentsHandy-Terminals, PDAsBattery-Operated Equ ..
MAX828EUK-T ,Switched-Capacitor Voltage InvertersApplicationsSmall LCD PanelsCell PhonesMedical InstrumentsHandy-Terminals, PDAsBattery-Operated Equ ..
MB81C81A-35 ,CMOS 256K-BIT HIGH-SPEED SRAMMay 1990 00
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MAX828EUK-MAX829EUK
Switched-Capacitor Voltage Inverters
_______________General DescriptionThe 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 applications requiring more power, the MAX860
delivers up to 50mA with a voltage drop of 600mV, in a
space-saving µMAX package.
________________________ApplicationsSmall LCD Panels
Cell Phones
Medical Instruments
Handy-Terminals, PDAs
Battery-Operated Equipment
____________________________Features5-Pin SOT23-5 Package 95% Voltage Conversion EfficiencyInverts Input Supply Voltage60µA Quiescent Current (MAX828)+1.5V to +5.5V Input Voltage Range Requires Only Two Capacitors25mA Output Current
MAX828/MAX829
Switched-Capacitor Voltage Inverters
__________________Pin Configuration
__________Typical Operating Circuit19-0495; Rev 2; 4/97
MAX828/MAX829
Switched-Capacitor Voltage Inverters
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VIN= +5V, C1 = C2 = 10µF (MAX828), C1 = C2 = 3.3µF (MAX829), TA= 0°C to +85°C, unless otherwise noted. Typical values
are at TA= +25°C.)
ELECTRICAL CHARACTERISTICS(VIN= +5V, C1 = C2 = 10µF (MAX828), C1 = C2 = 3.3µF (MAX829), TA= -40°C to +85°C, unless otherwise noted. Typical values
are at TA= +25°C.) (Note 2)
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.
Note 1:Capacitor contribution is approximately 20% of the output impedance [ESR + 1 / (pump frequency x capacitance)].
Note 2:All -40°C to +85°C specifications above are guaranteed by design.
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= +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, 10sec).............................+300°C
MAX828/MAX829
Switched-Capacitor Voltage Inverters
__________________________________________Typical Operating Characteristics(Circuit of Figure 1, VIN= +5V, C1 = C2 = C3, TA= +25°C, unless otherwise noted.)
_____________________Pin Description
MAX828/MAX829
Switched-Capacitor Voltage Inverters
____________________________Typical Operating Characteristics (continued)(Circuit of Figure 1, VIN= +5V, C1 = C2 = C3, TA= +25°C, unless otherwise noted.)
_______________Detailed DescriptionThe 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 VINvolts. 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 -
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.
Charge-Pump OutputThe MAX828/MAX829 are not voltage regulators: the
charge pump’s output source resistance is approxi-
mately 20Ωat room temperature (with VIN= +5V), and
VOUTapproaches -5V when lightly loaded. VOUTwill
droop toward GND as load current increases. The
droop of the negative supply (VDROOP-) equals the cur-
rent draw from OUT (IOUT) times the negative convert-
er’s source resistance (RS-):
VDROOP-= IOUTx RS-
The negative output voltage will be:
VOUT= -(VIN- VDROOP-)
Efficiency ConsiderationsThe 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:
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:
where fOSCis the oscillator frequency. The first term is
the effective resistance from an ideal switched-
capacitor circuit. See Figures 3a and 3b.
CONVERSIONLOSSES
MAX828/MAX829
Switched-Capacitor Voltage InvertersFigure 3b. Equivalent Circuit
MAX828/MAX829
Switched-Capacitor Voltage InvertersConversion losses occur during the charge transfer
between C1 and C2 when there is a voltage difference
between them. The power loss is:
__________Applications Information
Capacitor SelectionTo maintain the lowest output resistance, use capaci-
tors 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.
Flying Capacitor (C1)Increasing the flying capacitor’s size reduces the out-
put resistance. Small C1 values increase the output
resistance. Above a certain point, increasing C1’s
capacitance has a negligible effect, because the out-
put resistance becomes dominated by the internal
switch resistance and capacitor ESR.
Output Capacitor (C2)Increasing the output capacitor’s size reduces the out-
put ripple voltage. Decreasing its ESR reduces both
output resistance and ripple. Smaller capacitance val-
ues can be used with light loads if higher output ripple
can be tolerated. Use the following equation to calcu-
late the peak-to-peak ripple:
Input Bypass CapacitorBypass the incoming supply to reduce its AC impedance
and the impact of the MAX828/MAX829’s switching
noise. The recommended bypassing depends on the cir-
cuit 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 IOUTand 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 IOUTconstantly, except for short switching
spikes. A 0.1µF bypass capacitor is sufficient.
Voltage InverterThe most common application for these devices is a
charge-pump voltage inverter (Figure 1). This applica-
tion 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.
Cascading DevicesTwo 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 dra-
matically. For applications requiring larger negative
voltages, see the MAX864 and MAX865 data sheets.
Paralleling DevicesParalleling 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.
OSC
