Switched-Capacitor Voltage Converters

The Maxim ICL7660 can also be used with an external output diode in series with pin 5 ... This connects C1 in parallel with ... Switched-Capacitor Vol...

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19-4667; Rev 1; 7/94

Switched-Capacitor Voltage Converters

________________________Applications -5V Supply from +5V Logic Supply Personal Communications Equipment Portable Telephones Op-Amp Power Supplies EIA/TIA-232E and EIA/TIA-562 Power Supplies Data-Acquisition Systems Hand-Held Instruments Panel Meters

__________Typical Operating Circuit

____________________________Features ♦ Miniature µMAX Package ♦ 1.5V to 10.0V Operating Supply Voltage Range ♦ 98% Typical Power-Conversion Efficiency ♦ Invert, Double, Divide, or Multiply Input Voltages ♦ BOOST Pin Increases Switching Frequencies (MAX1044) ♦ No-Load Supply Current: 200µA Max at 5V ♦ No External Diode Required for Higher-Voltage Operation

______________Ordering Information PART

TEMP. RANGE

MAX1044CPA

0°C to +70°C

PIN-PACKAGE 8 Plastic DIP

MAX1044CSA MAX1044C/D MAX1044EPA

0°C to +70°C 0°C to +70°C -40°C to +85°C

8 SO Dice* 8 Plastic DIP

Ordering Information continued at end of data sheet. * Contact factory for dice specifications.

_________________Pin Configurations TOP VIEW (N.C.) BOOST

1

CAP+

2

GND

3

CAP-

4

MAX1044 ICL7660

8

V+

7

OSC

6

LV

5

VOUT

DIP/SO/µMAX V+

CAP+

INPUT SUPPLY VOLTAGE

V+ AND CASE 8

N.C. 1

OSC 7

MAX1044 ICL7660 CAP+ CAPVOUT

NEGATIVE OUTPUT VOLTAGE

2

GND

GND

6

ICL7660

5

3

LV

VOUT

4

NEGATIVE VOLTAGE CONVERTER

CAP( ) ARE FOR ICL7660

TO-99

________________________________________________________________ Maxim Integrated Products

Call toll free 1-800-998-8800 for free samples or literature.

1

MAX1044/ICL7660

_______________General Description The MAX1044 and ICL7660 are monolithic, CMOS switched-capacitor voltage converters that invert, double, divide, or multiply a positive input voltage. They are pin compatible with the industry-standard ICL7660 and LTC1044. Operation is guaranteed from 1.5V to 10V with no external diode over the full temperature range. They deliver 10mA with a 0.5V output drop. The MAX1044 has a BOOST pin that raises the oscillator frequency above the audio band and reduces external capacitor size requirements. The MAX1044/ICL7660 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. For applications requiring more power, the MAX660 delivers up to 100mA with a voltage drop of less than 0.65V.

MAX1044/ICL7660

Switched-Capacitor Voltage Converters ABSOLUTE MAXIMUM RATINGS Supply Voltage (V+ to GND, or GND to VOUT)....................10.5V Input Voltage on Pins 1, 6, and 7 .........-0.3V ≤ VIN ≤ (V+ + 0.3V) LV Input Current ..................................................................20µA Output Short-Circuit Duration (V+ ≤ 5.5V)..................Continuous Continuous Power Dissipation (TA = +70°C) Plastic DIP (derate 9.09mW/°C above +70°C) ............727mW SO (derate 5.88mW/°C above +70°C) .........................471mW µMAX (derate 4.1mW/°C above +70°C) ......................330mW

CERDIP (derate 8.00mW/°C above +70°C) .................640mW TO-99 (derate 6.67mW/°C above +70°C) ....................533mW Operating Temperature Ranges MAX1044C_ _ /ICL7660C_ _ ..............................0°C to +70°C MAX1044E_ _ /ICL7660E_ _ ............................-40°C to +85°C MAX1044M_ _ /ICL7660M_ _ ........................-55°C to +125°C Storage Temperature Range ............................-65°C to + 150°C Lead Temperature (soldering, 10sec) .............................+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 (Circuit of Figure 1, V+ = 5.0V, LV pin = 0V, BOOST pin = open, ILOAD = 0mA, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER

Supply Current

CONDITIONS RL = ∞, pins 1 and 7 no connection, LV open

MAX1044 MIN TYP MAX

ICL7660 MIN TYP MAX

30

80

TA = +25°C

175

TA = 0°C to +70°C

200

225

TA = -40°C to +85°C

200

250

TA = -55°C to +125°C

200

250

RL = ∞, pins 1 and 7 = V+ = 3V Supply Voltage Range (Note 1)

200

1.5 TA = +25°C

10 65

IL = 20mA, fOSC = 5kHz, LV open

TA = 0°C to +70°C TA = -40°C to +85°C TA = -55°C to +125°C Output Resistance fOSC = 2.7kHz (ICL7660), TA = +25°C fOSC = 1kHz (MAX1044), TA = 0°C to +70°C V+ = 2V, IL = 3mA, TA = -40°C to +85°C LV to GND TA = -55°C to +125°C V+ = 5V COSC = 1pF, Oscillator Frequency LV to GND (Note 2) V+ = 2V Power Efficiency RL = 5kΩ, TA = +25°C, fOSC 5kHz, LV open Voltage Conversion Efficiency RL = ∞, TA = +25°C, LV open Pin 1 = 0V Oscillator Sink or VOSC = 0V or V+, LV open Source Current Pin 1 = V+ V+ = 2V Oscillator Impedance TA = +25°C V+ = 5V

µA

10

RL = 10kΩ, LV open RL = 10kΩ, LV to GND

UNITS

3.0

10.0

1.5

3.5

100

55

130 130 150 325 325 325 400 5 1 95 98 97.0 99.9

100 120 140 150 250 300 300 400

10 95 98 99.0 99.9 3 20

1.0 100

V



kHz % % µA

1.0 100

MΩ kΩ

Note 1: The Maxim ICL7660 and MAX1044 can operate without an external output diode over the full temperature and voltage ranges. The Maxim ICL7660 can also be used with an external output diode in series with pin 5 (cathode at VOUT) when replacing the Intersil ICL7660. Tests are performed without diode in circuit. Note 2: fOSC is tested with COSC = 100pF to minimize the effects of test fixture capacitance loading. The 1pF frequency is correlated to this 100pF test point, and is intended to simulate pin 7’s capacitance when the device is plugged into a test socket with no external capacitor. For this test, the LV pin is connected to GND for comparison to the original manufacturer’s device, which automatically connects this pin to GND for (V+ > 3V).

2

_______________________________________________________________________________________

Switched-Capacitor Voltage Converters

150 C

V+ = 2V LV = GND

-0.5

100 50

OUTPUT RIPPLE

0 0

1

2

3

4

5

6

7

8

9

480 400

C

320

-2.0

C

-1.5

V+ = 5V LV = OPEN

B

240

-0.5 A

0

OUTPUT RIPPLE

0

10

0

5

10

15

20

25

30

35

C

-6 -5

490 420 350 280

-4 OUTPUT RIPPLE

-3

160

-2

80

-1

0

0

C

V+ = 10V LV = OPEN

70 0 0

40

5

10

15

20

25

30

35

50

5

40

SUPPLY CURRENT

4

60 50

3

20

2

20

1 0

V+ = 2V LV = GND

0 1

2

3

4

5

6

7

8

V+ = 5V LV = OPEN

0

0

0

5

10

15

20

25

30

35

MAX1044-Fig 7

EXTERNAL HCMOS OSCILLATOR

50 40

MAX1044 with BOOST -V+

102

103

104

105

OSCILLATOR FREQUENCY (Hz)

6x105

ICL7660 and MAX1044 with BOOST = OPEN

10 1

10

100

1000

COSC (pF)

MAX1044-Fig 6

15 10 V+ = 10V LV = OPEN

5 0

5

10

15

20

25

30

35

40

100,000

10,000

FROM TOP TO BOTTOM AT 5V MAX1044, BOOST = V+, LV = GND MAX1044, BOOST = V+, LV = OPEN ICL7660, LV = GND ICL7660, LV = OPEN MAX1044, BOOST = OPEN, LV = GND MAX1044, BOOST = OPEN, LV = OPEN

1000

100 1

20

OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE

0.1 101

25 SUPPLY CURRENT

0

1000 100

30

LOAD CURRENT (mA)

100,000 10,000

40

45

35

30

10

OSCILLATOR FREQUENCY vs. EXTERNAL CAPACITANCE

60

40

5

50

40

A: MAX1044 with BOOST = V+ B: ICL7660 C: MAX1044 with BOOST = OPEN

50

10 0

A EFFICIENCY

60

20

EFFICIENCY vs. OSCILLATOR FREQUENCY

C1, C2 = 1µF

70

20 15

LOAD CURRENT (mA)

C1, C2 = 10µF

80

SUPPLY CURRENT

LOAD CURRENT (mA)

C1, C2 = 100µF

90

25

B, C

70

10

9 10

100

80

35

30

OSCILLATOR FREQUENCY (Hz)

0

40

30

40

30

10

C

90

40

MAX1044-Fig 9

6

70

100

45

EFFICIENCY (%)

60

B A: MAX1044 with BOOST = V+ B: ICL7660 C: MAX1044 with BOOST = OPEN

50

SUPPLY CURRENT (mA)

7

A

EFFICIENCY

OSCILLATOR FREQUENCY (Hz)

70

MAX1044-Fig 5

80 EFFICIENCY (%)

8

SUPPLY CURRENT (mA)

MAX1044-Fig 4

EFFICIENCY

90

140

A

EFFICIENCY and SUPPLY CURRENT vs. LOAD CURRENT

100

210

B

EFFICIENCY and SUPPLY CURRENT vs. LOAD CURRENT 9

630 560

EFFICIENCY and SUPPLY CURRENT vs. LOAD CURRENT 10

700

A: MAX1044 with BOOST = V+ B: ICL7660 C: MAX1044 with BOOST = OPEN

-7

LOAD CURRENT (mA)

80 EFFICIENCY (%)

560

-8

B

LOAD CURRENT (mA)

90

30

B

A

OUTPUT VOLTAGE

LOAD CURRENT (mA)

100

EFFICIENCY (%)

-2.5

-1.0

B A

-3.0

-9

640

A: MAX1044 with BOOST = V+ B: ICL7660 C: MAX1044 with BOOST = OPEN

-3.5

-10

720

OUTPUT RIPPLE (mVp-p)

200

-4.0

800

MAX1044-Fig 8

-1.0

250

A

SUPPLY CURRENT (mA)

300 A: MAX1044 with BOOST = V+ B: ICL7660 C: MAX1044 with BOOST = OPEN

OUTPUT VOLTAGE

OUTPUT VOLTAGE (V)

-4.5

OUTPUT RIPPLE (mVp-p)

-5.0

350

MAX1044-Fig 2

MAX1044-Fig 1

-1.5

400

OUTPUT VOLTAGE (V)

OUTPUT VOLTAGE (V)

OUTPUT VOLTAGE

OUTPUT RIPPLE (mVp-p)

-2.0

OUTPUT VOLTAGE and OUTPUT RIPPLE vs. LOAD CURRENT

OUTPUT VOLTAGE and OUTPUT RIPPLE vs. LOAD CURRENT

MAX1044-Fig 3

OUTPUT VOLTAGE and OUTPUT RIPPLE vs. LOAD CURRENT

10,000 100,000

1

2

3

4

5

6

7

8

9

10

SUPPLY VOLTAGE (V)

_______________________________________________________________________________________

3

MAX1044/ICL7660

__________________________________________Typical Operating Characteristics (V+ = 5V; CBYPASS = 0.1µF; C1 = C2 = 10µF; LV = open; OSC = open; TA = +25°C; unless otherwise noted.)

____________________________Typical Operating Characteristics (continued) (V+ = 5V; CBYPASS = 0.1µF; C1 = C2 = 10µF; LV = open; OSC = open; TA = +25°C; unless otherwise noted.)

OSCILLATOR FREQUENCY vs. TEMPERATURE

QUIESCENT CURRENT vs. OSCILLATOR FREQUENCY

A 60

40

20

-25

0

25

50

75

MAX1044-Fig 11

USING EXTERNAL HCMOS OSCILLATOR

10

1 100

D A: MAX1044, BOOST = V+, LV = GND B: MAX1044, BOOST = V+, LV = OPEN C: ICL7660 and MAX1044 with BOOST = OPEN, LV = GND; ABOVE 5V, MAX1044 ONLY D: ICL7660 and MAX1044 with BOOST = OPEN, LV = OPEN

4

5

6

7

8

9

MAX1044 with BOOST = V+

300

200

100

ICL7660, MAX1044 with BOOST = OPEN

0 -50

10

OUTPUT RESISTANCE (Ω)

140 120 100 80 60

100

20 103

104

105

100 125

70 60

ICL7660, MAX1044 with BOOST = OPEN

50 40 MAX1044 with BOOST = V+

30

0 102

75

80

MAX1044-Fig 15

MAX1044-Fig 14

160

40

FREQUENCY (Hz)

4

180

200

0 101

50

OUTPUT RESISTANCE vs. TEMPERATURE

200

OUTPUT RESISTANCE (Ω)

300

C1, C2 = 1µF

400

C1, C2 = 10µF

500

C1, C2 = 100µF

700 600

25

OUTPUT RESISTANCE vs. SUPPLY VOLTAGE

OUTPUT RESISTANCE vs. OSCILLATOR FREQUENCY EXTERNAL HCMOS OSCILLATOR

0

TEMPERATURE (°C)

SUPPLY VOLTAGE (V)

1000

-25

MAX1044-Fig 16

3

MAX1044-Fig 13

MAX1044-Fig 12

400

10

800

105 5x105

500

C

900

104

QUIESCENT CURRENT vs. TEMPERATURE

100

2

103

QUIESCENT CURRENT vs. SUPPLY VOLTAGE

A B

0.1

102

OSCILLATOR FREQUENCY (Hz)

1000

1

101

TEMPERATURE (°C)

2000

1

USING EXTERNAL CAPACITOR

100

100 125

QUIESCENT CURRENT (µA)

C

1000

B

0 -50

QUIESCENT CURRENT (µA)

QUIESCENT CURRENT (µA)

A: MAX1044 with BOOST = V+ B: ICL7600 C: MAX1044 with BOOST = OPEN

80

10,000

MAX1044-Fig 10

OSCILLATOR FREQUENCY (kHz)

100

RESISTANCE (Ω)

MAX1044/ICL7660

Switched-Capacitor Voltage Converters

1

2

3

4

5

6

7

SUPPLY VOLTAGE (V)

8

9

10

20 -60 -40 -20 0

20 40 60 80 100 120 140

TEMPERATURE (°C)

_______________________________________________________________________________________

Switched-Capacitor Voltage Converters

PIN

NAME

FUNCTION

BOOST (MAX1044)

Frequency Boost. Connecting BOOST to V+ increases the oscillator frequency by a factor of six. When the oscillator is driven externally, BOOST has no effect and should be left open.

N.C. (ICL7660)

No Connection

1

2

CAP+

Connection to positive terminal of Charge-Pump Capacitor

3

GND

Ground. For most applications, the positive terminal of the reservoir capacitor is connected to this pin.

4

CAP-

Connection to negative terminal of Charge-Pump Capacitor

5

VOUT

Negative Voltage Output. For most applications, the negative terminal of the reservoir capacitor is connected to this pin.

6

LV

7

OSC

8

V+

Low-Voltage Operation. Connect to ground for supply voltages below 3.5V. ICL7660: Leave open for supply voltages above 5V. Oscillator Control Input. Connecting an external capacitor reduces the oscillator frequency. Minimize stray capacitance at this pin. Power-Supply Positive Voltage Input. (1.5V to 10V). V+ is also the substrate connection.

V+ V+

BOOST

MAX1044 CAP+ ICL7660

CBYPASS = 0.1µF EXTERNAL OSCILLATOR

OSC COSC

C1 10µF GND

LV

CAP-

VOUT

RL

VOUT C2 10µF

Figure 1. Maxim MAX1044/ICL7660 Test Circuit

_______________Detailed Description The MAX1044/ICL7660 are charge-pump voltage converters. They work by first accumulating charge in a bucket capacitor and then transfer it into a reservoir capacitor. The ideal voltage inverter circuit in Figure 2 illustrates this operation.

During the first half of each cycle, switches S1 & S3 close and switches S2 & S4 open, which connects the bucket capacitor C1 across V+ and charges C1. During the second half of each cycle, switches S2 & S4 close and switches S1 & S3 open, which connects the positive terminal of C1 to ground and shifts the negative terminal to VOUT. 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 voltages across them are equal. During successive cycles, C1 will continue pouring charge into C2 until the voltage across C2 reaches - (V+). In an actual voltage inverter, the output is less than - (V+) since the switches S1–S4 have resistance and the load drains charge from C2. Additional qualities of the MAX1044/ICL7660 can be understood by using a switched-capacitor circuit model. Switching the bucket capacitor, C1, between the input and output of the circuit synthesizes a resistance (Figures 3a and 3b.) When the switch in Figure 3a is in the left position, capacitor C1 charges to V+. When the switch moves to the right position, C1 is discharged to VOUT . The charge transferred per cycle is: ∆Q = C1(V+ - VOUT). If the switch is cycled at frequency f, then the resulting

_______________________________________________________________________________________

5

MAX1044/ICL7660

_____________________________________________________________ Pin Description

S1

current is: I = f x ∆Q = f x C1(V+ - VOUT). Rewriting this equation in Ohm’s law form defines an equivalent resistance synthesized by the switched-capacitor circuit where:

S2

V+

(V+ - VOUT ) 1 / (f x C1) and 1 REQUIV = f x C1

I=

C1

S3

C2

S4

VOUT = -(V+)

where f is one-half the oscillator frequency. This resistance is a major component of the output impedance of switched-capacitor circuits like the MAX1044/ICL7660. As shown in Figure 4, the MAX1044/ICL7660 contain MOSFET switches, the necessary transistor drive circuitry, and a timing oscillator.

Figure 2. Ideal Voltage Inverter

________________Design Information f V+

VOUT

C1

C2

RLOAD

The MAX1044/ICL7660 are designed to provide a simple, compact, low-cost solution where negative or doubled supply voltages are needed for a few lowpower components. Figure 5 shows the basic negative voltage converter circuit. For many applications, only two external capacitors are needed. The type of capacitor used is not critical.

Proper Use of the Low-Voltage (LV) Pin Figure 4 shows an internal voltage regulator inside the MAX1044/ICL7660. Use the LV pin to bypass this regulator, in order to improve low-voltage performance

Figure 3a. Switched Capacitor Model

VOUT 1 f × C1

BOOST pin 1 OSC pin 7

C2

6

S3

S4

Q

RLOAD LV pin 6

Figure 3b. Equivalent Circuit

CAP+ pin 2 S2

Q

÷2

INTERNAL REGULATOR

V+ REQUIV =

V+ pin 8 S1

1M

REQUIV

OSCILLATOR

MAX1044/ICL7660

Switched-Capacitor Voltage Converters

GND pin 3

CAPpin 4

Figure 4. MAX1044 and ICL7660 Functional Diagram

_______________________________________________________________________________________

VOUT pin 5

Switched-Capacitor Voltage Converters

C1 10µF

2 3 4

V+

8

1

MAX1044 ICL7660

7 6

VOUT = -(V+)

1

V+

8

CBYPASS

*

C2 10µF

2

MAX1044

7

10µF 3

COSC

6 VOUT = -(V+)

5

4

5 10µF

*REQUIRED FOR V+ < 3.5V

Figure 5. Basic Negative Voltage Converter

Figure 6. Negative Voltage Converter with COSC and BOOST

and allow operation down to 1.5V. For low-voltage operation and compatibility with the industry-standard LTC1044 and ICL7660, the LV pin should be connected to ground for supply voltages below 3.5V and left open for supply voltages above 3.5V. The MAX1044’s LV pin can be grounded for all operating conditions. The advantage is improved low-voltage performance and increased oscillator frequency. The disadvantage is increased quiescent current and reduced efficiency at higher supply voltages. For Maxim’s ICL7660, the LV pin must be left open for supply voltages above 5V. When operating at low supply voltages with LV open, connections to the LV, BOOST, and OSC pins should be short or shielded to prevent EMI from causing oscillator jitter.

Figure 6 shows this connection. Higher frequency operation lowers output impedance, reduces output ripple, allows the use of smaller capacitors, and shifts switching noise out of the audio band. When the oscillator is driven externally, BOOST has no effect and should be left open. The BOOST pin should also be left open for normal operation.

Oscillator Frequency Considerations

Reducing the Oscillator Frequency Using COSC An external capacitor can be connected to the OSC pin to lower the oscillator frequency (Figure 6). Lower frequency operation improves efficiency at low load currents by reducing the IC’s quiescent supply current. It also increases output ripple and output impedance. This can be offset by using larger values for C1 and C2. Connections to the OSC pin should be short to prevent stray capacitance from reducing the oscillator frequency.

Oscillator Frequency Specifications The MAX1044/ICL7660 do not have a precise oscillator frequency. Only minimum values of 1kHz and 5kHz for the MAX1044 and a typical value of 10kHz for the ICL7660 are specified. If a specific oscillator frequency is required, use an external oscillator to drive the OSC pin.

Overdriving the OSC Pin with an External Oscillator Driving OSC with an external oscillator is useful when the frequency must be synchronized, or when higher frequencies are required to reduce audio interference. The MAX1044/ICL7660 can be driven up to 400kHz. The pump and output ripple frequencies are one-half the external clock frequency. Driving the MAX1044/ICL7660 at a higher frequency increases the ripple frequency and allows the use of smaller capacitors. It also increases the quiescent current. The OSC input threshold is V+ - 2.5V when V+ ≥ 5V, and is V+ / 2 for V+ < 5V. If the external clock does not swing all the way to V+, use a 10kΩ pull-up resistor (Figure 7).

Increasing Oscillator Frequency Using the BOOST Pin For the MAX1044, connecting the BOOST pin to the V+ pin raises the oscillator frequency by a factor of about 6.

The MAX1044/ICL7660 output voltage is not regulated. The output voltages will vary under load according to the output resistance. The output resistance is primarily

For normal operation, leave the BOOST and OSC pins of the MAX1044/ICL7660 open and use the nominal oscillator frequency. Increasing the frequency reduces audio interference, output resistance, voltage ripple, and required capacitor sizes. Decreasing frequency reduces quiescent current and improves efficiency.

Output Voltage Considerations

_______________________________________________________________________________________

7

MAX1044/ICL7660

CONNECTION FROM V+ TO BOOST

MAX1044/ICL7660

Switched-Capacitor Voltage Converters

V+

1 2 10µF

10kΩ REQUIRED FOR TTL CMOS or V+ TTL GATE

8

MAX1044 ICL7660

7

3

6

4

5

VOUT = -(V+) 10µF

switching noise and EMI may be generated. To reduce these effects: 1) Power the MAX1044/ICL7600 from a low-impedance source. 2) Add a power-supply bypass capacitor with low effective series resistance (ESR) close to the IC between the V+ and ground pins. 3) Shorten traces between the IC and the charge-pump capacitors. 4) Arrange the components to keep the ground pins of the capacitors and the IC as close as possible. 5) Leave extra copper on the board around the voltage converter as power and ground planes. This is easily done on a double-sided PC board.

Figure 7. External Clocking

a function of oscillator frequency and the capacitor value. Oscillator frequency, in turn, is influenced by temperature and supply voltage. For example, with a 5V input voltage and 10µF charge-pump capacitors, the output resistance is typically 50Ω. Thus, the output voltage is about -5V under light loads, and decreases to about -4.5V with a 10mA load current. Minor supply voltage variations that are inconsequential to digital circuits can affect some analog circuits. Therefore, when using the MAX1044/ICL7660 for powering sensitive analog circuits, the power-supply rejection ratio of those circuits must be considered. The output ripple and output drop increase under heavy loads. If necessary, the MAX1044/ICL7660 output impedance can be reduced by paralleling devices, increasing the capacitance of C1 and C2, or connecting the MAX1044’s BOOST pin to V+ to increase the oscillator frequency.

Inrush Current and EMI Considerations During start-up, pump capacitors C1 and C2 must be charged. Consequently, the MAX1044/ICL7660 develop inrush currents during start-up. While operating, short bursts of current are drawn from the supply to C1, and then from C1 to C2 to replenish the charge drawn by the load during each charge-pump cycle. If the voltage converters are being powered by a highimpedance source, the supply voltage may drop too low during the current bursts for them to function properly. Furthermore, if the supply or ground impedance is too high, or if the traces between the converter IC and charge-pump capacitors are long or have large loops,

8

Efficiency, Output Ripple, and Output Impedance The power efficiency of a switched-capacitor voltage converter is affected by the internal losses in the converter IC, resistive losses of the pump capacitors, and conversion losses during charge transfer between the capacitors. The total power loss is:

∑ PLOSS = PINTERNAL +PSWITCH +PPUMP LOSSES

LOSSES

+PCONVERSION

CAPACITOR LOSSES

LOSSES

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, frequency, and connections to the LV, BOOST, and OSC pins. The next two losses are associated with the output resistance of the voltage converter circuit. Switch losses occur because of the on-resistances 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: 2

+ PSWITCH = IOUT x ROUT

PPUMP CAPACITOR LOSSES

LOSSES

where: ROUT ≅

1 + (fOSC / 2) x C1

(

)

4 2RSWITCHES + ESRC1 + ESRC2 and fOSC is the oscillator frequency.

_______________________________________________________________________________________

Switched-Capacitor Voltage Converters

1 2 PCONV.LOSS =  C1  (V+ ) 2 − VOUT  +   2  1 2 C2  VRIPPLE − 2VOUT VRIPPLE   x fOSC / 2   2

Increasing Efficiency Efficiency can be improved by lowering output voltage ripple and output impedance. Both output voltage ripple and output impedance can be reduced by using large capacitors with low ESR. The output voltage ripple can be calculated by noting that the output current is supplied solely from capacitor C2 during one-half of the charge-pump cycle.   1 VRIPPLE ≅  + 2 x ESRC2  IOUT  2 x fOSC x C2  Slowing the oscillator frequency reduces quiescent current. The oscillator frequency can be reduced by connecting a capacitor to the OSC pin. Reducing the oscillator frequency increases the ripple voltage in the MAX1044/ICL7660. Compensate by increasing the values of the bucket and reservoir capacitors. For example, in a negative voltage converter, the pump frequency is around 4kHz or 5kHz. With the recommended 10µF bucket and reservoir capacitors, the circuit consumes about 70µA of quiescent current while providing 20mA of output current. Setting the

oscillator to 400Hz by connecting a 100pF capacitor to OSC reduces the quiescent current to about 15µA. Maintaining 20mA output current capability requires increasing the bucket and reservoir capacitors to 100µF. Note that lower capacitor values can be used for lower output currents. For example, setting the oscillator to 40Hz by connecting a 1000pF capacitor to OSC provides the highest efficiency possible. Leaving the bucket and reservoir capacitors at 100µF gives a maximum IOUT of 2mA, a no-load quiescent current of 10µA, and a power conversion efficiency of 98%.

General Precautions 1) Connecting any input terminal to voltages greater than V+ or less than ground may cause latchup. Do not apply any input sources operating from external supplies before device power-up. 2) Never exceed maximum supply voltage ratings. 3) Do not connect C1 and C2 with the wrong polarity. 4) Do not short V+ to ground for extended periods with supply voltages above 5.5V present on other pins. 5) Ensure that VOUT (pin 5) does not go more positive than GND (pin 3). Adding a diode in parallel with C2, with the anode connected to VOUT and cathode to LV, will prevent this condition.

________________Application Circuits Negative Voltage Converter Figure 8 shows a negative voltage converter, the most popular application of the MAX1044/ICL7660. Only two external capacitors are needed. A third power-supply bypass capacitor is recommended (0.1µF to 10µF)

V+ 1 1 2 C1 10µF

8

BOOST

7

MAX1044 ICL7660

3 4

8

V+ CBYPASS 0.1µF

2

MAX1044 ICL7660

7

3

6

4

5

VOUT = 2(V+) - 2VD

6 LV

VOUT = -(V+)

5

C1

C2

C2 10µF

Figure 8. Negative Voltage Converter with BOOST and LV Connections

Figure 9. Voltage Doubler

_______________________________________________________________________________________

9

MAX1044/ICL7660

The first term is the effective resistance from the switched-capacitor circuit. Conversion losses occur during the transfer of charge between capacitors C1 and C2 when there is a voltage difference between them. The power loss is:

MAX1044/ICL7660

Switched-Capacitor Voltage Converters

V+

V+

C1 10µF

1

8

1

2

7

2

3

MAX1044 ICL7660 LV

4

C3 LV

4

5

VOUT = -(V+)

7

MAX1044 ICL7660

3

C1

6

8

6 5 VOUT = 2(V+) - 2VD

VOUT = 1 V+ 2

C2 10µF

C2

Figure 10. Voltage Divider

Figure 11. Combined Positive and Negative Converter

capacitors for the doubled positive voltage. This circuit has higher output impedances resulting from the use of a common charge-pump driver.

Positive Voltage Doubler Figure 9 illustrates the recommended voltage doubler circuit for the MAX1044/ICL7660. To reduce the voltage drops contributed by the diodes (V D), use Schottky diodes. For true voltage doubling or higher output currents, use the MAX660.

Cascading Devices Larger negative multiples of the supply voltage can be obtained by cascading MAX1044/ICL7660 devices (Figure 12). The output voltage is nominally VOUT = -n(V+) where n is the number of devices cascaded. The output voltage is reduced slightly by the output resistance of the first device, multiplied by the quiescent current of the second, etc. Three or more devices can be cascaded in this way, but output impedance rises dramatically. For example, the output resistance of two cascaded MAX1044s is approximately five times the output resistance of a single voltage converter. A better solution may be an inductive switching regulator, such as the MAX755, MAX759, MAX764, or MAX774.

Voltage Divider The voltage divider shown in Figure 10 splits the power supply in half. A third capacitor can be added between V+ and VOUT.

Combined Positive Multiplication and Negative Voltage Conversion Figure 11 illustrates this dual-function circuit. Capacitors C1 and C3 perform the bucket and reservoir functions for generating the negative voltage. Capacitors C2 and C4 are the bucket and reservoir

1 2 10µF

4

V+

8

MAX1044 ICL7660

3

7 6

1

C4

1 2

10µF

5

8

MAX1044 ICL7660

3 4

7 6

2

10µF

1 2 10µF

8

MAX1044 ICL7660

3

5

4

6

3

10µF

Figure 12. Cascading MAX1044/ICL7660 for Increased Output Voltage 10

7

______________________________________________________________________________________

5

VOUT = -n(V+)

10µF

Switched-Capacitor Voltage Converters

1 2 C1

V+

8 7

MAX1044 ICL7660

3

6

4

ROUT =

5

ROUT (of MAX1044 or ICL7660) n (number of devices)

1

Shutdown Schemes 1

8

2 C1

7

MAX1044 ICL7660

3

VOUT = -(V+)

6

4

C2

5

n

Figures 14a–14c illustrate three ways of adding shutdown capability to the MAX1044/ICL7660. When using these circuits, be aware that the additional capacitive loading on the OSC pin will reduce the oscillator frequency. The first circuit has the least loading on the OSC pin and has the added advantage of controlling shutdown with a high or low logic level, depending on the orientation of the switching diode.

Figure 13. Paralleling MAX1044/ICL7660 to Reduce Output Resistance V+ 1

_Ordering Information (continued) 10kΩ REQUIRED FOR TTL V+ CMOS or

8

TTL GATE

1N4148 2 10µF

MAX1044 ICL7660

7

3

6

4

5 VOUT = -(V+) 10µF

a) V+

MAX1044 ICL7660

7

74HC03 OPEN-DRAIN OR 74LS03 OPEN-COLLECTOR NAND GATES

PART

TEMP. RANGE

MAX1044ESA MAX1044MJA ICL7660CPA ICL7660CSA ICL7660CUA ICL7660C/D ICL7660EPA ICL7660ESA ICL7660AMJA† ICL7660AMTV†

-40°C to +85°C -55°C to +125°C 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C -55°C to +125°C -55°C to +125°C

PIN-PACKAGE 8 SO 8 CERDIP** 8 Plastic DIP 8 SO 8 µMAX Dice* 8 Plastic DIP 8 SO 8 CERDIP** 8 TO-99**

* Contact factory for dice specifications. ** Contact factory for availability. † The Maxim ICL7660 meets or exceeds all “A” and “S” specifications.

b) V+

MAX1044 ICL7660

7

OUTPUT ENABLE 74HC126 OR 74LS126 TRI-STATE BUFFER

c) Figure 14a-14c. Shutdown Schemes for MAX1044/ICL7660 ______________________________________________________________________________________

11

MAX1044/ICL7660

Paralleling Devices Paralleling multiple MAX1044/ICL7660s reduces output resistance and increases current capability. As illustrated in Figure 13, each device requires its own pump capacitor C1, but the reservoir capacitor C2 serves all devices. The equation for calculating output resistance is:

MAX1044/ICL7660

Switched-Capacitor Voltage Converters __________________________________________________________Chip Topographies MAX1044 GND

CAP+

ICL7660 BOOST

V+

0.084" (2.1mm)

CAP+ 0.076" (1.930mm)

GND OSC

CAPCAPV+

LV V OUT

V OUT LV

OSC 0.060" (1.5mm)

0.076" (1.930mm)

TRANSISTOR COUNT: 72 SUBSTRATE CONNECTED TO V+

TRANSISTOR COUNT: 71 SUBSTRATE CONNECTED TO V+

________________________________________________________Package Information DIM

E

A A1 B C D E e H L α

H

INCHES MAX MIN 0.044 0.036 0.008 0.004 0.014 0.010 0.007 0.005 0.120 0.116 0.120 0.116 0.0256 0.198 0.188 0.026 0.016 6° 0°

MILLIMETERS MIN MAX 0.91 1.11 0.10 0.20 0.25 0.36 0.13 0.18 2.95 3.05 2.95 3.05 0.65 4.78 5.03 0.41 0.66 0° 6° 21-0036

D

C

α

A 0.127mm 0.004 in

e B

A1

8-PIN µMAX PACKAGE

L

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.

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Printed USA

is a registered trademark of Maxim Integrated Products.