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 hand-
sets. 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 combina-
tion 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 load-
ing (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 exter-
nal clock from 20kHz to 240kHz. This flexibility permits
users to optimize their designs based on noise, capaci-
tor 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.
____________________________Features
o
Dual Positive/Negative Regulated Outputs:
±5V
OUT
from 3V
IN
o
Output-Ready Indicator to Protect GaAsFET PAs
o
2.5V to 5.5V Input Voltage Range
o
Low-Noise Output Ripple: < 2mVp-p
o
Synchronizable Switching Frequency
o
Uses Only Small, Low-Cost Capacitors
o
0.1µA Independent Shutdown Controls
o
Adjustable Output Voltages
o
Small 16-Pin QSOP Package
MAX768
______________Ordering Information
PART
MAX768C/D
MAX768EEE
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
Dice*
16 QSOP
*Dice
are specified at T
A
= +25°C, DC parameters only.
Pin Configuration appears at end of data sheet.
Dual Mode is a trademark of Maxim Integrated Products.
__________Typical Operating Circuit
V
IN
(3.0V TO 5.5V)
C7
IN
POUT
V+
C3
C5
POSITIVE
OUTPUT
+5V
SYNC
PSHDN
NSHDN
C1+
C1
C1-
C2+
C2
C2-
________________________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
MAX768
V-
NOUT
RDY
SETN
GND
SETP
C4
C6 NEGATIVE
OUTPUT
-5V
OUTPUT-
READY
SIGNAL
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
Low-Noise, Dual-Output, Regulated Charge Pump
for GaAsFET, LCD, and VCO Supplies
MAX768
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
POUT to V+ ........................................................... -12V to +0.3V
Continuous Power Dissipation (T
A
= +70°C)
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
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
(V
IN
= +3V, SYNC = IN, SETN = SETP = GND,
NSHDN
=
PSHDN
= IN, T
A
= -40°C to +85°C, unless otherwise noted. Typical values
are at T
A
= +25°C. See Figure 2.) (Note 1)
PARAMETER
Input Voltage Range
Minimum Input Start-Up Voltage
Positive Output Voltage
Negative Output Voltage
Positive Output Voltage Adjustable Range
Negative Output Voltage Adjustable Range
Maximum POUT, NOUT Output Currents
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 V
IN
-
|
V
OUT
|
)
Line Regulation
Load Regulation
Output Voltage Noise
Shutdown/SYNC Logic-Low Input Threshold
Shutdown/SYNC Logic-High Input Threshold
SHUTDOWN
SHDN
Input Bias Current
Shutdown Supply Current
V
SHDN
= 3V
NSHDN
=
PSHDN
= SYNC = GND
0.1
0.1
2
10
µA
µA
2.0
I
LOAD
= 0
0mA < I
LOAD
< 5mA, V
IN
= 3.0V to 5.5V
0mA < I
LOAD
< 5mA, V
IN
= 3.0V to 5.5V
(Note 2)
(Note 3)
V
IN
= 3V, V
POUT
≥
4.81V, V
NOUT
≤
-4.82V
V
IN
= 3.0V
V
IN
= 5.5V
NSHDN
= GND
V
SYNC
= GND
2 x V
IN
-
|
V
OUT
|
V
IN
= 3V to 5.5V
I
POUT
= 0mA to 5mA,
I
NOUT
= 0mA to -5mA
C
POUT
= C
NOUT
= 10µF,
10kHz < f < 1MHz
POUT
NOUT
I
POUT
= I
NOUT
= 0.1mA
I
POUT
= I
NOUT
= 5mA
-0.12
4.81
-5.10
1.25
-11
5
0.8
1.5
0.3
0.45
20
420
0.0
0.06
1.2
1.7
0.4
900
0.12
0.12
0.80
1.4
CONDITIONS
MIN
3.0
2.5
5.00
-5.00
5.14
-4.82
11
-1.25
TYP
MAX
5.5
UNITS
V
V
V
V
V
V
mA
mA
mA
mA
mV
%/V
%/mA
mVp-p
V
V
2
_______________________________________________________________________________________
Low-Noise, Dual-Output, Regulated Charge Pump
for GaAsFET, LCD, and VCO Supplies
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= +3V, SYNC = IN, SETN = SETP = GND,
NSHDN
=
PSHDN
= IN, T
A
= -40°C to +85°C, unless otherwise noted. Typical values
are at T
A
= +25°C. See Figure 2.) (Note 1)
PARAMETER
SYNC
SYNC Frequency Range (external)
SYNC Duty Cycle (external)
Oscillator Frequency (internal)
SYNC Input Leakage Current
SET INPUT
Positive Set-Reference Voltage
Negative Set-Reference Voltage
I
POUT
= 0.1mA
I
NOUT
= 0.1mA
V
SETP
= V
SETN
= 1.3V
Percent of V
NOUT
, I
NOUT
= 5mA
I
SINK
= 2mA
V
RDY
= 10V
0.01
10
85
T
A
= +25°C
T
A
= -40°C to + 85°C
T
A
= +25°C
T
A
= -40°C to + 85°C
1.217
1.215
-1.270
-1.275
1.25
1.25
-1.25
-1.25
0.01
94
1.283
1.285
-1.230
-1.225
0.1
98
0.25
2
V
V
µA
%
V
µA
mA
SYNC = GND (divide by 4)
V
SYNC
= 3V
20
40
21.5
85
25
100
0.1
240
60
28.5
115
2
kHz
%
kHz
µA
CONDITIONS
MIN
TYP
MAX
UNITS
MAX768
RDY
OUTPUT
SETP, SETN Input Leakage Current
RDY
Output Threshold
Output Low Voltage
Output Off Current
Maximum Sink Current
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
IN
- dropout voltage.
Note 3:
Maximum output voltage range is from the negative reference voltage to -2 x V
IN
+ dropout voltage.
__________________________________________Typical Operating Characteristics
(SYNC = IN, T
A
= +25°C, unless otherwise noted.)
mV
RMS
OUTPUT VOLTAGE
vs. OUTPUT CURRENT
MAX768-TOC01
POUT OUTPUT VOLTAGE
vs. OUTPUT CURRENT
MAX768-TOC02
NOUT OUTPUT VOLTAGE vs.
OUTPUT CURRENT
-4.3
OUTPUT VOLTAGE (V)
-4.4
-4.5
IN = 3.0V
-4.6
-4.7
-4.8
ONLY NOUT LOADED
MAX768-TOC03
0.30
IN = 3.0V
OUTPUT VOLTAGE (mV
RMS
)
5.2
ONLY POUT LOADED
5.0
OUTPUT VOLTAGE (V)
4.8
IN = 3.0V
4.6
4.4
4.2
IN = 4.0V
-4.2
0.20
NOUT = -5V
POUT = +5V
0.10
-4.9
-5.0
0
5
10
15
20
25
30
0
5
10
15
20
IN = 4.0V
25
30
0
0
5
10
15
20
25
OUTPUT CURRENT (mA)
4.0
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
_______________________________________________________________________________________
3
Low-Noise, Dual-Output, Regulated Charge Pump
for GaAsFET, LCD, and VCO Supplies
MAX768
____________________________Typical Operating Characteristics (continued)
(SYNC = IN, T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT
vs. SYNC FREQUENCY
MAX768-TOC04
CHARGE-PUMP FREQUENCY
vs. SUPPLY VOLTAGE
MAX768-TOC05
CHARGE-PUMP FREQUENCY
vs. TEMPERATURE
V
IN
= 3.3V
CHARGE-PUMP FREQUENCY (kHz)
100
80
60
40
SYNC = GND
20
0
SYNC = IN
MAX768-TOC06
4
115
SYNC = IN
CHARGE-PUMP FREQUENCY (kHz)
100
85
70
55
40
SYNC = GND
25
10
120
SUPPLY CURRENT (mA)
3
V
IN
= 5.0V
2
1
V
IN
= 3.3V
0
0
40
80
120 160 200 240 280 320
SYNC FREQUENCY (kHz)
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
-55 -35 -15
5
25
45
65
85 105 125
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
SHDN SUPPLY CURRENT
vs. TEMPERATURE
MAX768-TOC07
SHDN SUPPLY CURRENT
vs. TEMPERATURE
MAX768-TOC08
SUPPLY CURRENT
vs. SUPPLY VOLTAGE (NO LOAD)
1.6
SUPPLY CURRENT (mA)
1.4
1.2
1.0
0.8
f = 25kHz
0.6
0.4
0.2
f = 100kHz
MAX768-TOC09
20
18
SHDN SUPPLY CURRENT (µA)
16
14
12
10
8
6
4
2
0
-40
-15
10
35
60
V
IN
= 3.3V
V
IN
= 5.0V
0.40
0.35
SHDN SUPPLY CURRENT (µA)
0.30
0.25
0.20
0.15
0.10
0.05
0
-0.05
V
IN
= 3.3V
-40
-15
10
35
60
V
IN
= 4.0V
V
IN
= 5.0V
1.8
0
85
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
SUPPLY VOLTAGE (V)
85
TEMPERATURE (°C)
TEMPERATURE (°C)
EFFICIENCY vs. LOAD CURRENT
(NOUT ONLY LOADED)
MAX768 TOC10
EFFICIENCY vs. OUTPUT CURRENT
(POUT ONLY LOADED)
MAX768 TOC11
EFFICIENCY vs. OUTPUT CURRENT
LOAD BETWEEN POUT AND NOUT
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
V
IN
= 4.0V
MAX768 TOC12
90
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
1
10
V
IN
= 4.0V
V
IN
= 3.0V
90
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
V
IN
= 4.0V
V
IN
= 3.0V
90
V
IN
= 3.0V
100
0.1
1
10
100
0.1
1
10
100
LOAD CURRENT (mA)
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
4
_______________________________________________________________________________________
Low-Noise, Dual-Output, Regulated Charge Pump
for GaAsFET, LCD, and VCO Supplies
_____________________________Typical Operating Characteristics (continued)
(SYNC = IN, T
A
= +25°C, unless otherwise noted.)
POUT MAXIMUM OUTPUT CURRENT
vs. SUPPLY VOLTAGE
MAX768-TOC13
MAX768
NOUT MAXIMUM OUTPUT CURRENT
vs. SUPPLY VOLTAGE
80
70
60
50
40
30
20
10
0
ONLY NOUT LOADED
MAX768-TOC14
140
ONLY POUT LOADED
MAXIMUM OUTPUT CURRENT (mA)
120
100
80
60
40
20
0
2.5
3.0
3.5
4.0
4.5
90
MAXIMUM OUTPUT CURRENT (mA)
5.0
2.5
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
TIME TO EXIT SHUTDOWN
MAX768-TOC15
+3V,
PSHDN = NSHDN
+5V, V
POUT
0V
-5V, V
NOUT
0V,
RDY
1ms/div
POUT OUTPUT NOISE AND RIPPLE
MAX768-TOC16
NOUT OUTPUT NOISE AND RIPPLE
MAX768-TOC17
V
POUT,
500µV/div
AC COUPLED
V
NOUT
, 500µV/div
AC COUPLED
500µs/div
POUT = +5V AT 5mA
IN = 3.0V
NOUT = -5V AT 5mA
IN = 3.0V
500µs/div
_______________________________________________________________________________________
5
