TI MAX660 Switched capacitor voltage converter Datasheet

MAX660
MAX660 Switched Capacitor Voltage Converter
Literature Number: SNOS405
MAX660
Switched Capacitor Voltage Converter
General Description
Features
The MAX660 CMOS charge-pump voltage converter inverts
a positive voltage in the range of 1.5V to 5.5V to the corresponding negative voltage. The MAX660 uses two low cost
capacitors to provide 100 mA of output current without the
cost, size, and EMI related to inductor based converters.
With an operating current of only 120 µA and operating efficiency greater than 90% at most loads, the MAX660 provides ideal performance for battery powered systems. The
MAX660 may also be used as a positive voltage doubler.
The oscillator frequency can be lowered by adding an external capacitor to the OSC pin. Also, the OSC pin may be used
to drive the MAX660 with an external clock. A frequency control (FC) pin selects the oscillator frequency of 10 kHz or 80
kHz.
n
n
n
n
n
Inverts or doubles input supply voltage
Narrow SO-8 Package
6.5Ω typical output resistance
88% typical conversion efficiency at 100 mA
Selectable oscillator frequency: 10 kHz/80 kHz
Applications
n
n
n
n
n
n
Laptop computers
Cellular phones
Medical instruments
Operational amplifier power supplies
Interface power supplies
Handheld instruments
Typical Application Circuits
Positive Voltage Doubler
Voltage Inverter
DS100898-1
DS100898-2
Connection Diagram
8-Lead SO
DS100898-5
Top View
Ordering Information
Order Number
Top Mark
Package
MAX660M
Date Code
MAX660M
M08A
Rail (95 units/rail)
MAX660MX
Date Code
MAX660M
M08A
Tape and Reel (2500 units/rail)
© 1999 National Semiconductor Corporation
DS100898
Supplied as
www.national.com
MAX660 Switched Capacitor Voltage Converter
November 1999
MAX660
Absolute Maximum Ratings (Note 1)
Power Dissipation
(TA = 25˚C) (Note 3)
TJ Max (Note 3)
θJA (Note 3)
Operating Junction Temp. Range
Storage Temperature Range
Lead Temperature
(Soldering, 10 seconds)
ESD Rating
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (V+ to GND, or GND to OUT)
6V
LV
(OUT − 0.3V) to (GND + 3V)
FC, OSC
The least negative of (OUT − 0.3V)
or (V+ − 6V) to (V+ + 0.3V)
V+ and OUT Continuous Output Current
120 mA
Output Short-Circuit Duration to GND (Note 2)
1 sec.
735 mW
150˚C
170˚C/W
−40˚C to +85˚C
−65˚C to +150˚C
300˚C
2 kV
Electrical Characteristics
Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the full operating temperature range. Unless otherwise specified: V+ = 5V, FC = Open, C1 = C2 = 150 µF. (Note 4)
Symbol
V+
IQ
IL
ROUT
FOSC
IOSC
PEFF
VOEFF
Parameter
Supply Voltage
Supply Current
Condition
RL = 1k
Inverter, LV = Open
(Note 5)
Inverter, LV = GND
Doubler, LV = OUT
Min
1.5
5.5
2.5
5.5
Output Current
TA ≤ +85˚C, OUT ≤ −4V
100
100
Output Resistance (Note 6)
TA > +85˚C, OUT ≤ −3.8V
IL = 100 mA
TA ≤ +85˚C
Oscillator Frequency
OSC Input Current
Power Efficiency
Voltage Conversion Efficiency
OSC = Open
0.12
0.5
1
3
6.5
5
10
FC = V+
40
80
10
12
±2
± 16
FC = Open
FC = V+
Units
V
mA
mA
TA > +85˚C
FC = Open
+
Max
5.5
FC = Open
FC = V+
No Load
LV = Open
Typ
3.5
RL (1k) between V and OUT
96
98
RL (500Ω) between GND and OUT
IL = 100 mA to GND
92
96
No Load
99
Ω
kHz
µA
%
88
99.96
%
Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device
beyond its rated operating conditions.
Note 2: OUT may be shorted to GND for one second without damage. However, shorting OUT to V+ may damage the device and should be avoided. Also, for temperatures above 85˚C, OUT must not be shorted to GND or V+, or device may be damaged.
Note 3: The maximum allowable power dissipation is calculated by using PDMax = (TJMax − TA)/θJA, where TJMax is the maximum junction temperature, TA is the
ambient temperature, and θJA is the junction-to-ambient thermal resistance of the specified package.
Note 4: In the test circuit, capacitors C1 and C2 are 0.2Ω maximum ESR capacitors. Capacitors with higher ESR will increase output resistance, reduce output voltage and efficiency.
Note 5: The minimum limit for this parameter is different from the limit of 3.0V for the industry-standard “660” product. For inverter operation with supply voltage below 3.5V, connect the LV pin to GND.
Note 6: Specified output resistance includes internal switch resistance and capacitor ESR.
www.national.com
2
MAX660
Test Circuit
DS100898-4
FIGURE 1. MAX660 Test Circuit
Typical Performance Characteristics
Supply Current vs
Supply Voltage
(Circuit of Figure 1)
Supply Current vs
Oscillator Frequency
DS100898-36
Output Source Resistance
vs Temperature
Output Source Resistance
vs Supply Voltage
DS100898-38
DS100898-37
Efficiency vs Load
Load Current
DS100898-39
Output Voltage Drop
vs Load Current
DS100898-40
3
DS100898-41
www.national.com
MAX660
Typical Performance Characteristics
Efficiency vs
Oscillator Frequency
(Circuit of Figure 1) (Continued)
Output Voltage vs
Oscillator Frequency
DS100898-13
Oscillator Frequency
Supply Voltage
(FC = V+)
DS100898-14
Oscillator Frequency vs
Supply Voltage
(FC = Open)
DS100898-16
DS100898-19
4
DS100898-15
Oscillator Frequency vs
Temperature
(FC = V+)
DS100898-17
Oscillator Frequency
vs Temperature
(FC = Open)
www.national.com
Oscillator Frequency
vs External Capacitance
DS100898-18
MAX660
Pin Description
Pin
Name
Function
Voltage Inverter
1
FC
Voltage Doubler
Frequency control for internal oscillator:
FC = open, fOSC = 10 kHz (typ);
Same as inverter.
FC = V+, fOSC = 80 kHz (typ);
FC has no effect when OSC pin is driven externally.
2
CAP+
Connect this pin to the positive terminal of
charge-pump capacitor.
Same as inverter.
3
GND
Power supply ground input.
Power supply positive voltage input.
4
CAP−
Connect this pin to the negative terminal of
charge-pump capacitor.
Same as inverter.
5
OUT
Negative voltage output.
Power supply ground input.
6
LV
Low-voltage operation input. Tie LV to GND when
input voltage is less than 3.5V. Above 3.5V, LV can
be connected to GND or left open. When driving
OSC with an external clock, LV must be connected
to GND.
LV must be tied to OUT.
7
OSC
Oscillator control input. OSC is connected to an
internal 15 pF capacitor. An external capacitor can
be connected to slow the oscillator. Also, an
external clock can be used to drive OSC.
Same as inverter except that OSC cannot be driven
by an external clock.
8
V+
Power supply positive voltage input.
Positive voltage output.
Circuit Description
Application Information
The MAX660 contains four large CMOS switches which are
switched in a sequence to invert the input supply voltage.
Energy transfer and storage are provided by external capacitors. Figure 2 illustrates the voltage conversion scheme.
When S1 and S3 are closed, C1 charges to the supply voltage V+. During this time interval switches S2 and S4 are
open. In the second time interval, S1 and S3 are open and S2
and S4 are closed, C1 is charging C2. After a number of
cycles, the voltage across C2 will be pumped to V+. Since
the anode of C2 is connected to ground, the output at the
cathode of C2 equals −(V+) assuming no load on C2, no loss
in the switches, and no ESR in the capacitors. In reality, the
charge transfer efficiency depends on the switching frequency, the on-resistance of the switches, and the ESR of
the capacitors.
SIMPLE NEGATIVE VOLTAGE CONVERTER
The main application of MAX660 is to generate a negative
supply voltage. The voltage inverter circuit uses only two external capacitors as shown in the Typical Application Circuits.
The range of the input supply voltage is 1.5V to 5.5V. For a
supply voltage less than 3.5V, the LV pin must be connected
to ground to bypass the internal regulator circuitry. This gives
the best performance in low voltage applications. If the supply voltage is greater than 3.5V, LV may be connected to
ground or left open. The choice of leaving LV open simplifies
the direct substitution of the MAX660 for the LMC7660
Switched Capacitor Voltage Converter.
The output characteristics of this circuit can be approximated
by an ideal voltage source in series with a resistor. The voltage source equals −(V+). The output resistance Rout is a
function of the ON resistance of the internal MOS switches,
the oscillator frequency, and the capacitance and ESR of C1
and C2. A good approximation is:
where RSW is the sum of the ON resistance of the internal
MOS switches shown in Figure 2.
High value, low ESR capacitors will reduce the output resistance. Instead of increasing the capacitance, the oscillator
frequency can be increased to reduce the 2/(fosc x C1) term.
Once this term is trivial compared with RSW and ESRs, further increasing in oscillator frequency and capacitance will
become ineffective.
The peak-to-peak output voltage ripple is determined by the
oscillator frequency, and the capacitance and ESR of the
output capacitor C2:
DS100898-21
FIGURE 2. Voltage Inverting Principle
5
www.national.com
MAX660
Application Information
lows smaller capacitors to be used for equivalent output resistance and ripple, but increases the typical supply current
from 0.12 mA to 1 mA.
(Continued)
The oscillator frequency can be lowered by adding an external capacitor between OSC and GND. (See Typical Performance Characteristics.) Also, in the inverter mode, an external clock that swings within 100 mV of V+ and GND can be
used to drive OSC. Any CMOS logic gate is suitable for driving OSC. LV must be grounded when driving OSC. The
maximum external clock frequency is limited to 150 kHz.
Again, using a low ESR capacitor will result in lower ripple.
POSITIVE VOLTAGE DOUBLER
The MAX660 can operate as a positive voltage doubler (as
shown in the Typical Application Circuits). The doubling function is achieved by reversing some of the connections to the
device. The input voltage is applied to the GND pin with an
allowable voltage from 2.5V to 5.5V. The V+ pin is used as
the output. The LV pin and OUT pin must be connected to
ground. The OSC pin can not be driven by an external clock
in this operation mode. The unloaded output voltage is twice
of the input voltage and is not reduced by the diode D1’s forward drop.
The switching frequency of the converter (also called the
charge pump frequency) is half of the oscillator frequency.
Note: OSC cannot be driven by an external clock in the
voltage-doubling mode.
TABLE 1. MAX660 Oscillator Frequency Selection
The Schottky diode D1 is only needed for start-up. The internal oscillator circuit uses the V+ pin and the LV pin (connected to ground in the voltage doubler circuit) as its power
rails. Voltage across V+ and LV must be larger than 1.5V to
insure the operation of the oscillator. During start-up, D1 is
used to charge up the voltage at V+ pin to start the oscillator;
also, it protects the device from turning-on its own parasitic
diode and potentially latching-up. Therefore, the Schottky diode D1 should have enough current carrying capability to
charge the output capacitor at start-up, as well as a low forward voltage to prevent the internal parasitic diode from
turning-on. A Schottky diode like 1N5817 can be used for
most applications. If the input voltage ramp is less than
10V/ms, a smaller Schottky diode like MBR0520LT1 can be
used to reduce the circuit size.
OSC
Open
Open
Oscillator
10 kHz
V+
Open
80 kHz
Open
or V+
External
Capacitor
See Typical
Performance
Characteristics
N/A
External Clock
(inverter mode only)
External Clock
Frequency
CAPACITOR SELECTION
As discussed in the Simple Negative Voltage Converter section, the output resistance and ripple voltage are dependent
on the capacitance and ESR values of the external capacitors. The output voltage drop is the load current times the
output resistance, and the power efficiency is
SPLIT V+ IN HALF
Another interesting application shown in the Basic Application Circuits is using the MAX660 as a precision voltage divider. Since the off-voltage across each switch equals VIN/2,
the input voltage can be raised to +11V.
Where IQ(V+) is the quiescent power loss of the IC device,
and IL2ROUT is the conversion loss associated with the
switch on-resistance, the two external capacitors and their
ESRs.
Since the switching current charging and discharging C1 is
approximately twice as the output current, the effect of the
ESR of the pumping capacitor C1 is multiplied by four in the
output resistance. The output capacitor C2 is charging and
discharging at a current approximately equal to the output
current, therefore, its ESR only counts once in the output resistance. However, the ESR of C2 directly affects the output
voltage ripple. Therefore, low ESR capacitors (Table 2) are
recommended for both capacitors to maximize efficiency, reduce the output voltage drop and voltage ripple. For convenience, C1 and C2 are usually chosen to be the same.
The output resistance varies with the oscillator frequency
and the capacitors. In Figure 4, the output resistance vs. oscillator frequency curves are drawn for three different tantalum capacitors. At very low frequency range, capacitance
plays the most important role in determining the output resistance. Once the frequency is increased to some point (such
as 20 kHz for the 150 µF capacitors), the output resistance is
dominated by the ON resistance of the internal switches and
the ESRs of the external capacitors. A low value, smaller
size capacitor usually has a higher ESR compared with a
bigger size capacitor of the same type. For lower ESR, use
ceramic capacitors.
DS100898-3
FIGURE 3. Splitting VIN in Half
CHANGING OSCILLATOR FREQUENCY
The internal oscillator frequency can be selected using the
Frequency Control (FC) pin. When FC is open, the oscillator
frequency is 10 kHz; when FC is connected to V+, the frequency increases to 80 kHz. A higher oscillator frequency al-
www.national.com
FC
6
MAX660
Application Information
(Continued)
DS100898-32
FIGURE 4. Output Source Resistance vs Oscillator Frequency
TABLE 2. Low ESR Capacitor Manufacturers
Manufacturer
Phone
FAX
Nichicon Corp.
(708)-843-7500
(708)-843-2798
PL, PF series, through-hole aluminum electrolytic
Capacitor Type
AVX Corp.
(803)-448-9411
(803)-448-1943
TPS series, surface-mount tantalum
Sprague
(207)-324-4140
(207)-324-7223
593D, 594D, 595D series, surface-mount tantalum
Sanyo
(619)-661-6835
(619)-661-1055
OS-CON series, through-hole aluminum electrolytic
Other Applications
PARALLELING DEVICES
Any number of MAX660s can be paralleled to reduce the output resistance. Each device must have its own pumping capacitor
C1, while only one output capacitor Cout is needed as shown in Figure 5. The composite output resistance is:
DS100898-7
FIGURE 5. Lowering Output Resistance by Paralleling Devices
CASCADING DEVICES
Cascading the is an easy way to produce a greater negative voltage (as shown in Figure 6). If n is the integer representing the
number of devices cascaded, the unloaded output voltage Vout is (−nVin). The effective output resistance is equal to the weighted
sum of each individual device:
7
www.national.com
MAX660
Other Applications
(Continued)
A three-stage cascade circuit shown in Figure 7 generates −3Vin, from Vin.
Cascading is also possible when devices are operating in doubling mode. In Figure 8, two devices are cascaded to generate 3Vin.
An example of using the circuit in Figure 7 or Figure 8 is generating +15V or −15V from a +5V input.
Note that the number of n is practically limited since the increasing of n significantly reduces the efficiency and increases the output resistance and output voltage ripple.
DS100898-8
FIGURE 6. Increasing Output Voltage by Cascading Devices
DS100898-9
FIGURE 7. Generating −3Vin from +Vin
DS100898-10
FIGURE 8. Generating +3Vin from +Vin
REGULATING Vout
It is possible to regulate the output of the MAX660 by use of a low dropout regulator (such as LP2951). The whole converter is
depicted in Figure 9. This converter can give a regulated output from −1.5V to −5.5V by choosing the proper resistor ratio:
where Vref = 1.235V.
www.national.com
8
(Continued)
DS100898-11
FIGURE 9. Combining MAX660 with LP2951 to Make a Negative Adjustable Regulator
Also, as shown in Figure 10 by operating MAX660 in voltage doubling mode and adding a linear regulator (such as LP2981) at
the output, we can get +5V output from an input as low as +3V.
DS100898-12
FIGURE 10. Generating +5V from +3V Input Voltage
9
www.national.com
MAX660
Other Applications
The error flag on pin 5 of the LP2951 goes low when the regulated output at pin 4 drops by about 5%. The LP2951 can be shutdown by taking pin 3 high.
MAX660
Other Applications
(Continued)
OTHER SWITCHED-CAPACITOR CONVERTERS
Please refer to Table 3, which shows National’s Switched-Capacitor Converter products.
TABLE 3. Switched-Capacitor Converters
LM2664
LM2665
LM3350
LM3351
SOT23-6
SOT23-6
Mini SO-8
Mini SO-8
SO-8
0.22
0.22
3.75
1.1
0.12 at 10kHz,
1.0 at 80kHz
Output Ω (typ.)
12
12
4.2
4.2
6.5
Oscillator (kHz)
80
80
800
200
10, 80
1.8 to 5.5
1.8 to 5.5
2.5 to 6.25
2.5 to 6.25
1.8 to 5.5
Invert
Double
3/2, 2/3
3/2, 2/3
Invert, Double
Package
Supply Current (typ., mA)
Input (V)
Output Mode(s)
LM2660
LM2661
LM2662
LM2663
Mini SO-8, SO-8
Mini SO-8, SO-8
SO-8
SO-8
0.12 at 10kHz,
1.0 at 80kHz
1.0
0.3 at 10kHz,
1.3 at 70kHz
1.3
Output Ω (typ.)
6.5
6.5
3.5
3.5
Oscillator (kHz)
10, 80
80
10, 70
70
1.8 to 5.5
1.8 to 5.5
1.8 to 5.5
1.8 to 5.5
Invert, Double
Invert, Double
Invert, Double
Invert, Double
Package
Supply Current (typ., mA)
Input (V)
Output Mode(s)
www.national.com
10
MAX660
MAX660 Switched Capacitor Voltage Converter
Physical Dimensions
inches (millimeters) unless otherwise noted
8-Lead SO (M)
Order Number MAX660M
NS Package Number M08A
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: [email protected]
www.national.com
National Semiconductor
Europe
Fax: +49 (0) 1 80-530 85 86
Email: [email protected]
Deutsch Tel: +49 (0) 1 80-530 85 85
English Tel: +49 (0) 1 80-532 78 32
Français Tel: +49 (0) 1 80-532 93 58
Italiano Tel: +49 (0) 1 80-534 16 80
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: [email protected]
National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements,
and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should
obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are
sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment.
TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI’s standard
warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where
mandated by government requirements, testing of all parameters of each product is not necessarily performed.
TI assumes no liability for applications assistance or customer product design. Customers are responsible for their products and
applications using TI components. To minimize the risks associated with customer products and applications, customers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any TI patent right, copyright, mask work right,
or other TI intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information
published by TI regarding third-party products or services does not constitute a license from TI to use such products or services or a
warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual
property of the third party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of TI information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied
by all associated warranties, conditions, limitations, and notices. Reproduction of this information with alteration is an unfair and deceptive
business practice. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional
restrictions.
Resale of TI products or services with statements different from or beyond the parameters stated by TI for that product or service voids all
express and any implied warranties for the associated TI product or service and is an unfair and deceptive business practice. TI is not
responsible or liable for any such statements.
TI products are not authorized for use in safety-critical applications (such as life support) where a failure of the TI product would reasonably
be expected to cause severe personal injury or death, unless officers of the parties have executed an agreement specifically governing
such use. Buyers represent that they have all necessary expertise in the safety and regulatory ramifications of their applications, and
acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products
and any use of TI products in such safety-critical applications, notwithstanding any applications-related information or support that may be
provided by TI. Further, Buyers must fully indemnify TI and its representatives against any damages arising out of the use of TI products in
such safety-critical applications.
TI products are neither designed nor intended for use in military/aerospace applications or environments unless the TI products are
specifically designated by TI as military-grade or "enhanced plastic." Only products designated by TI as military-grade meet military
specifications. Buyers acknowledge and agree that any such use of TI products which TI has not designated as military-grade is solely at
the Buyer's risk, and that they are solely responsible for compliance with all legal and regulatory requirements in connection with such use.
TI products are neither designed nor intended for use in automotive applications or environments unless the specific TI products are
designated by TI as compliant with ISO/TS 16949 requirements. Buyers acknowledge and agree that, if they use any non-designated
products in automotive applications, TI will not be responsible for any failure to meet such requirements.
Following are URLs where you can obtain information on other Texas Instruments products and application solutions:
Products
Applications
Audio
www.ti.com/audio
Communications and Telecom www.ti.com/communications
Amplifiers
amplifier.ti.com
Computers and Peripherals
www.ti.com/computers
Data Converters
dataconverter.ti.com
Consumer Electronics
www.ti.com/consumer-apps
DLP® Products
www.dlp.com
Energy and Lighting
www.ti.com/energy
DSP
dsp.ti.com
Industrial
www.ti.com/industrial
Clocks and Timers
www.ti.com/clocks
Medical
www.ti.com/medical
Interface
interface.ti.com
Security
www.ti.com/security
Logic
logic.ti.com
Space, Avionics and Defense
www.ti.com/space-avionics-defense
Power Mgmt
power.ti.com
Transportation and Automotive www.ti.com/automotive
Microcontrollers
microcontroller.ti.com
Video and Imaging
RFID
www.ti-rfid.com
OMAP Mobile Processors
www.ti.com/omap
Wireless Connectivity
www.ti.com/wirelessconnectivity
TI E2E Community Home Page
www.ti.com/video
e2e.ti.com
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2011, Texas Instruments Incorporated