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MAX8795AETJ+-MAX8795AETJ+T-MAX8795AGCJ/V+T
TFT-LCD DC-DC Converter with Operational Amplifiers
General DescriptionThe 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 MAX8795Aincludes 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 MAX8795Ais 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.
ApplicationsNotebook Computer Displays
LCD Monitor Panels
Automotive Displays
Features2.5V to 5.5V Input Supply Range1.2MHz Current-Mode Step-Up Regulator
Fast Transient Response to Pulsed Load
High-Accuracy Output Voltage (1%)
Built-In 20V, 3A, 0.16Ωn-Channel MOSFET
High Efficiency (85%)Linear-Regulator Controllers for VGONand VGOFFHigh-Performance Operational Amplifiers
±130mA Output Short-Circuit Current
45V/µs Slew Rate
20MHz, -3dB Bandwidth
Rail-to-Rail Inputs/OutputsLogic-Controlled, High-Voltage Switch with
Adjustable DelayTimer-Delay Fault Latch for All Regulator OutputsThermal-Overload Protection0.6mA Quiescent Current
TFT-LCD DC-DC Converter with
Operational Amplifiers
Ordering InformationSTEP-UP
CONTROLLER
GATE-ON
CONTROLLER
SWITCH
CONTROL
GATE-OFF
CONTROLLER
REF
VCNVCP
VMAIN
PGND
AGND
DRVP
FBP
VCP
VGON
VCN
VGOFF
DEL
CTL
DRVN
FBN
NEG4
REF
POS4
NEG5
POS5
OUT4
OUT5
BGND
NEG2
POS2
OP3
POS3
OUT2
OUT3
POS1
OUT1
NEG1
SUP
COM
DRN
SRC
COMP
VIN
MAX8795A
OP2
OP1
OP5
OP4
Minimal Operating Circuit19-0793; Rev 5; 5/12
PARTTEMP RANGEPIN-PACKAGEMAX8795AETJ+-40°C to +85°C32 Thi n QFN
MAX8795AGCJ+-40°C to +105°C32 LQ FP
MAX8795AGCJ/V+-40°C to +105°C32 LQ FP
MAX8795AGTJ+-40°C to +105°C32 TQ FN
MAX8795AGTJ/V+-40°C to +105°C32 TQ FN
+Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive-qualified part.
EVALUATION KIT
AVAILABLE
MAX8795A
TFT-LCD DC-DC Converter with
Operational Amplifiers
ABSOLUTE MAXIMUM RATINGSStresses 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, CTL to AGND...................................................-0.3V to +7.5V
COMP, FB, FBP, FBN, DEL, REF to AGND....-0.3V to (VIN+ 0.3V)
PGND, BGND to AGND......................................................±0.3V
LX to PGND............................................................-0.3V to +20V
SUP to AGND.........................................................-0.3V to +20V
DRVP to AGND.......................................................-0.3V to +36V
POS_, NEG_, OUT_ to AGND...................-0.3V to (VSUP+ 0.3V)
DRVN to AGND...................................(VIN- 30V) to (VIN+ 0.3V)
SRC to AGND.........................................................-0.3V to +40V
COM, DRN to AGND................................-0.3V to (VSRC+ 0.3V)
DRN to COM............................................................-30V to +30V
POS_ to NEG_ RMS Current...................................5mA(Note 1)
OUT_ Maximum Continuous Output Current....................±75mA
LX Switch Maximum Continuous RMS Current.....................1.6A
Continuous Power Dissipation (TA= +70°C)
32-Pin Thin QFN (derate 34.5mW/°C above +70°C)2758mW
32-Pin LQFP (derate 48.4mW/°C above +70°C)....1652.9mW
Operating Temperature Range, E Grade............-40°C to +85°C
Operating Temperature Range, G Grade.........-40°C to +105°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
Soldering Temperature (reflow).......................................+260°C
ELECTRICAL CHARACTERISTICS(VIN= 3V, VMAIN= VSUP= 14V, VPGND= VAGND= VBGND= 0V, IREF= 25µA, TA
= 0°C to +85°C. Typical values are at TA= +25°C,
unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSIN Supply RangeVIN(Note 2)2.56.0V
IN Undervoltage-Lockout
ThresholdVUVLOVIN rising, typical hysteresis = 50mV2.052.252.45V
VFB = VFBP = 1.3V, VFBN = 0V,
LX not switching0.61.0
IN Quiescent CurrentIIN
VFB = 1.2V, VFBP = 1.4V, VFBN = 0V,
LX switching23
Duration-to-Trigger Fault
Condition
FB or FBP below threshold or FBN above
threshold200ms
TA = +25°C to +85°C1.2381.2501.262REF Output VoltageNo external loadTA = 0°C to +85°C1.2321.2501.266V
REF Load Regulation0 < ILOAD < 50µA10mV
REF Sink CurrentIn regulation10µA
REF Undervoltage Lockout
ThresholdRising edge; typical hysteresis = 160mV1.15V
Temperature rising+160Thermal ShutdownHysteresis15°C
MAIN STEP-UP REGULATOROutput Voltage RangeVMAINVIN18V
Operating FrequencyfOSC100012001400kHz
Oscillator Maximum Duty Cycle869093%
TA = +25°C to +85°C1.2211.2331.245FB Regulation VoltageVFBNo loadTA = 0°C to +85°C1.2121.2331.248V
FB Fault Trip LevelVFB falling1.101.141.17V
FB Load Regulation0 < IMAIN < full load, transient only-1%
FB Line RegulationVIN = 2.5V to 6V0.1±0.4%/ V
Note 1:See Figure 2 for the op amp clamp structure.
TFT-LCD DC-DC Converter with
Operational Amplifiers
ELECTRICAL CHARACTERISTICS (continued)(VIN= 3V, VMAIN= VSUP= 14V, VPGND= VAGND= VBGND= 0V, IREF= 25µA, TA
= 0°C to +85°C. Typical values are at TA= +25°C,
unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSFB Transconductance∆ICOMP = ±2.5µA75160280µS
FB Voltage GainFrom FB to COMP700V/ V
LX On-ResistanceRLX(ON)ILX = 200mA160260mΩ
LX Leakage CurrentILXVLX = 19V1020µA
LX Current LimitILIMVFB = 1.2V, duty cycle = 75%2.53.03.5A
Current-Sense Transresistance0.10.20.3V/A
Soft-Start PeriodtSS14ms
Soft-Start Step SizeVREF /
128V
OPERATIONAL AMPLIFIERSSUP Supply RangeVSUP6.018.0VU P O ver vol tag e Faul t Thr eshol d 18.01919.9V
SUP Supply CurrentISUPBuffer configuration, VPOS_ = VSUP / 2,
no load3.55.0mA
Input Offset VoltageVOS(VNEG_, VPOS_, VOUT_) ≅ VSUP / 2012mV
Input Bias CurrentIBIAS(VNEG_ , VPOS_, VOUT_) ≅ VSUP / 2-500+50nA
Input Common-Mode Voltage
RangeVCM0VSUPV
Common-Mode Rejection RatioCMRR0 ≤ (VNEG_, VPOS_) ≤ VSUP4580dB
Open-Loop Gain125dB
Output Voltage Swing, HighVOHIOUT_ = 5mAVSUP -
VSUP -mV
Output Voltage Swing, LowVOLIOUT_ = -5mA50100mV
Short-Circuit CurrentTo VSUP / 2, source or sink75130mA
Power-Supply Rejection RatioPSRRDC, 6V ≤ VSUP ≤ 18V,
(VNEG_, VPOS_) ≅ VSUP / 260dB
Slew Rate45V/µs
-3dB BandwidthRL = 10kΩ, CL = 10pF, buffer configuration20MHz
GATE-ON LINEAR-REGULATOR CONTROLLERFBP Regulation VoltageVFBPIDRVN = 100µA 1.231 1.250 1.269 VFBP Fault Trip LevelVFBP falling 0.96 1.00 1.04 VFBP Input Bias CurrentIFBPVFBP = 1.25V -50 +50 nAFBP Effective Load-Regulation
Error (Transconductance)VDRVP = 10V, IDRVP = 50µA to 1mA -0.7 -1.5 %FBP Line (IN) Regulation ErrorIDRVP = 100µA, 2.5V < VIN < 6V ±1 ±10 mVDRVP Sink CurrentIDRVPVFBP = 1.1V, VDRVP = 10V 1 5 mADRVP Off-Leakage CurrentVFBP = 1.4V, VDRVP = 34V 0.01 10 µASoft-Start PeriodtSS 14 msVREF /
MAX8795A
TFT-LCD DC-DC Converter with
Operational Amplifiers
ELECTRICAL CHARACTERISTICS (continued)(VIN= 3V, VMAIN= VSUP= 14V, VPGND= VAGND= VBGND= 0V, IREF= 25µA, TA
= 0°C to +85°C. Typical values are at TA= +25°C,
unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
GATE-OFF LINEAR-REGULATOR CONTROLLERFBN Regulation VoltageVFBN IDRVN = 100µA, VREF - VFBN 0.984 1 1.015 VFBN Fault Trip Level VFBN rising 370 420 470 mVFBN Input Bias CurrentIFBN VFBN = 0.25V -50 +50 nAFBN Effective Load-Regulation
Error (Transconductance) VDRVN = -10V, IDRVN = 50µA to 1mA 11 25 mVFBN Line (IN) Regulation Error IDRVN = 0.1mA, 2.5V < VIN < 6V ±0.7 ±5 mVDRVN Source CurrentIDRVN VFBN = 300mV, VDRVN = -10V 1 5 mADRVN Off-Leakage Current VFBN = 0V, VDRVN = -25V -0.01 -10 µASoft-Start PeriodtSS 14 msSoft-Start Step Size (VREF -
VFBN) /
128 V
POSITIVE GATE-DRIVER TIMING AND CONTROL SWITCHESDEL Capacitor Charge CurrentDuring startup, VDEL = 1V456µA
DEL Turn-On ThresholdVTH(DEL)1.191.251.31V
DEL Discharge Switch
On-ResistanceDuring UVLO, VIN = 2.0V20Ω
CTL Input Low VoltageVIN = 2.5V to 5.5V0.6V
CTL Input High VoltageVIN = 2.5V to 5.5V2V
CTL Input Leakage CurrentCTL = AGND or IN-1+1µA
CTL-to-SRC Propagation Delay100ns
SRC Input Voltage Range36V
VDEL = 1.5V, CTL = IN200300SRC Input CurrentISRCVDEL = 1.5V, CTL = AGND115200µARC - to- C O M S w i tch On- Resi stanceRSRC(ON)VDEL = 1.5V, CTL = IN510ΩRN - to- C O M S w i tch
On- Resi stanceRDRN(ON)VDEL = 1.5V, CTL = AGND3060Ω
TFT-LCD DC-DC Converter with
Operational Amplifiers
PARAMETERSYMBOLCONDITIONSMINMAXUNITSIN Supply RangeVIN(Note 2)2.56.0V
IN Undervoltage-Lockout
ThresholdVUVLOVIN rising, typical hysteresis = 150mV2.052.45V
VFB = VFBP = 1.3V, VFBN = 0V,
LX not switching1.0
IN Quiescent CurrentIIN
VFB = 1.2V, VFBP = 1.4V, VFBN = 0V,
LX switching3
REF Output VoltageNo external load1.2181.277V
REF Undervoltage-Lockout
ThresholdRising edge; typical hysteresis = 160mV1.15V
MAIN STEP-UP REGULATOROutput Voltage RangeVMAINVIN18V
Operating FrequencyfOSC9001400kHz
FB Regulation VoltageVFBNo load1.1981.260V
FB Line RegulationVIN = 2.5V to 6V±0.4%/ V
FB Transconductance∆ICOMP = ±2.5µA75280µS
LX On-ResistanceRLX(ON)ILX = 200mA260mΩ
LX Current LimitILIMVFB = 1.2V, duty cycle = 75%2.53.5A
OPERATIONAL AMPLIFIERSSUP Supply RangeVSUP618V
SUP Overvoltage Fault Threshold18.019.9V
SUP Supply CurrentISUPBuffer configuration, VPOS_ = VSUP / 2,
no load5mA
Input Offset VoltageVOS(VNEG_, VPOS_, IOUT_) = ≅ VSUP / 212mV
Input Common-Mode Voltage
RangeVCM0VSUPV
Output Voltage Swing, HighVOHIOUT_ = 5mAVSUP -
100mV
Output Voltage Swing LowVOLIOUT_ = -5mA100
Source75Short-Circuit CurrentTo VSUP / 2Sink75mA
GATE-ON LINEAR-REGULATOR CONTROLLERFBP Regulation VoltageVFBPIDRVP = 100µA 1.210 1.280 VFBP Effective Load-Regulation
Error (Transconductance)VDRVP = 10V, IDRVP = 50µA to 1mA -1.5 %FBP Line (IN) Regulation ErrorIDRVP = 100µA, 2.5V < VIN < 6V 10 mVDRVP Sink CurrentIDRVPVFBP = 1.1V, VDRVP = 10V 1 mA
ELECTRICAL CHARACTERISTICS(VIN= 3V, VMAIN= VSUP= 14V, VPGND= VAGND= VBGND= 0V, IREF= 25µA, TA
= -40°C to +85°C,unless otherwise noted.) (Note 3)
MAX8795A
TFT-LCD DC-DC Converter with
Operational Amplifiers
ELECTRICAL CHARACTERISTICS (continued)(VIN= 3V, VMAIN= VSUP= 14V, VPGND= VAGND= VBGND= 0V, IREF= 25µA, TA
= -40°C to +85°C,unless otherwise noted.) (Note 3)
PARAMETERSYMBOLCONDITIONSMINMAXUNITS
GATE-OFF LINEAR-REGULATOR CONTROLLERFBN Regulation VoltageVFBN IDRVN = 100µA, VREF - VFBN 0.972 1.022 VFBN Effective Load-Regulation
Error (Transconductance) VDRVN = -10V, IDRVN = 50µA to 1mA 25 mVFBN Line (IN) Regulation Error IDRVN = 0.1mA, 2.5V < VIN < 6V ±5 mVDRVN Source CurrentIDRVN VFBN = 300mV, VDRVN = -10V 1 mA
POSITIVE GATE-DRIVER TIMING AND CONTROL SWITCHESDEL Capacitor Charge CurrentDuring startup, VDEL = 1V46µA
DEL Turn-On ThresholdVTH(DEL)1.191.31V
CTL Input Low VoltageVIN = 2.5V to 5.5V0.6V
CTL Input High VoltageVIN = 2.5V to 5.5V2V
SRC Input Voltage Range36V
VDEL = 1.5V, CTL = IN300SRC Input CurrentISRCVDEL = 1.5V, CTL = AGND200µARC - to- C O M S w i tch On- Resi stanceRSRC(ON)VDEL = 1.5V, CTL = IN10ΩRN - to- C O M S w i tch On- Resi stanceRDRN(ON)VDEL = 1.5V, CTL = AGND60Ω
ELECTRICAL CHARACTERISTICS(VIN= 3V, VMAIN= VSUP= 14V, VPGND= VAGND= VBGND= 0V, IREF= 25µA, TA
= 0°C to +105°C. Typical values are at TA= +25°C,
unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSIN Supply RangeVIN(Note 2)2.56.0V
IN Undervoltage-Lockout
ThresholdVUVLOVIN rising, typical hysteresis = 50mV2.052.252.45V
VFB = VFBP = 1.3V, VFBN = 0V,
LX not switching0.61.0
IN Quiescent CurrentIIN
VFB = 1.2V, VFBP = 1.4V, VFBN = 0V,
LX switching23
Duration-to-Trigger Fault
Condition
VFB or FBP below threshold or FBN above
threshold200ms
TA = +25°C to +105°C1.2381.2501.262REF Output VoltageNo external loadTA = 0°C to +105°C1.2321.2501.266V
REF Load Regulation0 < ILOAD < 50µA10mV
REF Sink CurrentIn regulation10µA
REF Undervoltage-Lockout
ThresholdRising edge, typical hysteresis = 160mV1.15V
Temperature rising+160
TFT-LCD DC-DC Converter with
Operational Amplifiers
ELECTRICAL CHARACTERISTICS (continued)(VIN= 3V, VMAIN= VSUP= 14V, VPGND= VAGND= VBGND= 0V, IREF= 25µA, TA
= 0°C to +105°C. Typical values are at TA= +25°C,
unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
MAIN STEP-UP REGULATOROutput Voltage RangeVMAINVIN18V
Operating FrequencyfOSC100012001400kHz
Oscillator Maximum Duty Cycle869093%
TA = +25°C to +105°C1.2211.2331.245FB Regulation VoltageVFBNo loadTA = 0°C to +105°C1.2121.2331.248V
FB Fault Trip LevelVFB falling1.101.141.17V
FB Load Regulation0 < IMAIN < full load, transient only-1
FB Line RegulationVIN = 2.5V to 6V0.1±0.4%/V
FB Input Bias CurrentVFB = 1.233V+100+200nA
FB Transconductance∆ICOMP = ±2.5µA75160280µS
FB Voltage GainFrom FB to COMP700V/V
LX On-ResistanceRLX(ON)ILX = 200mA160300mΩ
LX Leakage CurrentILXVLX = 19V1020µA
LX Current LimitILIMVFB = 1.2V, duty cycle = 75%2.53.03.5A
Current-Sense Transresistance0.10.20.3V/A
Soft-Start PeriodtSS14ms
Soft-Start Step SizeVREF /
128V
OPERATIONAL AMPLIFIERSSUP Supply RangeVSUP6.018.0
SUP Overvoltage Fault Threshold18.01919.9V
SUP Supply CurrentISUPBuffer configuration, VPOS_ = VSUP / 2,
no load3.55.0mA
Input Offset VoltageVOS(VNEG_, VPOS_, VOUT_) ≅ VSUP / 2012mV
Input Bias CurrentIBIAS(VNEG_, VPOS_, VOUT_) ≅ VSUP / 2-500+50nA
Input Common-Mode Voltage
RangeVCM0VSUPV
Common-Mode Rejection RatioCMRR0 ≤ (VNEG_, VPOS_) ≤ VSUP4580dB
Open-Loop Gain125dB
Output Voltage Swing, HighVOHIOUT_ = 5mAVSUP -
VSUP -mV
Output Voltage Swing, LowVOLIOUT_ = -5mA50100mV
Short-Circuit CurrentTo VSUP / 2, source or sink75130mA
Power-Supply Rejection RatioPSRRDC, 6V ≤ VSUP ≤ 18V,
(VNEG_, VPOS_) ≅ VSUP / 260dB
Slew Rate45V/µs
-3dB BandwidthRL = 10kΩ, CL = 10pF, buffer configuration20MHz
MAX8795A
TFT-LCD DC-DC Converter with
Operational Amplifiers
ELECTRICAL CHARACTERISTICS (continued)(VIN= 3V, VMAIN= VSUP= 14V, VPGND= VAGND= VBGND= 0V, IREF= 25µA, TA
= 0°C to +105°C. Typical values are at TA= +25°C,
unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
GATE-ON LINEAR-REGULATOR CONTROLLERFBP Regulation VoltageVFBPIDRVP = 100µA 1.231 1.250 1.269 VFBP Fault Trip LevelVFBP falling 0.96 1.00 1.04 VFBP Input Bias CurrentIFBPVFBP = 1.25V -50 +50 nAFBP Effective Load-Regulation
Error (Transconductance)VDRVP = 10V, IDRVP = 50µA to 1mA -0.7 -1.5 %FBP Line (IN) Regulation ErrorIDRVP = 100µA, 2.5V < VIN < 6V ±1 ±10 mVDRVP Sink CurrentIDRVPVFBP = 1.1V, VDRVP = 10V 1 5 mADRVP Off-Leakage CurrentVFBP = 1.4V, VDRVP = 34V 0.01 10 µASoft-Start PeriodtSS 14 msSoft-Start Step Size VREF /
128 V
GATE-OFF LINEAR-REGULATOR CONTROLLERFBN Regulation VoltageVFBN IDRVN = 100µA, VREF - VFBN 0.984 1 1.015 VFBN Fault Trip Level VFBN rising 340 420 510 mVFBN Input Bias CurrentIFBN VFBN = 0.25V -50 +50 nAFBN Effective Load-Regulation
Error (Transconductance) VDRVN = -10V, IDRVN = 50µA to 1mA 11 25 mVFBN Line (IN) Regulation Error IDRVN = 0.1mA, 2.5V < VIN < 6V ±0.7 ±5 mVDRVN Source CurrentIDRVN VFBN = 300mV, VDRVN = -10V 1 5 mA
DRVN Off-Leakage Current VFBN = 0V, VDRVN = -25V -0.01 -10 µASoft-Start PeriodtSS 14 msSoft-Start Step Size (VREF -
VFBN) /
128 V
POSITIVE GATE-DRIVER TIMING AND CONTROL SWITCHESDEL Capacitor Charge CurrentDuring startup, VDEL = 1V456µA
DEL Turn-On ThresholdVTH(DEL)1.191.251.31V
DEL Discharge Switch
On-ResistanceDuring UVLO, VIN = 2.0V20Ω
CTL Input Low VoltageVIN = 2.5V to 5.5V0.6V
CTL Input High VoltageVIN = 2.5V to 5.5V2V
CTL Input Leakage CurrentCTL = AGND or IN-1+1µA
CTL-to-SRC Propagation Delay100ns
SRC Input Voltage Range36V
VDEL = 1.5V, CTL = IN200300SRC Input CurrentISRCVDEL = 1.5V, CTL = AGND115200µARC - to- C O M S w i tch On- Resi stanceRSRC(ON)VDEL = 1.5V, CTL = IN512Ω
TFT-LCD DC-DC Converter with
Operational Amplifiers
ELECTRICAL CHARACTERISTICS(VIN= 3V, VMAIN= VSUP= 14V, VPGND= VAGND= VBGND= 0V, IREF= 25µA, TA
= -40°C to +105°C, unless otherwise noted.) (Note3)
PARAMETERSYMBOLCONDITIONSMINMAXUNITSIN Supply RangeVIN(Note 2)2.56.0V
IN Undervoltage-Lockout
ThresholdVUVLOVIN rising, typical hysteresis = 150mV2.052.45V
VFB = VFBP = 1.3V, VFBN = 0V,
LX not switching1.0
IN Quiescent CurrentIIN
VFB = 1.2V, VFBP = 1.4V, VFBN = 0V,
LX switching3
REF Output VoltageNo external load1.2181.277V
REF Undervoltage-Lockout
ThresholdRising edge, typical hysteresis = 160mV1.15V
MAIN STEP-UP REGULATOROutput Voltage RangeVMAINVIN18V
Operating FrequencyfOSC9001400kHz
FB Regulation VoltageVFBNo load1.1981.260V
FB Line RegulationVIN = 2.5V to 6V±0.4%/ V
FB Transconductance∆ICOMP = ±2.5µA75280µS
LX On-ResistanceRLX(ON)ILX = 200mA300mΩ
LX Current LimitILIMVFB = 1.2V, duty cycle = 75%2.53.5A
OPERATIONAL AMPLIFIERSSUP Supply RangeVSUP618V
SUP Overvoltage Fault Threshold18.019.9V
SUP Supply CurrentISUPBuffer configuration, VPOS_ = VSUP / 2,
no load5mA
Input Offset VoltageVOS(VNEG_, VPOS_, VOUT_) ≅ VSUP / 212mV
Input Common-Mode Voltage
RangeVCM0VSUPV
Output Voltage Swing, HighVOHIOUT_ = 5mAVSUP -
100mV
Output Voltage Swing, LowVOLIOUT_ = -5mA100mV
Source75Short-Circuit CurrentTo VSUP / 2Sink75mA
MAX8795A
TFT-LCD DC-DC Converter with
Operational Amplifiers
Note 2:For 5.5V < VIN< 6.0V, use MAX8795A for no longer than 1% of IC lifetime. For continuous operation, input voltage should
not exceed 5.5V.
Note 3:Specifications to -40°C and +105°C are guaranteed by design, not production tested.
ELECTRICAL CHARACTERISTICS (continued)(VIN= 3V, VMAIN= VSUP= 14V, VPGND= VAGND= VBGND= 0V, IREF= 25µA, TA
= -40°C to +105°C, unless otherwise noted.) (Note3)
PARAMETERSYMBOLCONDITIONSMINMAXUNITS
GATE-ON LINEAR-REGULATOR CONTROLLERFBP Regulation VoltageVFBPIDRVP = 100µA 1.210 1.280 VFBP Effective Load-Regulation
Error (Transconductance)VDRVP = 10V, IDRVP = 50µA to 1mA -1.5 %FBP Line (IN) Regulation ErrorIDRVP = 100µA, 2.5V < VIN < 6V 10 mVDRVP Sink CurrentIDRVPVFBP = 1.1V, VDRVP = 10V 1 mA
GATE-OFF LINEAR-REGULATOR CONTROLLERFBN Regulation VoltageVFBN IDRVN = 100µA, VREF - VFBN 0.972 1.022 VFBN Effective Load-Regulation
Error (Transconductance) VDRVN = -10V, IDRVN = 50µA to 1mA 25 mVFBN Line (IN) Regulation Error IDRVN = 0.1mA, 2.5V < VIN < 6V ±5 mVDRVN Source CurrentIDRVN VFBN = 300mV, VDRVN = -10V 1 mA
POSITIVE GATE-DRIVER TIMING AND CONTROL SWITCHESDEL Capacitor Charge CurrentDuring startup, VDEL = 1V46µA
DEL Turn-On ThresholdVTH(DEL)1.191.31V
CTL Input Low VoltageVIN = 2.5V to 5.5V0.6V
CTL Input High VoltageVIN = 2.5V to 5.5V2V
SRC Input Voltage Range36V
VDEL = 1.5V, CTL = IN300SRC Input CurrentISRCVDEL = 1.5V, CTL = AGND200µA
SRC-to-COM Switch
On-ResistanceRSRC(ON)VDEL = 1.5V, CTL = IN12Ω
DRN-to-COM Switch
On-ResistanceRDRN(ON)VDEL = 1.5V, CTL = AGND70Ω
TFT-LCD DC-DC Converter with
Operational Amplifiers10μs/div
STEP-UP REGULATOR PULSED
LOAD-TRANSIENT RESPONSE13.9V
50mA
MAX8795A toc05
A: LOAD CURRENT, 1A/div
B: VMAIN, 200mV/div, AC-COUPLED
C: INDUCTOR CURRENT, 1A/div
TIMER-DELAYED OVERLOAD PROTECTIONMAX8795A toc06
40ms/div
A: VMAIN, 2V/div
B: INDUCTOR CURRENT, 1A/div
REF VOLTAGE LOAD REGULATIONMAX8795A toc07
REF VOLTAGE (V)302010
GATE-ON REGULATOR LINE REGULATION
MAX8795A toc08
VOLTAGE ERROR (%)282726
IPOS = 20mA
GATE-ON REGULATOR LOAD REGULATIONMAX8795A toc09
VOLTAGE ERROR (%)105
IBOOST = 200mA
STEP-UP REGULATOR SOFT-START
(HEAVY LOAD)MAX8795A toc04
2ms/div
A: VIN, 5V/div
B: VMAIN, 5V/div
C: INDUCTOR CURRENT, 1A/div
STEP-UP EFFICIENCY
vs. LOAD CURRENTMAX9795A toc01
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = 5V
VMAIN = 13.9V
SWITCHING FREQUENCY
vs. INPUT VOLTAGEMAX9795A toc02
INPUT VOLTAGE (V)
SWITCHING FREQUENCY (MHz)
STEP-UP SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
NO LOAD, SUP DISCONNECTED,
R1 = 221kΩ, R2 = 21.5kΩ
CURRENT INTO INDUCTOR
CURRENT INTO IN PIN
Typical Operating Characteristics(Circuit of Figure 1, VIN= 5V, VMAIN= 14V, VGON= 25V, VGOFF= -10V, TA= +25°C, unless otherwise noted.)
MAX8795A
TFT-LCD DC-DC Converter with
Operational Amplifiers
GATE-OFF REGULATOR LINE REGULATIONMAX8795A toc10
INPUT VOLTAGE (V)
VOLTAGE ERROR (%)
INEG = 50mA
GATE-OFF REGULATOR LOAD REGULATIONMAX8795A toc11
LOAD CURRENT (mA)
VOLTAGE ERROR (%)302010
IBOOST = 0mA
4ms/div
POWER-UP SEQUENCEMAX8795A toc12
A: VMAIN, 10V/div
B: VPOS, 20V/div
C: VNEG, 10V/div
D: VCOM, 20V/div
SUP SUPPLY CURRENT
vs. SUP VOLTAGEISUP
(mA)
MAX8795A toc1381012161418
VSUP (V)4μs/div
OPERATIONAL-AMPLIFIER
RAIL-TO-RAIL INPUT/OUTPUTMAX8795A toc14
A: INPUT SIGNAL, 5V/div
B: OUTPUT SIGNAL, 5V/div
VSUP = 15V
Typical Operating Characteristics (continued)(Circuit of Figure 1, VIN= 5V, VMAIN= 14V, VGON= 25V, VGOFF= -10V, TA= +25°C, unless otherwise noted.)
TFT-LCD DC-DC Converter with
Operational Amplifiers
Typical Operating Characteristics (continued)(Circuit of Figure 1, VIN= 5V, VMAIN= 14V, VGON= 25V, VGOFF= -10V, TA= +25°C, unless otherwise noted.)
400ns/div
OPERATIONAL-AMPLIFIER
LOAD-TRANSIENT RESPONSEMAX8795A toc15
-50mA
A: OUTPUT VOLTAGE, 1V/div, AC-COUPLED
B: OUTPUT CURRENT, 50mA/div
+50mA
0mA
1μs/div
OPERATIONAL-AMPLIFIER
LARGE-SIGNAL RESPONSEMAX8795A toc16
A: INPUT SIGNAL, 5V/div
B: OUTPUT SIGNAL, 5V/div
VSUP = 15V
400ns/div
OPERATIONAL-AMPLIFIER
SMALL-SIGNAL RESPONSEMAX8795A toc17
A: INPUT SIGNAL, 100mV/div
B: OUTPUT SIGNAL, 100mV/div
PINNAMEFUNCTIONSRCSwitch Input. Source of the internal high-voltage p-channel MOSFET. Bypass SRC to PGND with a
minimum 0.1µF capacitor close to the pins.REFReference Bypass Terminal. Bypass REF to AGND with a minimum of 0.22µF close to the pins.AGNDAnalog Ground for Step-Up Regulator and Linear Regulators. Connect to power ground (PGND)
underneath the IC.PGND
Power Ground. PGND is the source of the main step-up n-channel power MOSFET. Connect PGND to
the output-capacitor ground terminals through a short, wide PCB trace. Connect to analog ground
(AGND) underneath the IC.OUT1Operational-Amplifier 1 OutputNEG1Operational-Amplifier 1 Inverting InputPOS1Operational-Amplifier 1 Noninverting InputOUT2Operational-Amplifier 2 OutputNEG2Operational-Amplifier 2 Inverting InputPOS2Operational-Amplifier 2 Noninverting InputBGNDAnalog Ground for Operational Amplifiers. Connect to power ground (PGND) underneath the IC.POS3Operational-Amplifier 3 Noninverting InputOUT3Operational-Amplifier 3 OutputSUPOperational-Amplifier Power Input. Positive supply rail for the operational amplifiers. Typically
connected to VMAIN. Bypass SUP to BGND with a 0.1µF capacitor.POS4Operational-Amplifier 4 Noninverting InputNEG4Operational-Amplifier 4 Inverting Input
Pin Description
MAX8795A
TFT-LCD DC-DC Converter with
Operational Amplifiers
Pin Description (continued)
PINNAMEFUNCTIONOUT4Operational-Amplifier 4 OutputPOS5Operational-Amplifier 5 Noninverting InputNEG5Operational-Amplifier 5 Inverting InputOUT5Operational-Amplifier 5 OutputLXn-Channel Power MOSFET Drain and Switching Node. Connect the inductor and Schottky diode to LX
and minimize the trace area for lowest EMI.INSupply Voltage Input. IN can range from 2.5V to 6V.FBStep-Up Regulator Feedback Input. Regulates to 1.233V (nominal). Connect a resistive voltage-divider
from the output (VMAIN) to FB to analog ground (AGND). Place the divider within 5mm of FB.COMPStep-Up Regulator Error-Amplifier Compensation Point. Connect a series RC from COMP to AGND.
See the Loop Compensation section for component selection guidelines.FBP
Gate-On Linear-Regulator Feedback Input. FBP regulates to 1.25V (nominal). Connect FBP to the
center of a resistive voltage-divider between the regulator output and AGND to set the gate-on linear-
regulator output voltage. Place the resistive voltage-divider within 5mm of FBP.DRVPGate-On Linear-Regulator Base Drive. Open drain of an internal n-channel MOSFET. Connect DRVP to
the base of an external pnp pass transistor. See the Pass-Transistor Selection section.FBN
Gate-Off Linear-Regulator Feedback Input. FBN regulates to 250mV (nominal). Connect FBN to the
center of a resistive voltage-divider between the regulator output and REF to set the gate-off linear-
regulator output voltage. Place the resistive voltage-divider within 5mm of FBN.DRVNGate-Off Linear-Regulator Base Drive. Open drain of an internal p-channel MOSFET. Connect DRVN to
the base of an external npn pass transistor. See the Pass-Transistor Selection section.DELHigh-Voltage Switch Delay Input. Connect a capacitor from DEL to AGND to set the high-voltage
switch startup delay.CTL
High-Voltage Switch Control Input. When CTL is high, the high-voltage switch between COM and SRC
is on and the high-voltage switch between COM and DRN is off. When CTL is low, the high-voltage
switch between COM and SRC is off and the high-voltage switch between COM and DRN is on. CTL is
inhibited by the undervoltage lockout or when the voltage on DEL is less than 1.25V.DRNSwitch Input. Drain of the internal high-voltage back-to-back p-channel MOSFETs connected to COM.COMInternal High-Voltage MOSFET Switch Common Terminal. Do not allow the voltage on COM to exceed
VSRC.EPExposed Paddle. Must be connected to AGND. Do not use as the only ground connection.
TFT-LCD DC-DC Converter with
Operational Amplifiers
Typical Operating CircuitThe MAX8795A typical operating circuit (Figure 1) is a
complete power-supply system for TFT LCDs. The circuit
generates a +14V source-driver supply and +25V and
-10V gate-driver supplies. The input voltage range for the
IC is from +2.5V to +5.5V. The listed load currents in
Figure 1 are available from a +4.5V to +5.5V supply.
Table 1 lists some recommended components, and Table
2 lists the contact information of component suppliers.
0.1μF
0.1μF
C14
68pFC11
0.1μF
3.0μH
22μF
VMAIN
14V/500mA
137kΩ
13.3kΩ
6.8kΩ
1kΩ
R19
100kΩ
R20
100kΩ
R17
100kΩ
R18
100kΩ
R15
100kΩ
R16
100kΩ
R13
100kΩ
R14
100kΩ
R11
100kΩ
R12
100kΩ
191kΩ
10.0kΩ
0.47μF
VGON
25V/20mA
0.1μF
VIN
4.5V TO 5.5V
22μF
C12
220μF
C13
0.1μF
R10
10Ω
180kΩ
6.8kΩ
C10
0.1μF
324kΩ
31.6kΩ
0.22μF
0.22μF
VGOFF
-10V/50mA
0.033μF
TO VCOM
BACKPLANE
COMP
DRVN
FBN
REF
AGND
PGND
DRVP
FBP
SRC
COM
DEL
NEG1
NEG2
OUT2
OUT3
NEG4
OUT4
NEG5
OUT5
OUT1
DRN
CTL
SUP
BGND
POS1
POS2
POS3
POS4
POS5
MAX8795A
Figure 1. Typical Operating Circuit
DESIGNATIONDESCRIPTION22µF, 6.3V X5R ceramic capacitor (1210)
TDK C3225X5R0J227M22µF, 16V X5R ceramic capacitor (1812)
TDK C4532X5X1C226M3A, 30V Schottky diode (M-flat)
Toshiba CMS02200mA, 100V, dual ultra-fast diodes (SOT23)
DESIGNATIONDESCRIPTION3.0µH, 3A inductor
Sumida CDRH6D28-3R0200mA, 40V pnp bipolar transistor (SOT23)
Fairchild MMBT3906200mA, 40V npn bipolar transistor (SOT23)
Fairchild MMBT3904
Table 1. Component List
MAX8795A
TFT-LCD DC-DC Converter with
Operational Amplifiers
SUPPLIERPHONEFAXWEBSITEFairchild408-822-2000408-822-2102www.fairchildsemi.com
Sumida847-545-6700847-545-6720www.sumida.com
TDK847-803-6100847-390-4405www.component.tdk.com
Toshiba949-455-2000949-859-3963www.toshiba.com/taec
Table 2. Component Suppliers
Detailed DescriptionThe MAX8795A contains a high-performance step-up
switching regulator, two low-cost linear-regulator con-
trollers, multiple high-current operational amplifiers,
and startup timing and level-shifting functionality useful
for active-matrix TFT LCDs. Figure2 shows the
MAX8795A functional diagram.
Main Step-Up RegulatorThe main step-up regulator employs a current-mode,
fixed-frequency PWM architecture to maximize loop
bandwidth and provide fast transient response to
pulsed loads typical of TFT-LCD panel source drivers.
The 1.2MHz switching frequency allows the use of low-
profile inductors and ceramic capacitors to minimize
the thickness of LCD panel designs. The integrated
high-efficiency MOSFET and the IC’s built-in digital
soft-start functions reduce the number of external com-
ponents required while controlling inrush currents. The
output voltage can be set from VINto 18V with an exter-
nal resistive voltage-divider.
The regulator controls the output voltage and the power
delivered to the output by modulating the duty cycle (D)
of the internal power MOSFET in each switching cycle.
The duty cycle of the MOSFET is approximated by:
Figure 3 shows the functional diagram of the step-up
regulator. An error amplifier compares the signal at FB
to 1.233V and changes the COMP output. The voltage
at COMP sets the peak inductor current. As the load
varies, the error amplifier sources or sinks current to the
COMP output accordingly to produce the inductor peak
current necessary to service the load. To maintain sta-
bility at high duty cycles, a slope-compensation signal
is summed with the current-sense signal.
On the rising edge of the internal clock, the controller sets
a flip-flop, turning on the n-channel MOSFET and applying
the input voltage across the inductor. The currentthrough
the inductor ramps up linearly, storing energy in its
magnetic field. Once the sum of the current-feedbackVV
MAININ
MAIN≈−
STEP-UP
CONTROLLER
GATE-ON
CONTROLLER
SWITCH
CONTROL
GATE-OFF
CONTROLLER
REF
VCNVCP
VMAIN
PGND
AGND
DRVP
FBP
VCP
VGON
VCN
VGOFF
DEL
CTL
DRVN
FBN
NEG4
REF
POS4
NEG5
POS5
OUT4
OUT5
BGND
NEG2
POS2
OP3
POS3
OUT2
OUT3
POS1
OUT1
NEG1
SUP
COM
DRN
SRC
COMP
VIN
MAX8795A
OP2
OP1
OP5
OP4
