电压转换模块MAX660

MAX660

Switched Capacitor Voltage Converter

General Description

The MAX660CMOS charge-pump voltage converter inverts a positive voltage in the range of 1.5V to 5.5V to the corre-sponding negative voltage.The MAX660uses two low cost capacitors to provide 100mA of output current without the cost,size,and EMI related to inductor based converters.With an operating current of only 120µA and operating effi-ciency greater than 90%at most loads,the MAX660pro-vides ideal performance for battery powered systems.The MAX660may also be used as a positive voltage doubler.The oscillator frequency can be lowered by adding an exter-nal capacitor to the OSC pin.Also,the OSC pin may be used to drive the MAX660with an external clock.A frequency con-trol (FC)pin selects the oscillator frequency of 10kHz or 80kHz.

Features

n Inverts or doubles input supply voltage n Narrow SO-8Package

n 6.5Ωtypical output resistance

n 88%typical conversion efficiency at 100mA n

Selectable oscillator frequency:10kHz/80kHz

Applications

n Laptop computers n Cellular phones n Medical instruments

n Operational amplifier power supplies n Interface power supplies n

Handheld instruments

Typical Application Circuits

Connection Diagram

Ordering Information

Order Number Top Mark Package Supplied as

MAX660M Date Code MAX660M M08A Rail (95units/rail)

MAX660MX

Date Code MAX660M

M08A

Tape and Reel (2500units/rail)

Voltage Inverter

DS1008-1

Positive Voltage Doubler

DS1008-2

8-Lead SO

DS1008-5

Top View

November 1999

MAX660Switched Capacitor Voltage Converter

©1999National Semiconductor Corporation DS1008www.national.com

Absolute Maximum Ratings (Note 1)

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 120mA Output Short-Circuit Duration to GND (Note 2)1sec.

Power Dissipation

(T A =25˚C)(Note 3)735mW T J Max (Note 3)150˚C θJA (Note 3)

170˚C/W

Operating Junction Temp.Range −40˚C to +85˚C Storage Temperature Range −65˚C to +150˚C

Lead Temperature

300˚C

(Soldering,10seconds)ESD Rating

2kV

Electrical Characteristics

Limits in standard typeface are for T J =25˚C,and limits in boldface type apply over the full operating temperature range.Un-less otherwise specified:V+=5V,FC =Open,C 1=C 2=150µF.(Note 4)Symbol Parameter

Condition

Min Typ

Max Units

V+

Supply Voltage

R L =1k

Inverter,LV =Open (Note 5)

3.5 5.5Inverter,LV =GND 1.5 5.5V Doubler,LV =OUT 2.5

5.5I Q Supply Current

No Load FC =Open 0.120.5mA LV =Open

FC =V+

13

I L Output Current

T A ≤+85˚C,OUT ≤−4V 100mA T A >+85˚C,OUT ≤−3.8V 100

R OUT Output Resistance (Note 6)I L =100mA T A ≤+85˚C 6.5

10ΩT A >+85˚C 12

F OSC Oscillator Frequency OSC =Open FC =Open 510kHz FC =V+

40

80

I OSC OSC Input Current FC =Open ±2µA

FC =V+

±16

P EFF

Power Efficiency

R L (1k)between V +and OUT 9698R L (500Ω)between GND and OUT 9296%I L =100mA to GND

88V OEFF Voltage Conversion Efficiency No Load

99

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 tem-peratures 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 P DMax =(T JMax −T A )/θJA ,where T JMax is the maximum junction temperature,T A is the ambient temperature,and θJA is the junction-to-ambient thermal resistance of the specified package.

Note 4:In the test circuit,capacitors C 1and C 2are 0.2Ωmaximum ESR capacitors.Capacitors with higher ESR will increase output resistance,reduce output volt-age 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 be-low 3.5V,connect the LV pin to GND.

Note 6:Specified output resistance includes internal switch resistance and capacitor ESR.

M A X 660

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Typical Performance Characteristics(Circuit of Figure1)DS1008-4

FIGURE1.MAX660Test Circuit

Supply Current vs

Supply Voltage

DS1008-36Supply Current vs

Oscillator Frequency

DS1008-37

Output Source Resistance

vs Supply Voltage

DS1008-38

Output Source Resistance

vs Temperature

DS1008-39Efficiency vs Load

Load Current

DS1008-40

Output Voltage Drop

vs Load Current

DS1008-41

MAX660

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Typical Performance Characteristics

(Circuit of Figure 1)(Continued)

Efficiency vs

Oscillator Frequency

DS1008-13Output Voltage vs Oscillator Frequency

DS1008-14Oscillator Frequency vs External Capacitance

DS1008-15

Oscillator Frequency Supply Voltage (FC =V+)

DS1008-16

Oscillator Frequency vs Supply Voltage (FC =Open)

DS1008-17

Oscillator Frequency vs Temperature (FC =V+)

DS1008-18

Oscillator Frequency vs Temperature (FC =Open)

DS1008-19

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Pin Description

Pin Name

Function

Voltage Inverter

Voltage Doubler

1

FC

Frequency control for internal oscillator:Same as inverter.

FC =open,f OSC =10kHz (typ);FC =V+,f OSC =80kHz (typ);

FC has no effect when OSC pin is driven externally.

2CAP+Connect this pin to the positive terminal of charge-pump capacitor.Same as inverter.

3GND Power supply ground input.

Power supply positive voltage input.4CAP−Connect this pin to the negative terminal of charge-pump capacitor.Same as inverter.

5OUT 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.

7OSC

Oscillator control input.OSC is connected to an internal 15pF 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.

8V+Power supply positive voltage input.

Positive voltage output.

Circuit Description

The MAX660contains four large CMOS switches which are switched in a sequence to invert the input supply voltage.Energy transfer and storage are provided by external capaci-tors.Figure 2illustrates the voltage conversion scheme.When S 1and S 3are closed,C 1charges to the supply volt-age V+.During this time interval switches S 2and S 4are open.In the second time interval,S 1and S 3are open and S 2and S 4are closed,C 1is charging C 2.After a number of cycles,the voltage across C 2will be pumped to V+.Since the anode of C 2is connected to ground,the output at the cathode of C 2equals −(V+)assuming no load on C 2,no loss in the switches,and no ESR in the capacitors.In reality,the charge transfer efficiency depends on the switching fre-quency,the on-resistance of the switches,and the ESR of the capacitors.

Application Information

SIMPLE NEGATIVE VOLTAGE CONVERTER

The main application of MAX660is to generate a negative supply voltage.The voltage inverter circuit uses only two ex-ternal 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 sup-ply 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 MAX660for the LMC7660Switched Capacitor Voltage Converter.

The output characteristics of this circuit can be approximated by an ideal voltage source in series with a resistor.The volt-age source equals −(V+).The output resistance R out is a function of the ON resistance of the internal MOS switches,the oscillator frequency,and the capacitance and ESR of C 1and C 2.A good approximation is:

where R SW 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 resis-tance.Instead of increasing the capacitance,the oscillator frequency can be increased to reduce the 2/(f osc x C 1)term.Once this term is trivial compared with R SW and ESRs,fur-ther 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 C 2:

DS1008-21

FIGURE 2.Voltage Inverting Principle

MAX660

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Application Information

(Continued)

Again,using a low ESR capacitor will result in lower ripple.POSITIVE VOLTAGE DOUBLER

The MAX660can operate as a positive voltage doubler (as shown in the Typical Application Circuits).The doubling func-tion 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 D 1’s for-ward drop.

The Schottky diode D 1is only needed for start-up.The inter-nal oscillator circuit uses the V+pin and the LV pin (con-nected 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,D 1is 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 di-ode D 1should have enough current carrying capability to charge the output capacitor at start-up,as well as a low for-ward voltage to prevent the internal parasitic diode from turning-on.A Schottky diode like 1N5817can be used for most applications.If the input voltage ramp is less than 10V/ms,a smaller Schottky diode like MBR0520LT1can be used to reduce the circuit size.SPLIT V+IN HALF

Another interesting application shown in the Basic Applica-tion Circuits is using the MAX660as a precision voltage di-vider.Since the off-voltage across each switch equals V IN /2,the input voltage can be raised to +11V.

CHANGING OSCILLATOR FREQUENCY

The internal oscillator frequency can be selected using the Frequency Control (FC)pin.When FC is open,the oscillator frequency is 10kHz;when FC is connected to V+,the fre-quency increases to 80kHz.A higher oscillator frequency al-

lows smaller capacitors to be used for equivalent output re-sistance and ripple,but increases the typical supply current from 0.12mA to 1mA.

The oscillator frequency can be lowered by adding an exter-nal capacitor between OSC and GND.(See Typical Perfor-mance Characteristics.)Also,in the inverter mode,an exter-nal clock that swings within 100mV of V+and GND can be used to drive OSC.Any CMOS logic gate is suitable for driv-ing OSC.LV must be grounded when driving OSC.The maximum external clock frequency is limited to 150kHz.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.MAX660Oscillator Frequency Selection FC OSC Oscillator Open Open 10kHz V+Open 80kHz 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 sec-tion,the output resistance and ripple voltage are dependent on the capacitance and ESR values of the external capaci-tors.The output voltage drop is the load current times the output resistance,and the power efficiency is

Where I Q (V+)is the quiescent power loss of the IC device,and I L 2R OUT is the conversion loss associated with the switch on-resistance,the two external capacitors and their ESRs.

Since the switching current charging and discharging C 1is approximately twice as the output current,the effect of the ESR of the pumping capacitor C 1is multiplied by four in the output resistance.The output capacitor C 2is charging and discharging at a current approximately equal to the output current,therefore,its ESR only counts once in the output re-sistance.However,the ESR of C 2directly affects the output voltage ripple.Therefore,low ESR capacitors (Table 2)are recommended for both capacitors to maximize efficiency,re-duce the output voltage drop and voltage ripple.For conve-nience,C 1and C 2are usually chosen to be the same.The output resistance varies with the oscillator frequency and the capacitors.In Figure 4,the output resistance vs.os-cillator frequency curves are drawn for three different tanta-lum capacitors.At very low frequency range,capacitance plays the most important role in determining the output resis-tance.Once the frequency is increased to some point (such as 20kHz for the 150µF 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.

DS1008-3

FIGURE 3.Splitting V IN in Half

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Application Information

(Continued)

TABLE 2.Low ESR Capacitor Manufacturers

Manufacturer Phone FAX Capacitor Type

Nichicon Corp.(708)-843-7500(708)-843-2798PL,PF series,through-hole aluminum electrolytic AVX Corp.(803)-448-9411(803)-448-1943TPS series,surface-mount tantalum

Sprague (207)-324-4140(207)-324-7223593D,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 C 1,while only one output capacitor C out is needed as shown in Figure 5.The composite output resistance is:

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 V out is (−nV in ).The effective output resistance is equal to the weighted sum of each individual device:

DS1008-32

FIGURE 4.Output Source Resistance vs Oscillator Frequency

DS1008-7

FIGURE 5.Lowering Output Resistance by Paralleling Devices

MAX660

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Other Applications

(Continued)

A three-stage cascade circuit shown in Figure 7generates −3V in ,from V in .

Cascading is also possible when devices are operating in doubling mode.In Figure 8,two devices are cascaded to generate 3V in .An example of using the circuit in Figure 7or Figure 8is 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 out-put resistance and output voltage ripple.

REGULATING V out

It is possible to regulate the output of the MAX660by 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 V ref =1.235V.

DS1008-8

FIGURE 6.Increasing Output Voltage by Cascading Devices

DS1008-9

FIGURE 7.Generating −3V in from +V in

DS1008-10

FIGURE 8.Generating +3V in from +V in

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Other Applications

(Continued)

The error flag on pin 5of the LP2951goes low when the regulated output at pin 4drops by about 5%.The LP2951can be shut-down by taking pin 3high.

Also,as shown in Figure 10by operating MAX660in 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.

DS1008-11

FIGURE 9.Combining MAX660with LP2951to Make a Negative Adjustable Regulator

DS1008-12

FIGURE 10.Generating +5V from +3V Input Voltage

MAX660

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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 LM26

LM2665LM3350LM3351MAX660Package

SOT23-6SOT23-6Mini SO-8Mini SO-8

SO-8Supply Current (typ.,mA)0.220.22 3.75 1.10.12at 10kHz,1.0at 80kHz

Output Ω(typ.)1212 4.2 4.2 6.5Oscillator (kHz)808080020010,80Input (V) 1.8to 5.5 1.8to 5.5 2.5to 6.25 2.5to 6.25 1.8to 5.5Output Mode(s)

Invert Double 3/2,2/33/2,2/3Invert,Double

LM2660

LM2661LM2662LM2663Package

Mini SO-8,SO-8Mini SO-8,SO-8

SO-8SO-8Supply Current (typ.,mA)0.12at 10kHz,1.0at 80kHz

1.00.3at 10kHz,1.3at 70kHz

1.3Output Ω(typ.) 6.5 6.5 3.5 3.5Oscillator (kHz)10,808010,7070Input (V) 1.8to 5.5 1.8to 5.5 1.8to 5.5 1.8to 5.5Output Mode(s)

Invert,Double

Invert,Double

Invert,Double

Invert,Double

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Physical Dimensions

inches (millimeters)unless otherwise noted

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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.

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8-Lead SO (M)

Order Number MAX660M NS Package Number M08A

MAX660Switched Capacitor Voltage Converter

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.