For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
General Description
The MAX1747 triple charge-pump DC-DC converter
provides the regulated voltages required by active
matrix thin-film transistor (TFT) liquid-crystal displays
(LCDs) in a low-profile TSSOP package. One high-
power and two low-power charge pumps convert the
+2.7V to +4.5V input supply voltage into three indepen-
dent output voltages.
The primary high-power charge pump generates an
output voltage (VOUT) between 4.5V and 5.5V that is
regulated within ±1%. The low-power BiCMOS control
circuitry and the low on-resistance (RON) power
MOSFETs maximize efficiency. The adjustable switch-
ing frequency (200kHz to 2MHz) provides fast transient
response and allows the use of small low-profile ceram-
ic capacitors.
The dual low-power charge pumps independently regu-
late one positive output (VPOS) and one negative output
(VNEG). These additional outputs use external diode
and capacitor multiplier stages (as many stages as
required) to regulate output voltages up to +35V and
-35V.
The constant switching frequency and a proprietary
regulation algorithm minimize output ripple and capaci-
tor sizes for all three charge pumps. The MAX1747 is
available in the ultra-thin TSSOP package (1.1mm max
height).
MAX1747
Triple Charge-Pump TFT LCD
DC-DC Converter
________________________________________________________________ Maxim Integrated Products 1
20
19
18
17
16
15
14
13
1
2
3
4
5
6
7
8
OUT
CXP
SUPM
CXNFB
RDY
TGND
TGND
TOP VIEW
PGND
SUPP
DRVP
SUPNREF
GND
IN
INTG
12
11
9
10
DRVN
SHDNFBN
FBP
MAX1747
TSSOP
Pin Configuration
19-1788; Rev 0; 10/00
Ordering Information
PART TEMP. RANGE PIN-PACKAGE
MAX1747EUP -40°C to +85°C 20 TSSOP
Features
♦Adjustable Outputs
Up to +5.5V Main High-Power Output
Up to +35V Positive Charge-Pump Output
Down to -35V Negative Charge-Pump Output
♦200kHz to 2MHz Adjustable Switching Frequency
♦+2.7V to +4.5V Input Supply
♦Internal Power MOSFETs
♦0.1µA Shutdown Current
♦Internal Soft-Start
♦Power-Ready Output
♦Internal Supply Sequencing
♦Fast Transient Response
♦Ultra-Thin Solution (No Inductors)
♦Thin TSSOP Package (1.1mm max)
Applications
TFT Active-Matrix LCDs
Passive-Matrix Displays
Personal Digital Assistants (PDAs)
IN
FB
SUPN
DRVP
FBP
PGND
DRVN
GND
TGND
MAX1747
SHDN
RDY
FBN
REF
INPUT
TO µC
SUPM
MAIN OUTPUT
POSITIVE
OUTPUT
INTG
CXP
CXN
OUT
SUPP
NEGATIVE
OUTPUT
Typical Operating Circuit
EVALUATION KIT
AVAILABLE
MAX1747
Triple Charge-Pump TFT LCD
DC-DC Converter
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN = VSUPM = +3.0V, VSUPP = VSUPN = +5V, TGND = PGND = GND, I SHDN = 22µA, COUT = 2 ✕4.7µF, CREF = 0.22µF, CINTG =
1500pF, VOUT = +5V, TA= 0°C to +85°C,unless otherwise noted. Typical values are at TA= +25°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.
IN, SUPM, OUT, TGND to GND................................-0.3V to +6V
SHDN........................................................................-0.3V to +1V
PGND to GND.....................................................................±0.3V
SUPM to IN .........................................................................±0.3V
CXN to PGND.........................................-0.3V to (VSUPM + 0.3V)
CXP to PGND ............................(VSUPM - 0.3V) to (VOUT + 0.3V)
DRVN to GND .........................................-0.3V to (VSUPN + 0.3V)
DRVP to GND..........................................-0.3V to (VSUPP + 0.3V)
RDY to GND ...........................................................-0.3V to +14V
SUPP, SUPN to GND..............................................-0.3V to +14V
INTG, REF, FB, FBN, FBP to GND...............-0.3V to (VIN + 0.3V)
Continuous Current into:
SUPM, CXN, CXP, OUT ..............................................±800mA
SUPP, SUPN, DRVN, DRVP........................................±200mA
SHDN...........................................................................+100µA
All Other Pins ....................................................................±10mA
Continuous Power Dissipation (TA= +70°C)
20-Pin TSSOP (derate 10.9mW/°C above +70°C) .......879mW
Operating Temperature Range............................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX U N IT S
Input Supply Range VIN 2.7 4.5 V
Input Undervoltage Threshold VUVLO VIN falling, 40mV hysteresis (typ) 2.2 2.4 2.6 V
Input Quiescent Supply
Current
IIN +
ISUPM
VFB = VFBP = 1.5V, VFBN = -0.2V, VOUT = 5V,
no load on DRVN and DRVP; CXN
and CXP open
0.9 1.0 mA
Output Quiescent Supply
Current IQ
(
OUT
)
VFB = VFBP = 1.5V, VFBN = -0.2V, VOUT = 5V,
no load on DRVN and DRVP; CXN and
CXP open
2.5 4.0 mA
Shutdown Supply Current V
SHDN = 0, VSUPM = 5V 0.1 20 µA
Operating Frequency fOSC I
SHDN = 22µA 0.65 1 1.2 MHz
MAIN CHARGE PUMP
Output Voltage Range VOUT 4.5 5.5 V
Maximum Output Current IOU T
(
M AX
)
CX = 0.47µF 200 mA
FB Regulation Voltage VFB 1.237 1.248 1.263 V
FB Input Bias Current IFB VFB = 1.25V -50 +50 nA
Integrator Transconductance 530 µS
FB Power-Ready Trip Level Rising edge 1.09 1.125 1.16 V
FB Fault Trip Level Falling edge 1.100 V
Main Soft-Start Period 4.096
/ FOSC s
NEGATIVE LOW-POWER CHARGE PUMP
SUPN Input Supply Range VSUPN 2.7 13 V
SUPN Quiescent Current ISUPN VFBN = -0.2V, no load on DRVN 0.6 0.8 mA
SUPN Shutdown Current V
SHDN = 0, VSUPN = 13V 0.1 10 µA
FBN Regulation Voltage VFBN -50 0 +50 mV
MAX1747
Triple Charge-Pump TFT LCD
DC-DC Converter
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VSUPM = +3.0V, VSUPP = VSUPN = +5V, TGND = PGND = GND, I SHDN = 22µA, COUT = 2 ✕4.7µF, CREF = 0.22µF, CINTG =
1500pF, VOUT = +5V, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX U N IT S
FBN Input Bias Current IFBN VFBN = -50mV -50 +50 nA
DRVN PCH On-Resistance 36Ω
VFBN = 50mV 1 5 Ω
DRVN NCH On-Resistance VFBN = -50mV 20 kΩ
FBN Power-Ready Trip Level Falling edge 80 125 165 mV
FBN Fault Trip Level Rising edge 140 mV
Negative Soft-Start Period 2.048/
FOSC s
POSITIVE LOW-POWER CHARGE PUMP
SUPP Input Supply Range VSUPP 2.7 13 V
SUPP Quiescent Current ISUPP VFBP = 1.5V, no load on DRVP 0.6 0.8 mA
SUPP Shutdown Current V
SHDN = 0, VSUPP = 13V 0.1 10 µA
FBP Regulation Voltage VFBP 1.20 1.25 1.30 V
FBP Input Bias Current IFBP VFBP = 1.5V -50 +50 nA
DRVP PCH On-Resistance 36Ω
VFBP = 1.20V 1.5 5 Ω
DRVP NCH On-Resistance VFBP = 1.30V 20 kΩ
FBP Power-Ready Trip Level Rising edge 1.090 1.125 1.160 V
FBP Fault Trip Level Falling edge 1.100 V
Positive Soft-Start Period 2.048/
FOSC s
REFERENCE
Reference Voltage VREF -2µA < IREF < 50µA 1.231 1.25 1.269 V
Reference Undervoltage
Threshold VREF rising 0.95 1.05 1.18 V
LOGIC SIGNALS
SHDN Input Low Voltage 0.4 V
SHDN Bias Voltage I
SHDN = 22µA 580 724 830 mV
SHDN Bias Voltage Tempco 2 mV/°C
SHDN Input Current Range I
SHDN For 200kHz to 2MHz operation 3 65 µA
RDY Output Low Voltage ISINK = 2mA 0.25 0.5 V
RDY Output High Leakage V
RDY = 13V 0.01 1 µA
MAX1747
Triple Charge-Pump TFT LCD
DC-DC Converter
4 _______________________________________________________________________________________
PARAMETER SYMBOL CONDITIONS MIN MAX UNITS
Input Supply Range VIN 2.7 4.5 V
Input Undervoltage Threshold VUVLO VIN falling, 40mV hysteresis (typ) 2.2 2.6 V
Input Quiescent Supply
Current
IIN +
ISUPM
VFB = VFBP = 1.5V, VFBN = -0.2V, VOUT = 5V,
no load on DRVN and DRVP; CXN and
CXP open
1.0 mA
Output Quiescent Supply
Current IQ(OUT)
VFB = VFBP = 1.5V, VFBN = -0.2V, VOUT = 5V,
no load on DRVN and DRVP; CXN and
CXP open
4.0 mA
Input Shutdown Current V
SHDN = 0, VSUPM = 5V 20 µA
Operating Frequency fOSC I
SHDN = 22µA 0.65 1.2 MHz
MAIN CHARGE PUMP
Output Voltage Range VOUT 4.5 5.5 V
Output Current IOU T
(
M AX
)
CX = 0.47µF 200 mA
FB Regulation Voltage VFB 1.222 1.271 V
FB Input Bias Current IFB VFB = 1.25V -50 +50 nA
FB Power-Ready Trip Level Rising edge 1.09 1.16 V
NEGATIVE LOW-POWER CHARGE PUMP
SUPN Input Supply Range VSUPN 2.7 13 V
SUPN Quiescent Current ISUPN VFBN = -0.2V, no load on DRVN 0.8 mA
SUPN Shutdown Current V
SHDN = 0, VSUPN = 13V 10 µA
FBN Regulation Voltage VFBN -50 +50 mV
FBN Input Bias Current IFBN VFBN = 0 -50 +50 nA
DRVN PCH On-Resistance 6Ω
VFBN = 50mV 5 Ω
DRVN NCH On-Resistance VFBN = -50mV 20 kΩ
FBN Power-Ready Trip Level Falling edge 80 165 mV
POSITIVE LOW-POWER CHARGE PUMP
SUPP Input Supply Range VSUPP 2.7 13 V
SUPP Quiescent Current ISUPP VFBP = 1.5V, no load on DRVP 0.8 mA
SUPP Shutdown Current V
SHDN = 0, VSUPP = 13V 10 µA
FBP Regulation Voltage VFBP 1.20 1.30 V
FBP Input Bias Current IFBP VFBP = 1.5V -50 +50 nA
DRVP PCH On-Resistance 6Ω
VFBP = 1.20V 5 Ω
DRVP NCH On-Resistance VFBP = 1.30V 20 kΩ
FBP Power-Ready Trip Level Rising edge 1.09 1.16 V
ELECTRICAL CHARACTERISTICS
(VIN = VSUPM = +3.0V, VSUPP = VSUPN = +5V, TGND = PGND = GND, ISHDN = 22µA, COUT = 2 ✕4.7µF, CREF = 0.22µF, CINTG =
1500pF, VOUT = +5V, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)
MAX1747
Triple Charge-Pump TFT LCD
DC-DC Converter
_______________________________________________________________________________________ 5
PARAMETER SYMBOL CONDITIONS MIN MAX UNITS
REFERENCE
Reference Voltage VREF -2µA < IREF < 50µA 1.222 1.269 V
Reference Undervoltage
Threshold VREF rising 0.95 1.18 V
LOGIC SIGNALS
SHDN Input Low Voltage 0.4 V
SHDN Bias Voltage I
SHDN = 22µA 580 900 mV
SHDN Input Current Range I
SHDN For 200kHz to 2MHz operation 3 65 µA
RDY Output Low Voltage ISINK = 2mA 0.5 V
RDY Output High Leakage V
RDY = 13V 1 µA
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VSUPM = +3.0V, VSUPP = VSUPM = +5V, TGND = PGND = GND, ISHDN = 22µA, COUT = 2 ✕4.7µF, CREF = 0.22µF, CINTG =
1500pF, VOUT = +5V, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)
Note 1: Specifications from 0°C to -40°C are guaranteed by design, not production tested.
Typical Operating Characteristics
(Circuit of Figure 1, VIN = VSUPM = +3.3V, TA= +25°C, unless otherwise noted.)
4.97
4.99
4.98
5.01
5.00
5.02
5.03
0200100 300 400
MAX1747 toc01
IOUT (mA)
VOUT (V)
MAIN OUTPUT EFFICIENCY
vs. LOAD CURRENT
(MAIN CHARGE PUMP ONLY)
VIN = 3.3V
VIN = 4.0V
VIN = 2.8V
40
60
50
80
70
90
100
0200100 300 400
MAX1747 toc02
IOUT (mA)
EFFICIENCY (%)
MAIN OUTPUT EFFICIENCY
vs. LOAD CURRENT
(MAIN CHARGE PUMP ONLY)
VOUT = 5V
VIN = 3.3V
VIN = 4.0V
VIN = 2.8V
40
60
50
80
70
90
100
0200100 300 400
MAX1747 toc03
IOUT (mA)
EFFICIENCY (%)
MAIN OUTPUT EFFICIENCY
vs. LOAD CURRENT
(MAIN CHARGE PUMP ONLY)
VOUT = 5V
VIN = 3.3V
VIN = 4.0V
VIN = 2.8V
VNEG = -7V WITH INEG = 10mA
VPOS = 12V WITH IPOS = 5mA
MAX1747
Triple Charge-Pump TFT LCD
DC-DC Converter
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = VSUPM = +3.3V, TA= +25°C, unless otherwise noted.)
0
2
4
6
8
10
12
14
16
0 0.5 1.0 1.5 2.0
NO-LOAD SUPPLY CURRENT
vs. SWITCHING FREQUENCY
MAX1747 toc04
FREQUENCY (MHz)
ICC + IIN (mA)
0
0.4
1.2
0.8
1.6
2.0
02010 30 40 50
SWITCHING FREQUENCY
vs. ISHDN
MAX1747 toc05
ISHDN (mA)
FREQUENCY (MHz)
9.0
10.0
9.5
11.0
10.5
11.5
12.0
-40 10-15 35 60 85
MAX1747 toc06
TEMPERATURE (°C)
IIN + ISUPM (mA)
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
VON = 3.3V
RFREQ = 120kΩ
0.85
0.95
0.90
1.05
1.00
1.10
1.15
-40 10-15 356085
MAX1747 toc07
TEMPERATURE (°C)
FREQUENCY (MHz)
SWITCHING FREQUENCY
vs. TEMPERATURE
VON = 3.3V
RFREQ = 120kΩ
20
30
40
50
60
70
80
90
100
0 10203040
NEGATIVE LOW-POWER CHARGE-PUMP
EFFICIENCY vs. LOAD CURRENT
MAX1747 toc08
INEG (mA)
EFFICIENCY (%)
VSUPN = 6V
VSUPN = 5V
VSUPN = 7V
VNEG = -7V
-7.1
-7.0
-6.9
-6.8
-6.7
-6.6
-6.5
-6.4
-6.3
0 10203040
NEGATIVE LOW-POWER CHARGE-PUMP
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX1747 toc09
INEG (mA)
VNEG (V)
VSUPN = 5V
VSUPN = 6V
VSUPN = 7V
-22
-18
-10
-14
-6
-2
37591113
MAXIMUM NEGATIVE CHARGE-PUMP
OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
MAX1747 toc10
VSUPN (V)
VNEG (V)
INEG = 10mA
INEG = 1mA
VNEG(NOMINAL) = -20V
11.4
11.5
11.6
11.7
11.8
11.9
12.0
12.1
12.2
0 10203040
POSITIVE LOW-POWER CHARGE-PUMP
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX1747 toc12
IPOS (mA)
VPOS (V)
VSUPP = 7V
VSUPP = 6V
VSUPP = 5V
20
30
40
50
60
70
80
90
100
0 10203040
POSITIVE LOW-POWER CHARGE-PUMP
EFFICIENCY vs. LOAD CURRENT
MAX1747 toc11
IPOS (mA)
EFFICIENCY (%)
VSUPP = 6V
VSUPP = 5V
VPOS = 12V
VSUPP = 7V
MAX1747
Triple Charge-Pump TFT LCD
DC-DC Converter
_______________________________________________________________________________________ 7
4
10
22
16
28
34
37591113
MAXIMUM POSITIVE CHARGE-PUMP
OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
MAX1747 toc13
VSUPP (V)
VPOS (V)
IPOS = 1mA
IPOS = 10mA
VPOS(NOMINAL) = 32V
LOAD TRANSIENT
MAX1747 toc14
40µs/div
200mA
100mA
0
5.05V
4.95V
5V
VIN = 3.3V, VOUT = 5.0V
ROUT = 500Ω TO 25Ω
CINTG = 1500pF
IOUT
100mA/div
VOUT
50mV/div
RIPPLE WAVEFORM
MAX1747 toc15
400ns/div
VOUT = +5.0V,IOUT = 200mA
VNEG = -7V, INEG = 10mA
VPOS = +12V, IPOS = 5mA
VOUT
20mV/div
VNEG
10mV/div
VPOS
10mV/div
STARTUP WAVEFORM (NO LOAD)
MAX1747 toc16
1ms/div
2V
2V
0
4V
4V
0
2V
VON
2V/div
VCXP
2V/div
VOUT
2V/div
VOUT = 5V, NO LOAD
ON CONNECTED TO SHDN THROUGH
A 58kΩ RESISTOR
STARTUP WAVEFORM (200mA LOAD)
MAX1747 toc17
1ms/div
2V
2V
0
4V
4V
0
2V
VOUT = 5V, ROUT = 25Ω (200mA)
VON
2V/div
VCXP
2V/div
VOUT
2V/div
ON CONNECTED TO SHDN THROUGH
A 58kΩ RESISTOR
POWER-UP SEQUENCE
MAX1747 toc18
ON CONNECTED TO SHDN THROUGH
A 58kΩ RESISTOR
2V
0
0
5V
-10V
0
10V
2ms/div
VMAIN = 5V, VNEG = -7V, VPOS = 12V
VON
2V/div
VMAIN
5V/div
VPOS
10V/div
VNEG
10V/div
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = VSUPM = +3.3V, TA= +25°C, unless otherwise noted.)
MAX1747
Triple Charge-Pump TFT LCD
DC-DC Converter
8 _______________________________________________________________________________________
Detailed Description
The MAX1747 is an efficient triple-output power supply
for TFT LCD applications. The device contains one
high-power charge pump and two low-power charge
pumps. The MAX1747 charge pumps switch continu-
ously at a constant frequency, so the output noise con-
tains well-defined frequency components, and the
circuit requires much smaller external capacitors for a
given output ripple. The adjustable switching frequency
is set by the current into the shutdown pin (see
Frequency Selection and Shutdown).
The main charge pump uses internal MOSFETs with
low RON to provide high output current. The adjustable
output voltage of the main charge pump can be set up
to 5.5V with external resistors. The dual low-power
charge pumps independently regulate a positive output
PIN NAME FUNCTION
1, 2 TGND Must be connected to ground.
3RDY Active-Low Open-Drain Output. Indicates all outputs are ready. The RON is 125Ω (typ).
4FB
Main Charge-Pump Feedback Input. Regulates to 1.25V nominal. Connect to the center of a
feedback resistive divider between the main output (OUT) and analog ground (GND).
5 INTG Main Charge-Pump Integrator Output. If used, connect 1500pF to analog ground (GND). To disable
the integrator, connect to GND.
6IN
Supply Input. +2.7V to +4.5V input range. Powers only the logic and reference. Bypass to analog
ground (GND) with a 0.1µF capacitor as close to the pin as possible.
7 GND Analog Ground. Connect to power ground (PGND) underneath the IC.
8 REF Internal Reference Bypass Terminal. Connect a 0.22µF capacitor from this terminal to analog
ground (GND). External load capability to 50µA. REF is disabled in shutdown.
9 FBP Positive Charge-Pump Feedback Input. Regulates to 1.25V nominal. Connect feedback resistive
divider to analog ground (GND).
10 FBN Negative Charge-Pump Regulator Feedback Input. Regulates to 0V nominal. Connect feedback
resistive divider to the reference (REF).
11 SHDN
Shutdown Input. Drive SHDN through an external resistor. When SHDN is pulled low, the device
turns off and draws only 0.1µA. OUT is also pulled low through an internal 10Ω resistor in shutdown
mode. When current is sourced into SHDN through RFREQ, the device activates, and the SHDN
input current sets the oscillator’s switching frequency:
RFREQ (kΩ) = 45.5 (MHz / mA) ✕ (VON - 0.7V) / fOSC (MHz)
12 DRVN Negative Charge-Pump Driver Output. Output high level is VSUPN, and low level is PGND.
13 SUPN Negative Charge-Pump Driver Supply Voltage. Bypass to power ground (PGND) with a 0.1µF
capacitor.
14 DRVP Positive Charge-Pump Driver Output. Output high level is VSUPP and low level is PGND.
15 SUPP Positive Charge-Pump Driver Supply Voltage. Bypass to power ground (PGND) with a 0.1µF
capacitor.
16 PGND Power Ground. Connect to analog ground (GND) underneath the IC.
17 CXN Negative Terminal of the Main Charge-Pump Flying Capacitor
18 SUPM Main Charge-Pump Supply Voltage Input
19 CXP Positive Terminal of the Main Charge-Pump Flying Capacitor
20 OUT
Main Charge-Pump Output. Bypass to power ground (PGND) with 10µF for a 1MHz application
(see Output Capacitor Selection). An internal 10Ω resistor discharges the output when the device
is shut down.
Pin Description
MAX1747
Triple Charge-Pump TFT LCD
DC-DC Converter
_______________________________________________________________________________________ 9
(VPOS) and a negative output (VNEG). These two out-
puts use external diode and capacitor stages (as many
stages as required) to regulate output voltages above
+35V and under -35V.
A proprietary regulation algorithm minimizes output rip-
ple as well as capacitor sizes for all three charge
pumps. Also included in the MAX1747 are a precision
1.25V reference that sources up to 50µA, shutdown,
power-up sequencing, fault detection, and an active-
low open-drain ready output.
Main Charge Pump
During the first half-cycle, the MAX1747 charges the
flying capacitor (CX) by connecting it between the sup-
ply voltage (VSUPM) and ground (Figure 2). This initial
charge is controlled by the variable N-channel on-resis-
tance. During the second half-cycle, the MAX1747 level
shifts the flying capacitor by stacking the voltage
across CX on top of the supply voltage. This transfers
the sum of the two voltages to the output capacitor
(COUT).
Dual Charge-Pump Regulators
The MAX1747 contains two individual low-power
charge pumps. Using a single stage, the first charge
pump inverts the supply voltage (VSUPN) and provides
a regulated negative output voltage. The second
charge pump doubles the supply voltage (VSUPP) and
provides a regulated positive output voltage. The
MAX1747 contains internal P-channel and N-channel
MOSFETs to control the power transfer. The internal
MOSFETs switch at a constant frequency set by the
current into the shutdown pin (see Frequency Selection
and Shutdown).
VOUT
+5V, 200mA
VIN = 3.0V
D6
D5
D8
CIN
10µFR7
100k RFREQ
100k
C1
0.1µF
C5
0.1µF
D3
D4
C6
1.0µF
C9
0.1µF
D7
VNEG
-7V, 10mA C10
1.0µF
R5
280k
R6
49.9k
CREF
0.22µF
CX
0.47µF
C11
0.1µF
C12
0.1µF
COUT
(2) 4.7µFR1
150k
R2
49.9k
D1
D2
C7
0.1µF
C3
0.1µF
C4
1.0µF
VPOS
+12V, 5mA
C8
1.0µF
R3
432k
R4
49.9k
CINTG
1500pF
SUPM
IN
RDY
SHDN
DRVN
FBN
REF
TGND
GND
CXP
CXN
OUT
SUPP
SUPN
FB
DRVP
FBP
INTG
PGND
MAX1747
Figure 1. Typical Application Circuit
MAX1747
Triple Charge-Pump TFT LCD
DC-DC Converter
10 ______________________________________________________________________________________
Negative Charge Pump
During the first half-cycle, the P-channel MOSFET turns
on, and flying capacitor C5 charges to VSUPN minus a
diode drop (Figure 3). During the second half-cycle,
the P-channel MOSFET turns off, and the N-channel
MOSFET turns on, level shifting C5. This connects C5 in
parallel with the reservoir capacitor, C6. If the voltage
across C6 minus a diode drop is lower than the voltage
across C5, current flows from C5 to C6 until the diode
(D4) turns off. The amount of charge transferred to the
output is controlled by the variable N-channel RON.
Positive Charge Pump
During the first half-cycle, the N-channel MOSFET turns
on and charges the flying capacitor, C3 (Figure 4). This
initial charge is controlled by the variable N-channel
RON. During the second half-cycle, the N-channel
MOSFET turns off, and the P-channel MOSFET turns
on, level shifting C3 by VSUPP volts. This connects C3
in parallel with the reservoir capacitor, C4. If the voltage
across C4 plus a diode drop (VPOS + VDIODE) is small-
er than the level-shifted flying capacitor voltage (VC3 +
VSUPP), charge flows from C3 to C4 until the diode (D2)
turns off.
Frequency Selection and Shutdown
The shutdown pin (SHDN) on the MAX1747 performs a
dual function: it shuts down the device and determines
the oscillator frequency. The SHDN input looks like a
diode to ground and should be driven through a resis-
tor (Figure 5).
Driving SHDN low forces all three MAX1747 converters
into shutdown mode. When disabled, the supply cur-
rent drops to 20µA (max) to maximize battery life, and
OUT is pulled to ground through an internal 10Ωresis-
tor. For the low-power charge pumps, the output
capacitance and load current determine the rate at
which each output voltage will decay. The device acti-
vates (see Power-up Sequencing) once SHDN is for-
ward biased (minimum of 3µA of current). Do not leave
SHDN floating. For a typical application where shut-
down is used only to set the switching frequency, con-
nect SHDN to the input (VIN = 3.3V) with a 120kΩ
resistor for a 1MHz switching frequency.
The bias current into SHDN, programmed with an exter-
nal resistor, determines the oscillator frequency (see
Typical Operating Characteristics). To select the fre-
quency, calculate the external resistor value, RFREQ,
using the following formula:
RFREQ = 45.5 (MHz / mA) ✕(VON – 0.7V) / fOSC
where RFREQ is in kΩand fOSC is in MHz. Program the
frequency in the 200kHz to 2MHz range. This frequen-
cy range corresponds to SHDN input currents between
3µA to 65µA. Proper operation of the oscillator is not
guaranteed beyond these limits. Forcing SHDN below
400mV disables the device.
Soft-Start
For the MAX1747, soft-start is achieved by controlling
the rise rate of the output voltage, regardless of output
capacitance or output load, and limited only by the out-
put impedance of the regulator (see Startup Waveforms
SUPM
C1
VSUPM = VIN
2.7V TO 4.5V
R1
CX
R2
VOUT = [1+ (R1/R2)] ✕ VREF
VREF = 1.25V
GND
VREF
1.25V
PGND
INTG
CINTG
REF
FB
CXN
CXP
OUT
OSC
MAX1747 VOUT
COUT
CREF
gm
Figure 2. Main Charge-Pump Block Diagram
MAX1747
OSC
VREF
1.25V
GND PGND
SUPN
DRVN
FBN
REF
R6
CREF
VNEG = -(R5/R6) ✕ VREF
VREF = 1.25V
C6
VNEG
R5
D3
C5
D4
VSUPP = 2.7V TO 13V
Figure 3. Negative Charge-Pump Block Diagram
MAX1747
Triple Charge-Pump TFT LCD
DC-DC Converter
______________________________________________________________________________________ 11
in the Typical Operating Characteristics). The main out-
put voltage is controlled to be in regulation within 4096
clock cycles (1/fOSC). The negative and positive low-
power charge pumps are controlled to be in regulation
within 2048 clock cycles.
Power-Up Sequencing
Upon power-up or exiting shutdown, the MAX1747
starts a power-up sequence. First, the reference pow-
ers up. Then the primary charge pump powers up with
soft-start enabled. Once the main charge pump reach-
es 90% of its nominal value (VFB > 1.125V), the nega-
tive charge pump turns on. When the negative output
voltage reaches approximately 90% of its nominal value
(VFBN < 125mV), the positive charge pump starts up.
Finally, when the positive output voltage reaches 90%
of its nominal value (VFBP > 1.125V), the active-low
ready signal (RDY) goes low (see Power Ready).
Fault Detection
Once RDY is low, and if any output falls below its fault
detection threshold, RDY goes high impedance.
For the reference, the fault threshold is 1.05V. For the
main charge pump, the fault threshold is 88% of its
nominal value (VFB < 1.1V). For the negative charge
pump, the fault threshold is approximately 88% of its
nominal value (VFBN > 140mV). For the positive charge
pump, the fault threshold is 88% of its nominal value
(VFBP < 1.1V).
Once an output faults, all outputs later in the power
sequence shut down until the faulted output rises
above its power-up threshold. For example, if the nega-
tive charge-pump output voltage falls below the fault-
detection threshold, the main charge pump remains
active while the positive charge pump stops switching
and its output voltage decays, depending on output
capacitance and load. The positive charge-pump out-
put will not power up until the negative charge-pump
output voltage rises above its power-up threshold (see
Power-Up Sequencing).
Power Ready
Power ready is an open-drain output. When the power-
up sequence is properly completed, the MOSFET turns
on and pulls RDY low with a typical 125ΩRON. If a fault
is detected, the internal open-drain MOSFET appears
as a high impedance. Connect a 100kΩpullup resistor
between RDY and IN for a logic level output.
Voltage Reference
The voltage at REF is nominally 1.25V. The reference
can source up to 50mA with excellent load regulation
(see Typical Operating Characteristics). Connect a
0.22µF bypass capacitor between REF and GND.
During shutdown, the reference is disabled.
Design Procedure
Efficiency Considerations
The efficiency characteristics of the MAX1747 regulat-
ed charge pumps are similar to a linear regulator. They
are dominated by quiescent current at low output cur-
rents and by the input voltage at higher output currents
(see Typical Operating Characteristics). Therefore, the
maximum efficiency may be approximated by:
Efficiency ≅VOUT / (2 ✕VSUPM) for the main
charge pump
Efficiency ≅- VNEG / (VSUPN ✕N) for the negative
low-power charge pump
OSC
SUPP
DRVP
FBP
PGND
VREF
1.25V
MAX1747
GND
C3 D1
D2
R3
R4 C4
VPOS
VPOS = [1 + (R3/R4)] ✕ VREF
VREF = 1.25V
VSUPP = 2.7V TO 13V
Figure 4. Positive Charge-Pump Block Diagram
MAX1747 IN
SHDN
GND
RFREQ
VON = VIN
CIN
RFREQ = kFREQ ✕ (VON - 0.7V)/fOSC
RFREQ IS IN kΩ, kFREQ IS 45.5MHz/mA,
AND fOSC IS IN MHz.
OSC
Figure 5. Frequency Adjustment
MAX1747
Triple Charge-Pump TFT LCD
DC-DC Converter
12 ______________________________________________________________________________________
Efficiency ≅VPOS / [VSUPP ✕(N+1)] for the
positive low-power charge pump
where N is the number of charge-pump stages.
Output Voltage Selection
Adjust the main output voltage by connecting a volt-
age-divider from the output (VOUT) to FB and GND (see
Typical Operating Circuit). Adjust the negative low-
power output voltage by connecting a voltage-divider
from the output (VNEG) to FBN to REF. Adjust the posi-
tive low-power output voltage by connecting a voltage-
divider from the output (VPOS) to FBP to GND. Select
R2, R4, and R6 in the 10kΩto 200kΩrange. Calculate
the remaining resistors with the following equations:
R1 = R2 [(VOUT / VREF) – 1]
R3 = R4 [(VPOS / VREF) – 1]
R5 = R6 |VNEG / VREF|
where VREF = 1.25V. VOUT may range from 4.5V to
5.5V, VPOS may range from VSUPP to +35V, and VNEG
may range from 0 to -35V.
Flying Capacitors
Increasing the flying capacitor’s value increases the
output-current capability. Above a certain point, larger
capacitor values lower the secondary pole formed by
the transfer capacitor and switch RON, which destabi-
lizes the output. For the main charge pump, use a
ceramic capacitor based on the following equation:
For the low-power charge pumps, a 0.1µF ceramic
capacitor works well in most applications. Smaller val-
ues may be used for lower current applications.
Component suppliers are listed in Table 1.
Output Capacitors
For the main charge pump, use a ceramic capacitor
based on the following equation:
For low-frequency applications (close to 200kHz),
selection of the output capacitor is limited solely by the
switching frequency. However, for high-frequency
applications (close to 2MHz), selection of the output
capacitor is limited by the secondary pole formed by
the flying capacitor and switch on-resistance.
For the low-power charge pumps, the output capacitor
should be anywhere from 5-times to 20-times larger
than the flying capacitor, depending on the ripple toler-
ance. Increasing the output capacitance or decreasing
the ESR reduces the output ripple voltage and the
peak-to-peak transient voltage.
Input Capacitors
Using an input capacitor with a value equal to or
greater than the output capacitor is recommended.
Place the capacitor as close to the IC as possible. If the
source impedance or inductance of the input supply is
large, additional input bypassing may be required.
For the low-power charge-pump inputs (SUPN and
SUPP), using bypass capacitors with values equal to or
greater than the flying capacitors is recommended.
Place these capacitors as close to the supply voltage
inputs as possible.
Rectifier Diodes
Use Schottky diodes with a current rating greater than
4 times the average output current, and with a voltage
rating of 1.5 times VSUPP for the positive charge pump
and VSUPN for the negative charge pump.
Integrator Capacitor
The MAX1747 contains an internal current integrator
that improves the DC load regulation but increases the
peak-to-peak transient voltage (see Load-Transient
Waveform in the Typical Operating Characteristics).
Connect a ceramic capacitor between INTG and GND
based on the following equation:
CHz C
f
INTG OUT
OSC
≥×150
CMCM
OUT X
≥××
×
20 2
Hz f AND FHz
f
OSC OSC
µ
CF MHz
f
XOSC
≤µ×047.
SUPPLIER PHONE FAX
CAPACITORS
AVX 803-946-0690 803-626-3123
Kemet 408-986-0424 408-986-1442
Sanyo 619-661-6835 619-661-1055
Taiyo Yuden 408-573-4150 408-573-4159
DIODES
Central 516-435-1110 516-435-1824
International
Rectifier 310-322-3331 310-322-3332
Motorola 602-303-5454 602-994-6430
Nihon 847-843-7500 847-843-2798
Table 1. Component Suppliers
MAX1747
Triple Charge-Pump TFT LCD DC-DC Converter
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13
© 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information
PC Board Layout and Grounding
Careful printed circuit layout is important to minimize
ground bounce and noise. First, place the main charge-
pump flying capacitor less than 0.2in (5mm) from the
CXP and CXN pins with wide traces and no vias. Then
place 0.1µF ceramic bypass capacitors near the
charge-pump input pins (SUPP and SUPN) to the
PGND pin. Keep the charge-pump circuitry as close to
the IC as possible, using wide traces and avoiding vias
when possible. Locate all feedback resistive dividers as
close to their respective feedback pins as possible. The
PC board should feature separate analog and power
ground areas connected at only one point under the IC.
To maximize output power and efficiency, and minimize
output power ripple voltage, use extra-wide power
ground traces, and solder the IC’s power ground pin
directly to it. Avoid having sensitive traces near the
switching nodes and high-current lines.
Refer to the MAX1747 evaluation kit for an example of
proper board layout.
Chip Information
TRANSISTOR COUNT: 2534
TSSOP,NO PADS.EPS
