MAX8795AGCJ/V+T Maxim Integrated Products, MAX8795AGCJ/V+T Datasheet

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MAX8795AGCJ/V+T

Manufacturer Part Number
MAX8795AGCJ/V+T
Description
Display Drivers TFT-LCD DC-DC Conver ter with Operational
Manufacturer
Maxim Integrated Products
Datasheet
1.MAX8795AETJ.pdf (31 pages)

Specifications of MAX8795AGCJ/V+T

Lead Free Status / RoHS Status
Lead free / RoHS Compliant
The MAX8795A includes a high-performance step-up
regulator, two linear-regulator controllers, and five high-
current operational amplifiers for active-matrix, thin-film
transistor (TFT), liquid-crystal displays (LCDs). Also
included is a logic-controlled, high-voltage switch with
adjustable delay.
The step-up DC-DC converter provides the regulated
supply voltage for the panel source driver ICs. The con-
verter is a high-frequency (1.2MHz) current-mode regu-
lator with an integrated 20V n-channel MOSFET that
allows the use of ultra-small inductors and ceramic
capacitors. It provides fast transient response to pulsed
loads while achieving efficiencies over 85%.
The gate-on and gate-off linear-regulator controllers
provide regulated TFT gate-on and gate-off supplies
using external charge pumps attached to the switching
node. The MAX8795A includes five high-performance
operational amplifiers. These amplifiers are designed to
drive the LCD backplane (VCOM) and/or the gamma-
correction divider string. The device features high out-
put current (±130mA), fast slew rate (45V/µs), wide
bandwidth (20MHz), and rail-to-rail inputs and outputs.
The MAX8795A is available in a lead-free, 32-pin, thin
QFN package with a maximum thickness of 0.8mm for
ultra-thin LCD panels, as well as in a 32-pin LQFP
package with 0.8mm pin pitch.
19-0793; Rev 3; 3/11
+ Denotes a lead(Pb)-free/RoHS-compliant package.
/V Denotes an automotive-qualified part.
Pin Configurations appear at end of data sheet.
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
MAX8795AETJ+
MAX8795AGCJ+
MAX8795AGTJ+
MAX8795AGTJ/V+
Notebook Computer Displays
LCD Monitor Panels
Automotive Displays
PART
________________________________________________________________ Maxim Integrated Products
-40°C to +105°C
-40°C to +105°C
-40°C to +85°C
-40°C to +85°C
TEMP RANGE
Ordering Information
General Description
Applications
PIN-PACKAGE
32 Thi n QFN
32 LQ FP
32 TQ FN
32 TQ FN
TFT-LCD DC-DC Converter with
o 2.5V to 5.5V Input Supply Range
o 1.2MHz Current-Mode Step-Up Regulator
o Linear-Regulator Controllers for V
o High-Performance Operational Amplifiers
o Logic-Controlled, High-Voltage Switch with
o Timer-Delay Fault Latch for All Regulator Outputs
o Thermal-Overload Protection
o 0.6mA Quiescent Current
Operational Amplifiers
Adjustable Delay
Fast Transient Response to Pulsed Load
High-Accuracy Output Voltage (1%)
Built-In 20V, 3A, 0.16Ω n-Channel MOSFET
High Efficiency (85%)
±130mA Output Short-Circuit Current
45V/µs Slew Rate
20MHz, -3dB Bandwidth
Rail-to-Rail Inputs/Outputs
V
IN
Minimal Operating Circuit
IN
COMP
SRC
COM
DRN
SUP
NEG1
OUT1
POS1
NEG2
OUT2
POS2
OUT3
POS3
OP1
OP2
V
OP3
CN
CONTROLLER
CONTROLLER
GATE-ON
STEP-UP
CONTROL
MAX8795A
SWITCH
CONTROLLER
GATE-OFF
EP
BGND
REF
OP4
OP5
LX
PGND
AGND
DRVP
DRVN
NEG4
OUT4
POS4
NEG5
OUT5
POS5
FBP
DEL
CTL
FBN
REF
FB
GON
V
CP
Features
V
MAIN
and V
V
V
V
V
CP
GON
CN
GOFF
GOFF
1

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MAX8795AGCJ/V+T Summary of contents

Page 1

... Denotes a lead(Pb)-free/RoHS-compliant package. /V Denotes an automotive-qualified part. Pin Configurations appear at end of data sheet. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. TFT-LCD DC-DC Converter with Operational Amplifiers o 2 ...

Page 2

TFT-LCD DC-DC Converter with Operational Amplifiers ABSOLUTE MAXIMUM RATINGS IN, CTL to AGND ...................................................-0.3V to +7.5V COMP, FB, FBP, FBN, DEL, REF to AGND ....-0. PGND, BGND to AGND ......................................................±0. PGND ............................................................-0.3V to +20V SUP to ...

Page 3

ELECTRICAL CHARACTERISTICS (continued 3V 14V, V PGND IN MAIN SUP unless otherwise noted.) PARAMETER SYMBOL FB Transconductance FB Voltage Gain LX On-Resistance R LX Leakage Current LX Current Limit Current-Sense Transresistance Soft-Start Period Soft-Start ...

Page 4

TFT-LCD DC-DC Converter with Operational Amplifiers ELECTRICAL CHARACTERISTICS (continued 3V 14V, V PGND IN MAIN SUP unless otherwise noted.) PARAMETER SYMBOL GATE-OFF LINEAR-REGULATOR CONTROLLER FBN Regulation Voltage FBN Fault Trip Level FBN Input Bias ...

Page 5

ELECTRICAL CHARACTERISTICS ( 14V, V PGND IN MAIN SUP PARAMETER SYMBOL IN Supply Range IN Undervoltage-Lockout V Threshold IN Quiescent Current REF Output Voltage REF Undervoltage-Lockout Threshold MAIN STEP-UP REGULATOR Output Voltage Range V ...

Page 6

TFT-LCD DC-DC Converter with Operational Amplifiers ELECTRICAL CHARACTERISTICS (continued 3V 14V, V PGND IN MAIN SUP PARAMETER SYMBOL GATE-OFF LINEAR-REGULATOR CONTROLLER FBN Regulation Voltage FBN Effective Load-Regulation Error (Transconductance) FBN Line (IN) Regulation Error ...

Page 7

ELECTRICAL CHARACTERISTICS (continued 3V 14V, V PGND IN MAIN SUP unless otherwise noted.) PARAMETER SYMBOL MAIN STEP-UP REGULATOR Output Voltage Range V Operating Frequency Oscillator Maximum Duty Cycle FB Regulation Voltage FB Fault Trip ...

Page 8

TFT-LCD DC-DC Converter with Operational Amplifiers ELECTRICAL CHARACTERISTICS (continued 3V 14V, V PGND IN MAIN SUP unless otherwise noted.) PARAMETER SYMBOL GATE-ON LINEAR-REGULATOR CONTROLLER FBP Regulation Voltage FBP Fault Trip Level FBP Input Bias ...

Page 9

ELECTRICAL CHARACTERISTICS ( 14V, V PGND IN MAIN SUP PARAMETER SYMBOL IN Supply Range IN Undervoltage-Lockout V Threshold IN Quiescent Current REF Output Voltage REF Undervoltage-Lockout Threshold MAIN STEP-UP REGULATOR Output Voltage Range V ...

Page 10

TFT-LCD DC-DC Converter with Operational Amplifiers ELECTRICAL CHARACTERISTICS (continued 3V 14V, V PGND IN MAIN SUP PARAMETER SYMBOL GATE-ON LINEAR-REGULATOR CONTROLLER FBP Regulation Voltage V FBP Effective Load-Regulation Error (Transconductance) FBP Line (IN) Regulation ...

Page 11

Figure 5V 14V MAIN STEP-UP EFFICIENCY vs. LOAD CURRENT 13.9V MAIN 100 1000 LOAD CURRENT (mA) STEP-UP REGULATOR ...

Page 12

TFT-LCD DC-DC Converter with Operational Amplifiers (Circuit of Figure 5V 14V MAIN GATE-OFF REGULATOR LINE REGULATION 0.4 0.2 0 -0.2 -0.4 -0.6 -0 50mA NEG -1.0 -16 -14 -12 -10 INPUT ...

Page 13

Figure 5V 14V MAIN OPERATIONAL-AMPLIFIER LOAD-TRANSIENT RESPONSE MAX8795A toc15 A 0V +50mA B 0mA -50mA 400ns/div A: OUTPUT VOLTAGE, 1V/div, AC-COUPLED B: OUTPUT CURRENT, 50mA/div PIN NAME Switch Input. Source of ...

Page 14

TFT-LCD DC-DC Converter with Operational Amplifiers PIN NAME 17 OUT4 Operational-Amplifier 4 Output 18 POS5 Operational-Amplifier 5 Noninverting Input 19 NEG5 Operational-Amplifier 5 Inverting Input 20 OUT5 Operational-Amplifier 5 Output n-Channel Power MOSFET Drain and Switching Node. Connect the inductor ...

Page 15

Typical Operating Circuit The MAX8795A typical operating circuit (Figure complete power-supply system for TFT LCDs. The circuit generates a +14V source-driver supply and +25V and V IN 4.5V TO 5.5V C1 22μF 180kΩ LX C12 C11 220μF ...

Page 16

TFT-LCD DC-DC Converter with Operational Amplifiers Table 2. Component Suppliers SUPPLIER PHONE Fairchild 408-822-2000 Sumida 847-545-6700 TDK 847-803-6100 Toshiba 949-455-2000 STEP-UP CONTROLLER PGND COMP AGND MAX8795A DRVP GATE-ON CONTROLLER SRC COM SWITCH CONTROL DRN ...

Page 17

RESET DOMINANT CLOCK ILIM COMPARATOR SOFT- START SLOPE COMP PWM Σ COMPARATOR OSCILLATOR FAULT COMPARATOR TO FAULT LATCH ERROR AMP 1.14V Figure 3. Step-Up Regulator Functional Diagram voltage, the controller resets the flip-flop and turns off the ...

Page 18

TFT-LCD DC-DC Converter with Operational Amplifiers REG P is enabled after the REF voltage exceeds 1.0V. Each time it is enabled, the controller goes through a soft-start routine that ramps up its internal reference DAC in 128 steps. Gate-Off Linear-Regulator ...

Page 19

INPUT SOFT- SOFT- SWITCH VOLTAGE START START CONTROL OK BEGINS ENDS ENABLED Figure 6. Power-Up Sequence IN 5μA DEL REF CTL Figure 7. Switch-Control Block ______________________________________________________________________________________ TFT-LCD DC-DC Converter with Operational Amplifiers C . Once the ...

Page 20

TFT-LCD DC-DC Converter with Operational Amplifiers 30Ω p-channel switch (Q2) between DRN and COM turns off. If CTL is low, Q1 turns off and Q2 turns on. During steady-state operation, if the output of the main regulator or any of ...

Page 21

Choosing an LIR of 0.5 and estimating efficiency of 85% at this operating point: ⎛ ⎞ 2 ⎛ − ⎞ ⎛ ⎜ ⎟ ⎜ ⎟ ⎜ L ...

Page 22

TFT-LCD DC-DC Converter with Operational Amplifiers The number of positive charge-pump stages is given by GON DROPOUT = n POS − × MAIN where n is the number of positive charge-pump POS stages ...

Page 23

Charge-Pump Output Capacitor Increasing the output capacitance or decreasing the ESR reduces the output ripple voltage and the peak-to- peak transient voltage. With ceramic capacitors, the output voltage ripple is dominated by the capacitance value. Use the following equation to ...

Page 24

TFT-LCD DC-DC Converter with Operational Amplifiers and gate-off linear-regulator controllers are 0.1mA. Therefore, the base-to-emitter resistor for both linear regulators should be chosen to set 0.1mA bias current ...

Page 25

The largest portions of power dissipation in the step-up regulator are the internal MOSFET, the inductor, and the output diode. If the step-up regulator has 90% efficiency, approximately the power is lost in the internal MOSFET, ...

Page 26

TFT-LCD DC-DC Converter with Operational Amplifiers TOP VIEW DRVP DRVN TOP VIEW DRVP DRVN 26 ______________________________________________________________________________________ FBP 25 26 FBN 27 28 MAX8795A DEL 29 CTL 30 DRN 31 COM ...

Page 27

For the latest package outline information and land patterns (footprints www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing per- ...

Page 28

TFT-LCD DC-DC Converter with Operational Amplifiers For the latest package outline information and land patterns (footprints www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different ...

Page 29

For the latest package outline information and land patterns (footprints www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing per- ...

Page 30

TFT-LCD DC-DC Converter with Operational Amplifiers For the latest package outline information and land patterns (footprints www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different ...

Page 31

... 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 ____________________ 31 © 2010 Maxim Integrated Products ...

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