Rainbow Electronics MAX768 User Manual

19-1174; Rev 0; 12/96

Low-Noise, Dual-Output, Regulated Charge Pump

for GaAsFET, LCD, and VCO Supplies

_______________General Description

The MAX768 low-noise, dual-output, regulated charge
pump provides a negative output for biasing GaAsFET
power amplifiers, and a positive output for powering
voltage-controlled oscillators (VCOs) in wireless hand­sets. The outputs can also be used to power LCDs.
Output ripple is less than 2mVp-p. The MAX768 is
intended for use in low-voltage systems where a simple
charge-pump inverter is inadequate, or where the VCO
needs more range to improve its signal-to-noise ratio.
The input range is 2.5V to 5.5V, enabling direct power
from 1Li+ and 3-cell NiMH/NiCd batteries.

The MAX768 includes a voltage-doubler charge pump,
followed by an inverting charge pump. This combina­tion produces unregulated outputs that are ±2x the
input. Two internal low-dropout linear regulators provide
the low-noise, regulated positive and negative outputs.
Output current is guaranteed to be at least 5mA per
output. The linear regulators use CMOS devices, so the
quiescent current remains independent of output load­ing (even in dropout), and the dropout voltage
approaches zero with no load current.

The MAX768 has two preset switching frequencies
(25kHz or 100kHz), or can be synchronized by an exter­nal clock from 20kHz to 240kHz. This flexibility permits
users to optimize their designs based on noise, capaci­tor size, and quiescent-supply-current criteria.

The device features Dual Mode™ operation: the output
voltage is preset to +5V and -5V, or can be adjusted by
adding external resistor dividers. Other features include
independent shutdowns and a logic output that signals
when the negative voltage has risen to within 10% of its
regulation setpoint (to protect the power amplifier
GaAsFET). The MAX768 is available in a space-saving,
16-pin QSOP, which is the same size as a standard
8-pin SO.

________________________Applications

GaAsFET Power Amp Bias
Voltage-Controlled Oscillator (VCO) Supply
Tuner Diode Power Supply
Positive and Negative LCD Supply
Cellular Phone
PCS and Cordless Phone
Wireless Handsets
Wireless Handheld Computers
Wireless PCMCIA Cards
Modems

____________________________Features

♦ Dual Positive/Negative Regulated Outputs:

±5V

♦ Output-Ready Indicator to Protect GaAsFET PAs
♦ 2.5V to 5.5V Input Voltage Range
♦ Low-Noise Output Ripple: < 2mVp-p
♦ Synchronizable Switching Frequency
♦ Uses Only Small, Low-Cost Capacitors
♦ 0.1µA Independent Shutdown Controls
♦ Adjustable Output Voltages
♦ Small 16-Pin QSOP Package

OUT

from 3V

IN

______________Ordering Information

PART

MAX768C/D
MAX768EEE -40°C to +85°C

*

Dice are specified at TA= +25°C, DC parameters only.

Pin Configuration appears at end of data sheet.

Dual Mode is a trademark of Maxim Integrated Products.

TEMP. RANGE PIN-PACKAGE

0°C to +70°C

Dice*

16 QSOP

__________Typical Operating Circuit

VIN

(3.0V TO 5.5V)

C7

C5

C6

POSITIVE
OUTPUT
+5V

NEGATIVE
OUTPUT

-5V
OUTPUT-

READY
SIGNAL

SYNC
PSHDN
NSHDN
C1+

C1

C2

C1­C2+

C2-

IN

MAX768

GND

POUT

V+

C3

C4

V-

NOUT

RDY

SETPSETN

MAX768

________________________________________________________________

Maxim Integrated Products

1

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone]

Low-Noise, Dual-Output, Regulated Charge Pump
for GaAsFET, LCD, and VCO Supplies

ABSOLUTE MAXIMUM RATINGS

VIN, C1-, SYNC, PSHDN, NSHDN to GND...............-0.3V to +6V

V+, C1+, C2+, RDY to GND...................................-0.3V to +12V

SETP to GND .......................................................... -0.3V to +3V

SETN to GND............................................................-3V to +0.3V

V-, C2- to GND ...................................................... -12V to +0.3V

OUTP, OUTN Short Circuited to GND .......................Continuous

NOUT to V- ........................................................... -0.3V to +12V

MAX768

POUT to V+ ........................................................... -12V to +0.3V

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.

Continuous Power Dissipation (T

QSOP (derate 8.70mW/°C above +70°C)......................696mW

Operating Temperature Range

MAX768EEE.......................................................-40°C to +85°C

Maximum Junction Temperature .....................................+150°C

Storage Temperature Range.............................-65°C to +165°C

Lead Temperature (soldering, 10sec).............................+300°C

ELECTRICAL CHARACTERISTICS

(VIN= +3V, SYNC = IN, SETN = SETP = GND, NSHDN = PSHDN = IN, TA= -40°C to +85°C, unless otherwise noted. Typical values

= +25°C. See Figure 2.) (Note 1)

are at T

A

CONDITIONS

I

Minimum Input Start-Up Voltage

No-Load Supply Current at 100kHz
(both regulators active)

No-Load Supply Current at 100kHz
(negative regulator off)

No-Load Supply Current at 25kHz
(both regulators active)

Dropout Voltage (2 x VIN- |V

Output Voltage Noise

SHUTDOWN

SHDN Input Bias Current

OUT

)

|

= 0

LOAD

0mA < I
0mA < I
(Note 2)
(Note 3)
VIN= 3V, V
VIN= 3.0V
VIN= 5.5V 1.5

NSHDN = GND

V

SYNC

2 x VIN- | V
VIN= 3V to 5.5V

I

POUT

I

NOUT

C

POUT =CNOUT

10kHz < f < 1MHz

V

SHDN

NSHDN = PSHDN = SYNC = GND

< 5mA, VIN= 3.0V to 5.5V V4.81 5.00 5.14Positive Output Voltage

LOAD

< 5mA, VIN= 3.0V to 5.5V

LOAD

≥ 4.81V, V

POUT

= GND mA0.45 0.80

I

POUT

OUT

|

I

POUT

= 0mA to 5mA,
= 0mA to -5mA

=

10µF,

= 3V

NOUT

= I
= I

NOUT
NOUT

POUT
NOUT

≤ -4.82V

= 0.1mA
= 5mA

= +70°C)

A

0.8 1.4

20

420 900

1.2

1.7

UNITSMIN TYP MAXPARAMETER

%/mA0.06 0.12Load Regulation

mVp-p

V3.0 5.5Input Voltage Range
V2.5

V-5.10 -5.00 -4.82Negative Output Voltage
V1.25 11Positive Output Voltage Adjustable Range
V-11 -1.25Negative Output Voltage Adjustable Range

mA5Maximum POUT, NOUT Output Currents
mA

mA0.3

mV

%/V-0.12 0.0 0.12Line Regulation

V0.4Shutdown/SYNC Logic-Low Input Threshold
V2.0Shutdown/SYNC Logic-High Input Threshold

µA0.1 2
µA0.1 10Shutdown Supply Current

2 _______________________________________________________________________________________

Low-Noise, Dual-Output, Regulated Charge Pump

RDY

for GaAsFET, LCD, and VCO Supplies

ELECTRICAL CHARACTERISTICS (continued)

(VIN= +3V, SYNC = IN, SETN = SETP = GND, NSHDN = PSHDN = IN, TA= -40°C to +85°C, unless otherwise noted. Typical values

= +25°C. See Figure 2.) (Note 1)

are at T

A

CONDITIONS

SYNC

Oscillator Frequency (internal)

SYNC = GND (divide by 4)
V

= 3V

SYNC

SET INPUT

Positive Set-Reference Voltage

Negative Set-Reference Voltage

I

POUT

I

NOUT

V

SETP

= 0.1mA

= 0.1mA

= V

SETN

TA= +25°C
TA= -40°C to + 85°C
TA= +25°C
TA= -40°C to + 85°C

= 1.3V

OUTPUT

RDY Output Threshold

Percent of V
I

= 2mA V0.25Output Low Voltage

SINK

V

= 10V

RDY

NOUT

, I

NOUT

= 5mA

Note 1: Parameters to -40°C are guaranteed by design, not production tested.
Note 2: Maximum output voltage range is from the positive reference voltage to 2 x V
Note 3: Maximum output voltage range is from the negative reference voltage to -2 x V

21.5 25 28.5
85 100 115

1.217 1.25 1.283

1.215 1.25 1.285

-1.270 -1.25 -1.230

-1.275 -1.25 -1.225

- dropout voltage.

IN

+ dropout voltage.

IN

UNITSMIN TYP MAXPARAMETER

MAX768

kHz20 240SYNC Frequency Range (external)

%40 60SYNC Duty Cycle (external)

kHz

µA0.1 2SYNC Input Leakage Current

V

V

µA0.01 0.1SETP, SETN Input Leakage Current

%85 94 98

µA0.01 2Output Off Current

mA10Maximum Sink Current

__________________________________________Typical Operating Characteristics

(SYNC = IN, TA = +25°C, unless otherwise noted.)

mV

OUTPUT VOLTAGE

RMS

0.30

)

RMS

0.20

0.10

OUTPUT VOLTAGE (mV

0

vs. OUTPUT CURRENT

IN = 3.0V

NOUT = -5V

POUT = +5V

0 5 15 25

10 20

OUTPUT CURRENT (mA)

_______________________________________________________________________________________ 3

5.2

MAX768-TOC01

5.0

4.8

4.6

4.4

OUTPUT VOLTAGE (V)

4.2

4.0

POUT OUTPUT VOLTAGE 

vs. OUTPUT CURRENT

ONLY POUT LOADED

0 5 15 30





10 20 25

OUTPUT CURRENT (mA)

IN = 4.0V

IN = 3.0V

-4.2

-4.3

MAX768-TOC02

-4.4

-4.5

-4.6

-4.7

OUTPUT VOLTAGE (V)

-4.8

-4.9

-5.0

NOUT OUTPUT VOLTAGE vs. 

OUTPUT CURRENT

ONLY NOUT LOADED

0 5 15 30

OUTPUT CURRENT (mA)





IN = 3.0V

IN = 4.0V

10 20 25

MAX768-TOC03

Low-Noise, Dual-Output, Regulated Charge Pump
for GaAsFET, LCD, and VCO Supplies

____________________________Typical Operating Characteristics (continued)

(SYNC = IN, TA = +25°C, unless otherwise noted.)

4

MAX768

3

2

SUPPLY CURRENT (mA)

1

0

0 40 120 320

SHDN SUPPLY CURRENT

20

vs. SYNC FREQUENCY

18
16
14
12
10

SHDN SUPPLY CURRENT (µA)

90
80
70
60
50
40

EFFICIENCY (%)

30
20
10

0

V

IN

8
6

4
2
0

-40 -15 35 85

EFFICIENCY vs. LOAD CURRENT

(NOUT ONLY LOADED)

V

IN

0.1 1 10 100
LOAD CURRENT (mA)

SUPPLY CURRENT

VIN = 5.0V

V

= 3.3V

IN

16080 200 240 280

SYNC FREQUENCY (kHz)

vs. TEMPERATURE

= 5.0V

V

= 3.3V

IN

TEMPERATURE (°C)

= 3.0V

V

= 4.0V

IN

CHARGE-PUMP FREQUENCY

115

100

MAX768-TOC04

85

70

55

40

CHARGE-PUMP FREQUENCY (kHz)

25

10

0.40

0.35

MAX768-TOC07

0.30

0.25

0.20

0.15

0.10

SHDN SUPPLY CURRENT (µA)

0.05
0

MAX768 TOC10

EFFICIENCY (%)

-0.05

90
80
70
60
50
40
30
20
10

0

6010

vs. SUPPLY VOLTAGE

SYNC = IN

SYNC = GND

2.5 3.0 4.0 6.0

SHDN SUPPLY CURRENT

-40 -15 35 85

EFFICIENCY vs. OUTPUT CURRENT

(POUT ONLY LOADED)

V

IN

0.1 1 10 100
OUTPUT CURRENT (mA)

4.53.5 5.0 5.5

SUPPLY VOLTAGE (V)

vs. TEMPERATURE

V

IN

TEMPERATURE (°C)

= 3.0V

V

= 4.0V

IN

= 5.0V

V

IN

V

IN

= 4.0V
= 3.3V

6010

120

MAX768-TOC05

100

CHARGE-PUMP FREQUENCY (kHz)

MAX768-TOC08

SUPPLY CURRENT (mA)

MAX768 TOC11

EFFICIENCY (%)

CHARGE-PUMP FREQUENCY

vs. TEMPERATURE

V

= 3.3V

IN

SYNC = IN

80

60

40

20

0

-55 -35 5 125

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2
0

2.5 3.0 4.0 6.0

90
80
70
60
50
40
30
20
10

0

0.1 1 10 100

SYNC = GND

25-15 45 8565 105

TEMPERATURE (°C)

SUPPLY CURRENT

vs. SUPPLY VOLTAGE (NO LOAD)

f = 100kHz

f = 25kHz

SUPPLY VOLTAGE (V)

EFFICIENCY vs. OUTPUT CURRENT

LOAD BETWEEN POUT AND NOUT

V

= 3.0V

IN

OUTPUT CURRENT (mA)

5.04.5 5.53.5

V

= 4.0V

IN

MAX768-TOC06

MAX768-TOC09

MAX768 TOC12

4 _______________________________________________________________________________________