Rainbow Electronics MAX1747 User Manual

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 highpower and two low-power charge pumps convert the +2.7V to +4.5V input supply voltage into three independent output voltages.

The primary high-power charge pump generates an output voltage (V

OUT

) 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 switching frequency (200kHz to 2MHz) provides fast transient response and allows the use of small low-profile ceramic capacitors.

The dual low-power charge pumps independently regulate one positive output (V

POS

) and one negative output

NEG

). 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 capacitor 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

Pin Configuration

19-1788; Rev 0; 10/00

Ordering Information

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)

Typical Operating Circuit

EVALUATION KIT

AVAILABLE

TOP VIEW

TGND

RDY

INTG

GND

FBP

OUT

CXP

SUPM

CXNFB

MAX1747

PGND

SUPP

DRVP

SUPNREF

DRVN

SHDNFBN

PART TEMP. RANGE PIN-PACKAGE

MAX1747EUP -40°C to +85°C 20 TSSOP

INPUT

TO µC

NEGATIVE

OUTPUT

MAX1747

CXP

CXN

OUT

SUPP

SUPN

DRVP

FBP

INTG

PGND

MAIN OUTPUT

POSITIVE OUTPUT

SUPM

SHDN RDY

DRVN

FBN

REF

TGND GND

TSSOP

MAX1747

Triple Charge-Pump TFT LCD DC-DC Converter

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VIN= V

SUPM

= +3.0V, V

SUPP

= V

SUPN

= +5V, TGND = PGND = GND, I

SHDN

= 22µA, C

OUT

= 2 ✕4.7µF, C

REF

= 0.22µF, C

INTG

1500pF, V

OUT

= +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 (V

SUPM

+ 0.3V)

CXP to PGND ............................(V

SUPM

- 0.3V) to (V

OUT

+ 0.3V)

DRVN to GND .........................................-0.3V to (V

SUPN

+ 0.3V)

DRVP to GND..........................................-0.3V to (V

SUPP

+ 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 (V

+ 0.3V)

Continuous Current into:

SUPM, CXN, CXP, OUT ..............................................±800mA

SUPP, SUPN, DRVN, DRVP........................................±200mA

SHDN...........................................................................+100µA

All Other Pins ....................................................................±10mA

Continuous Power Dissipation (T

= +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

)

Input Supply Range V

Input Undervoltage Threshold V

Input Quiescent Supply Current

PARAMETER SYMBOL CONDITIONS MIN TYP MAX U N IT S

UVLO

IIN +

SUPM

VIN falling, 40mV hysteresis (typ) 2.2 2.4 2.6 V

VFB = V

FBP

no load on DRVN and DRVP; CXN and CXP open

= 1.5V, V

2.7 4.5 V

= -0.2V, V

FBN

OUT

= 5V,

0.9 1.0 mA

Output Quiescent Supply Current

Q(OUT

Shutdown Supply Current V

Operating Frequency f

OSC

VFB = V no load on DRVN and DRVP; CXN and CXP open

SHDN

= 1.5V, V

FBP

= -0.2V, V

FBN

OUT

= 5V,

2.5 4.0 mA

= 0, V

= 5V 0.1 20 µA

SUPM

= 22µA 0.65 1 1.2 MHz

MAIN CHARGE PUMP

Output Voltage Range V

Maximum Output Current I

OU T( M AX ) CX

FB Regulation Voltage V

FB Input Bias Current I

OUT

= 0.47µF 200 mA

VFB = 1.25V -50 +50 nA

4.5 5.5 V

1.237 1.248 1.263 V

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

/ F

OSC

NEGATIVE LOW-POWER CHARGE PUMP

SUPN Input Supply Range V

SUPN Quiescent Current I

SUPN

SUPN Shutdown Current V

FBN Regulation Voltage V

FBN

= -0.2V, no load on DRVN 0.6 0.8 mA

FBN

SHDN

= 0, V

= 13V 0.1 10 µA

SUPN

2.7 13 V

-50 0 +50 mV

MAX1747

Triple Charge-Pump TFT LCD

DC-DC Converter

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VIN= V

SUPM

= +3.0V, V

SUPP

= V

SUPN

= +5V, TGND = PGND = GND, I

SHDN

= 22µA, C

OUT

= 2 ✕4.7µF, C

REF

= 0.22µF, C

INTG

1500pF, V

OUT

= +5V, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

FBN Input Bias Current I DRVN PCH On-Resistance 36Ω

DRVN NCH On-Resistance

FBN Power-Ready Trip Level Falling edge 80 125 165 mV

FBN Fault Trip Level Rising edge 140 mV

Negative Soft-Start Period

POSITIVE LOW-POWER CHARGE PUMP

SUPP Input Supply Range V

SUPP Quiescent Current I

SUPP Shutdown Current V

FBP Regulation Voltage V

FBP Input Bias Current I DRVP PCH On-Resistance 36Ω

DRVP NCH On-Resistance

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

REFERENCE

Reference Voltage V

Reference Undervoltage Threshold

LOGIC SIGNALS

SHDN Input Low Voltage 0.4 V SHDN Bias Voltage I SHDN Bias Voltage Tempco 2 mV/°C SHDN Input Current Range I RDY Output Low Voltage I RDY Output High Leakage V

PARAMETER SYMBOL CONDITIONS MIN TYP MAX U N IT S

FBN

SUPP

FBP

REF

SHDN

= -50mV -50 +50 nA

FBN

= 50mV 1 5 Ω

FBN

= -50mV 20 kΩ

FBN

= 1.5V, no load on DRVP 0.6 0.8 mA

FBP

= 0, V

SHDN

= 1.5V -50 +50 nA

FBP

= 1.20V 1.5 5 Ω

FBP

= 1.30V 20 kΩ

FBP

-2µA < I

For 200kHz to 2MHz operation 3 65 µA

REF

rising 0.95 1.05 1.18 V

REF

= 22µA 580 724 830 mV

SHDN

= 2mA 0.25 0.5 V

SINK

= 13V 0.01 1 µA

RDY

= 13V 0.1 10 µA

SUPP

< 50µA 1.231 1.25 1.269 V

2.7 13 V

1.20 1.25 1.30 V

2.048/ F

OSC

2.048/ F

OSC

MAX1747

Triple Charge-Pump TFT LCD DC-DC Converter

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS

= V

SUPM

= +3.0V, V

SUPP

= V

SUPN

= +5V, TGND = PGND = GND, I

SHDN

= 22µA, C

OUT

= 2 ✕4.7µF, C

REF

= 0.22µF, C

INTG

1500pF, V

OUT

= +5V, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)

Input Supply Range V

Input Undervoltage Threshold V

Input Quiescent Supply Current

PARAMETER SYMBOL CONDITIONS MIN MAX UNITS

UVLO

IIN +

SUPM

VIN falling, 40mV hysteresis (typ) 2.2 2.6 V

VFB = V

FBP

no load on DRVN and DRVP; CXN and CXP open

= 1.5V, V

FBN

= -0.2V, V

OUT

= 5V,

2.7 4.5 V

1.0 mA

Output Quiescent Supply Current

Q(OUT)

Input Shutdown Current V

Operating Frequency f

OSC

VFB = V no load on DRVN and DRVP; CXN and CXP open

SHDN

= 1.5V, V

FBP

= -0.2V, V

FBN

OUT

= 5V,

4.0 mA

= 0, V

= 5V 20 µA

SUPM

= 22µA 0.65 1.2 MHz

MAIN CHARGE PUMP

Output Voltage Range V

Output Current I

OU T ( M AX ) CX

FB Regulation Voltage V

FB Input Bias Current I

OUT

= 0.47µF 200 mA

VFB = 1.25V -50 +50 nA

4.5 5.5 V

1.222 1.271 V

FB Power-Ready Trip Level Rising edge 1.09 1.16 V

NEGATIVE LOW-POWER CHARGE PUMP

SUPN Input Supply Range V

SUPN Quiescent Current I

SUPN

SUPN Shutdown Current V

FBN Regulation Voltage V

FBN Input Bias Current I

FBN

= -0.2V, no load on DRVN 0.8 mA

FBN

= 0, V

SHDN

= 0 -50 +50 nA

FBN

= 13V 10 µA

SUPN

2.7 13 V

-50 +50 mV

DRVN PCH On-Resistance 6 Ω

= 50mV 5 Ω

DRVN NCH On-Resistance

FBN

= -50mV 20 kΩ

FBN

FBN Power-Ready Trip Level Falling edge 80 165 mV

POSITIVE LOW-POWER CHARGE PUMP

SUPP Input Supply Range V

SUPP Quiescent Current I

SUPP

SUPP Shutdown Current V

FBP Regulation Voltage V

FBP Input Bias Current I

FBP

= 1.5V, no load on DRVP 0.8 mA

FBP

= 0, V

SHDN

= 1.5V -50 +50 nA

FBP

= 13V 10 µA

SUPP

2.7 13 V

1.20 1.30 V

DRVP PCH On-Resistance 6 Ω

= 1.20V 5 Ω

DRVP NCH On-Resistance

FBP

= 1.30V 20 kΩ

FBP

FBP Power-Ready Trip Level Rising edge 1.09 1.16 V

MAX1747

Triple Charge-Pump TFT LCD

DC-DC Converter

_______________________________________________________________________________________ 5

ELECTRICAL CHARACTERISTICS (continued)

= V

SUPM

= +3.0V, V

SUPP

= V

SUPM

= +5V, TGND = PGND = GND, I

SHDN

= 22µA, C

OUT

= 2 ✕4.7µF, C

REF

= 0.22µF, C

INTG

1500pF, V

OUT

= +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= V

SUPM

= +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

OUT

(mA)

OUT

(V)

MAIN OUTPUT EFFICIENCY

vs. LOAD CURRENT

(MAIN CHARGE PUMP ONLY)

VIN = 3.3V

VIN = 4.0V

VIN = 2.8V

100

0200100 300 400

MAX1747 toc02

OUT

(mA)

EFFICIENCY (%)

MAIN OUTPUT EFFICIENCY

vs. LOAD CURRENT

(MAIN CHARGE PUMP ONLY)

OUT

= 5V

VIN = 3.3V

VIN = 4.0V

VIN = 2.8V

100

0200100 300 400

MAX1747 toc03

OUT

(mA)

EFFICIENCY (%)

MAIN OUTPUT EFFICIENCY

vs. LOAD CURRENT

(MAIN CHARGE PUMP ONLY)

OUT

= 5V

VIN = 3.3V

VIN = 4.0V

VIN = 2.8V

NEG

= -7V WITH I

NEG

= 10mA

POS

= 12V WITH I

POS

= 5mA

PARAMETER SYMBOL CONDITIONS MIN MAX UNITS

REFERENCE

Reference Voltage V

Reference Undervoltage Threshold

REF

-2µA < I

REF

< 50µA 1.222 1.269 V

REF

rising 0.95 1.18 V

LOGIC SIGNALS

Input Low Voltage 0.4 V

SHDN

Bias Voltage I

SHDN

Input Current Range I

SHDN

Output Low Voltage I

RDY

Output High Leakage V

RDY

SHDN

= 22µA 580 900 mV

SHDN

For 200kHz to 2MHz operation 3 65 µA

= 2mA 0.5 V

SINK

= 13V 1 µA

RDY

MAX1747

Triple Charge-Pump TFT LCD DC-DC Converter

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(Circuit of Figure 1, VIN= V

SUPM

= +3.3V, TA= +25°C, unless otherwise noted.)

0 0.5 1.0 1.5 2.0

NO-LOAD SUPPLY CURRENT vs. SWITCHING FREQUENCY

MAX1747 toc04

FREQUENCY (MHz)

+ I

(mA)

0.4

1.2

0.8

1.6

2.0

02010 30 40 50

SWITCHING FREQUENCY

vs. I

SHDN

MAX1747 toc05

SHDN

(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)

+ I

SUPM

(mA)

NO-LOAD SUPPLY CURRENT

vs. TEMPERATURE

VON = 3.3V

FREQ

= 120k

Ω

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

FREQ

= 120k

Ω

100

0 10203040

NEGATIVE LOW-POWER CHARGE-PUMP

EFFICIENCY vs. LOAD CURRENT

MAX1747 toc08

NEG

(mA)

EFFICIENCY (%)

SUPN

= 6V

SUPN

= 5V

SUPN

= 7V

NEG

= -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

NEG

(mA)

NEG

(V)

SUPN

= 5V

SUPN

= 6V

SUPN

= 7V

-22

-18

-10

-14

-6

-2

37591113

MAXIMUM NEGATIVE CHARGE-PUMP

OUTPUT VOLTAGE vs. SUPPLY VOLTAGE

MAX1747 toc10

SUPN

(V)

NEG

(V)

NEG

= 10mA

NEG

= 1mA

NEG(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

POS

(mA)

POS

(V)

SUPP

= 7V

SUPP

= 6V

SUPP

= 5V

100

0 10203040

POSITIVE LOW-POWER CHARGE-PUMP

EFFICIENCY vs. LOAD CURRENT

MAX1747 toc11

POS

(mA)

EFFICIENCY (%)

SUPP

= 6V

SUPP

= 5V

POS

= 12V

SUPP

= 7V

MAX1747

Triple Charge-Pump TFT LCD

DC-DC Converter

_______________________________________________________________________________________ 7

Typical Operating Characteristics (continued)

(Circuit of Figure 1, VIN= V

SUPM

= +3.3V, TA= +25°C, unless otherwise noted.)

MAXIMUM POSITIVE CHARGE-PUMP

OUTPUT VOLTAGE vs. SUPPLY VOLTAGE

POS(NOMINAL)

(V)

POS

37591113

RIPPLE WAVEFORM

= 32V

MAX1747 toc15

MAX1747 toc13

OUT

20mV/div

NEG

10mV/div

POS

10mV/div

= 1mA

POS

= 10mA

POS

(V)

SUPP

200mA

100mA

5.05V

4.95V

LOAD TRANSIENT

40µs/div

= 3.3V, V

OUT

INTG

= 5.0V

OUT

= 500Ω TO 25

= 1500pF

Ω

STARTUP WAVEFORM (NO LOAD)

MAX1747 toc14

MAX1747 toc16

OUT

100mA/div

OUT

50mV/div

2V/div

CXP

2V/div

OUT

2V/div

OUT

NEG

POS

= +5.0V,I = -7V, I = +12V, I

NEG

OUT

= 10mA

POS

= 200mA

= 5mA

STARTUP WAVEFORM (200mA LOAD)

400ns/div

= 5V, R

OUT

ON CONNECTED TO SHDN THROUGH A 58kΩ RESISTOR

1ms/div

= 25Ω (200mA)

OUT

MAX1747 toc17

2V/div

CXP

2V/div

OUT

2V/div

= 5V, NO LOAD

OUT

ON CONNECTED TO SHDN THROUGH A 58kΩ RESISTOR

-10V

10V

= 5V, V

MAIN

ON CONNECTED TO SHDN THROUGH A 58kΩ RESISTOR

1ms/div

POWER-UP SEQUENCE

2ms/div

NEG

= -7V, V

POS

= 12V

MAX1747 toc18

2V/div

MAIN

5V/div

NEG

10V/div

POS

10V/div

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 continuously at a constant frequency, so the output noise contains 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 R

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 Description

PIN NAME FUNCTION

1, 2 TGND Must be connected to ground.

3 RDY Active-Low Open-Drain Output. Indicates all outputs are ready. The RON is 125Ω (typ).

4FB

5 INTG

6IN

7 GND Analog Ground. Connect to power ground (PGND) underneath the IC.

8 REF

9 FBP

10 FBN

11 SHDN

12 DRVN Negative Charge-Pump Driver Output. Output high level is V

13 SUPN

14 DRVP Positive Charge-Pump Driver Output. Output high level is V

15 SUPP

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 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).

Main Charge-Pump Integrator Output. If used, connect 1500pF to analog ground (GND). To disable the integrator, connect to GND.

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.

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.

Positive Charge-Pump Feedback Input. Regulates to 1.25V nominal. Connect feedback resistive divider to analog ground (GND).

Negative Charge-Pump Regulator Feedback Input. Regulates to 0V nominal. Connect feedback resistive divider to the reference (REF).

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 R input current sets the oscillator’s switching frequency:

(kΩ) = 45.5 (MHz / mA)

FREQ

Negative Charge-Pump Driver Supply Voltage. Bypass to power ground (PGND) with a 0.1µF capacitor.

Positive Charge-Pump Driver Supply Voltage. Bypass to power ground (PGND) with a 0.1µF capacitor.

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.

, the device activates, and the SHDN

FREQ

(VON - 0.7V) / f

SUPN

and low level is PGND.

SUPP

(MHz)

OSC

, and low level is PGND.

MAX1747

Triple Charge-Pump TFT LCD

DC-DC Converter

_______________________________________________________________________________________ 9

POS

) and a negative output (V

NEG

). These two outputs 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 ripple 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 activelow open-drain ready output.

Main Charge Pump

During the first half-cycle, the MAX1747 charges the flying capacitor (CX) by connecting it between the supply voltage (V

SUPM

) and ground (Figure 2). This initial charge is controlled by the variable N-channel on-resistance. 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 (C

OUT

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 (V

SUPN

) and provides a regulated negative output voltage. The second charge pump doubles the supply voltage (V

SUPP

) 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).

Figure 1. Typical Application Circuit

= 3.0V

10µF

1.0µF

NEG

-7V, 10mA

100k

C10

1.0µF

SUPM

0.1µF

REF

0.1µF

49.9k

FREQ

100k

280k

0.22µF

RDY

SHDN

DRVN

MAX1747

FBN

REF

TGND

GND

CXP

CXN

OUT

SUPP

SUPN

DRVP

FBP

INTG

PGND

C11

0.1µF

0.47µF

C12

0.1µF

INTG

1500pF

OUT

+5V, 200mA

OUT

(2) 4.7µF

49.9k

432k

R1 150k

49.9k

1.0µF

POS

+12V, 5mA

1.0µF

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 V

SUPN

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 V

SUPP

volts. This connects C3 in parallel with the reservoir capacitor, C4. If the voltage across C4 plus a diode drop (V

POS

+ V

DIODE

) is smaller than the level-shifted flying capacitor voltage (VC3+ V

SUPP

), 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 resistor (Figure 5).

Driving SHDN low forces all three MAX1747 converters into shutdown mode. When disabled, the supply current drops to 20µA (max) to maximize battery life, and OUT is pulled to ground through an internal 10Ω resistor. For the low-power charge pumps, the output capacitance and load current determine the rate at which each output voltage will decay. The device activates (see Power-up Sequencing) once SHDN is forward biased (minimum of 3µA of current). Do not leave SHDN floating. For a typical application where shutdown is used only to set the switching frequency, connect SHDN to the input (V

= 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 frequency, calculate the external resistor value, R

FREQ

using the following formula:

FREQ

= 45.5 (MHz / mA) ✕(VON– 0.7V) / f

OSC

where R

FREQ

is in kΩ and f

OSC

is in MHz. Program the

frequency in the 200kHz to 2MHz range. This frequency 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 output impedance of the regulator (see Startup Waveforms

Figure 2. Main Charge-Pump Block Diagram

Figure 3. Negative Charge-Pump Block Diagram

= V

SUPM

2.7V TO 4.5V

MAX1747

OUT

OSC

MAX1747

SUPM

OSC

OUT

CXP

SUPN

DRVN

= 2.7V TO 13V

SUPP

INTG

PGND

REF

1.25V

CXN

REF

GND

= [1+ (R1/R2)] ✕ V

OUT

= 1.25V

REF

NEG

REF

V V

= -(R5/R6) ✕ V

NEG

= 1.25V

REF

FBN

REF

1.25V

REF

GND PGND

MAX1747

Triple Charge-Pump TFT LCD

DC-DC Converter

______________________________________________________________________________________ 11

in the Typical Operating Characteristics). The main output voltage is controlled to be in regulation within 4096 clock cycles (1/f

OSC

). The negative and positive lowpower 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 powers up. Then the primary charge pump powers up with soft-start enabled. Once the main charge pump reaches 90% of its nominal value (VFB> 1.125V), the negative charge pump turns on. When the negative output voltage reaches approximately 90% of its nominal value (V

FBN

< 125mV), the positive charge pump starts up. Finally, when the positive output voltage reaches 90% of its nominal value (V

FBP

> 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 (V

FBN

> 140mV). For the positive charge pump, the fault threshold is 88% of its nominal value (V

FBP

< 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 negative charge-pump output voltage falls below the faultdetection 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 output 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 powerup sequence is properly completed, the MOSFET turns on and pulls RDY low with a typical 125Ω R

. If a fault

is detected, the internal open-drain MOSFET appears as a high impedance. Connect a 100kΩ pullup 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 regulated charge pumps are similar to a linear regulator. They are dominated by quiescent current at low output currents and by the input voltage at higher output currents (see Typical Operating Characteristics). Therefore, the maximum efficiency may be approximated by:

Efficiency ≅ V

OUT

/ (2 ✕V

SUPM

) for the main

charge pump Efficiency ≅ - V

NEG

/ (V

SUPN

N) for the negative

low-power charge pump

MAX1747

Figure 4. Positive Charge-Pump Block Diagram

Figure 5. Frequency Adjustment

OSC

SUPP

DRVP

VON = V

= 2.7V TO 13V

SUPP

MAX1747

OSC

SHDN

FREQ

FBP

REF

1.25V

GND

PGND

= [1 + (R3/R4)] ✕ V

POS

= 1.25V

REF

POS

REF

GND

= k

FREQ

IS IN kΩ, k

IS IN MHz.

OSC

(VON - 0.7V)/f

IS 45.5MHz/mA,

FREQ

OSC

R R AND f

FREQ FREQ

MAX1747

Triple Charge-Pump TFT LCD DC-DC Converter

12 ______________________________________________________________________________________

Efficiency ≅ V

POS

/ [V

SUPP

(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 voltage-divider from the output (V

OUT

) to FB and GND (see Typical Operating Circuit). Adjust the negative lowpower output voltage by connecting a voltage-divider from the output (V

NEG

) to FBN to REF. Adjust the positive low-power output voltage by connecting a voltagedivider from the output (V

POS

) to FBP to GND. Select

R2, R4, and R6 in the 10kΩ to 200kΩ range. Calculate the remaining resistors with the following equations:

R1 = R2 [(V

OUT

/ V

REF

) – 1]

R3 = R4 [(V

POS

/ V

REF

) – 1]

R5 = R6 |V

NEG

/ V

REF

where V

REF

= 1.25V. V

OUT

may range from 4.5V to

5.5V, V

POS

may range from V

SUPP

to +35V, and V

NEG

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 destabilizes 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 values 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 tolerance. 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 V

SUPP

for the positive charge pump

and V

SUPN

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:

Table 1. Component Suppliers

≤

F MHz

µ×047.

OSC



20 2



≥××



OUT X

 







f AND



OSC





FHz





OSC

 



  



INTG

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

International Rectifier

Motorola 602-303-5454 602-994-6430

Nihon 847-843-7500 847-843-2798

Hz C

×150

≥

516-435-1110 516-435-1824

310-322-3331 310-322-3332

OSC

OUT

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

Package Information

PC Board Layout and Grounding

Careful printed circuit layout is important to minimize ground bounce and noise. First, place the main chargepump 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

Rainbow Electronics MAX1747 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual