LM3492/LM3492Q Two-Channel Individual Dimmable LED Driver with Boost Converter and Fast Current Regulator
Literature Number: SNVS656B
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LM3492/LM3492Q
Two-Channel Individual Dimmable LED Driver with BoostConverter and Fast Current Regulator
General Description
The LM3492 integrates a boost converter and a two-channelcurrent regulator to implement a high efficient and cost effec-tive LED driver for driving two individually dimmable LEDstrings with a maximum power of 15W and an output voltageof up to 65V. The boost converter employs a proprietary Pro-jected-On-Time control method to give a fast transient re-sponse with no compensation required, and a nearly constantswitching frequency programmable from 200 kHz to 1 MHz.The application circuit is stable with ceramic capacitors andproduces no audible noise on dimming. The programmablepeak current limit and soft-start features reduce currentsurges at startup, and an integrated 190 mΩ, 3.9A N-ChannelMOSFET switch minimizes the solution size. The fast slewrate current regulator allows high frequency and narrow pulsewidth dimming signals to achieve a very high contrast ratio of1000:1 at a dimming frequency of more than 3 kHz. The LEDcurrent is programmable from 50 mA to 200 mA by a singleresistor.
To maximize the efficiency, Dynamic Headroom Control(DHC) automatically adjusts the output voltage to a minimum.DHC also facilitates a single BOM for different number of LEDin a string, which is required for backlight panels of differentsize, thereby reducing overall development time and cost.The LM3492 comes with a versatile COMM pin which servesas a bi-directional I/O pin interfacing with an external MCU forthe following functions: power-good, over-temperature, IOUTover- and under-voltage indications, switching frequency tun-ing, and channel 1 disabling. Other supervisory functions ofthe LM3492 include precise enable, VCC under-voltage lock-out, current regulator over-power protection, and thermalshutdown protection. The LM3492 is available in the thermallyenhanced eTSSOP-20 package.
rent RegulatorFeatures
Boost Converter:
■LM3492Q is an Automotive Grade Product that is AECQ100 grade 1 qualified
■Very wide input voltage ranged from 4.5V-65V■Programmable soft-start
■No loop compensation required
■Stable with ceramic and other low ESR capacitors with noaudible noise
■Nearly constant switching frequency programmable from200 kHz to 1 MHzCurrent Regulators:
■Programmable LED current from 50 mA to 200 mA
■1000:1 contrast ratio at a dimming frequency of more than3 kHz, minimum LED current pulse width is 300 ns
■Two individual dimmable LED strings up to 65V, total 15W(typically 28 LEDs @ 150 mA)
■Dynamic Headroom Control maximizes efficiency■Over-Power protection■±3% current accuracy
Supervisory Functions:■Precision enable
■COMM I/O pin for diagnostic and commands■Thermal shutdown protection
■Thermally enhanced eTSSOP-20 package
Applications
■Ultra-high contrast ratio 6.5”-10” LCD display backlight up
to 28 LEDs
■Automotive or marine GPS display
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LM3492/LM30116101
Connection Diagram
Top View
20-Lead Plastic eTSSOP (MXA20A)
30116102
Ordering Information
Order NumberLM3492MHLM3492MHXLM3492QMHLM3492QMHX
Package TypeExposed PadTSSOP-20
NSC PackageDrawingMXA20A
Supplied As
73 Units per Anti-Static Tube2500 Units on Tape and Reel73 Units per Anti-Static Tube2500 Units on Tape and Reel
Feature
AEC-Q100 Grade 1 qualifiedAutomotive Grade Productio
Flow*
*Automotive Grade (Q) product incorporates enhanced manufacturing and support processes for the automotive market, including defect detection methodologiReliability qualification is compliant with the requirements and temperature grades defined in the AEC-Q100 standard. Automotive grade products are identifwith the letter Q. For more information go to http://www.national.com/automotive.
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92/LM3492QPin123, 4567
NameENVINSWVOUTRTFB
DescriptionEnable
Input Supply VoltageSwitch Node
Output Voltage SenseFrequency ControlOutput Voltage Feedback
Application Information
Internally pull-up. Connect to a voltage higher than 1.63V to provide precisionenable for the device.
Supply pin to the device. Input range is 4.5V to 65V.Internally connected to the drain of the integrated MOSFET.
Sense the output voltage for nearly constant switching frequency control.An external resistor from the VOUT pin to this pin sets the switchingfrequency.
The output voltage is connected to this pin through a feedback resistor
divider for output voltage regulation. The voltage of this pin is from 1.05V to2.5V.
Signal Ground
1011
GNDIOUT2IOUT1CDHC
Analog Ground
Current Regulator Input of Channel 2Input of the current regulator of channel 2. The regulated current is
programmable (refer to the IREF pin).Current Regulator Input of Channel 1Input of the current regulator of channel 1. The regulated current is
programmable (refer to the IREF pin).Dynamic Headroom Control
An external capacitor connected to this pin sets the DHC sensitivity. Atstartup, a 120 µA internal current source charges an external capacitor toprovide a soft-start function.
An external resistor connected from this pin to ground programs theregulated current of the current regulator of channels 1 and 2.
This pin is open drain for various indications (power-good, over-temperature,IOUT over- and under-voltage) and command sending (switching frequencytuning and channel 1 disabling).
Current regulator ground. Must be connected to the GND pin for normaloperation. The LGND and GND pins are not internally connected.
Control the on/off of the current regulator of channel 1. This pin is internallypulled low by a 5 µA current. This pin also serves as a clock signal for latchinginput/output data of the COMM pin.
Control the on/off of the current regulator of channel 2. This pin is internallypulled low by a 5 µA current.
Integrated MOSFET ground. Must be connected to the GND pin for normaloperation. The PGND and GND pins are not internally connected.Nominally regulated to 5.5V. Connect a capacitor of larger than 0.47 µFbetween the VCC and GND pins.
Connect an external resistor from the ILIM pin to the VCC pin reduces peakcurrent limit. Connect the ILIM pin to the ground to obtain the maximumcurrent limit.
Thermal connection pad. Connect to a ground plane.
1213
IREFCOMM
Current Setting of the CurrentRegulator
Bi-directional Logic Communication
1415
LGNDGround of the Current Regulator
DIM1/CLKDimming Control of Channel 1
1617, 181920
DIM2PGNDVCCILIM
Dimming Control of Channel 2Power GroundLDO Regulator OutputPeak Current Limit Adjust
DAPDAPExposed Pad
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LM3492/LMIf Military/Aerospace specified devices are required,please contact the National Semiconductor Sales Office/Distributors for availability and specifications.VIN, RT, VOUT to GNDSW to GND
SW to GND (Transient)ILIM to GNDFB to GND
COMM, DIM1, DIM2, to GND
−0.3V to 67V−0.3V to 67V−2V (<100 ns)−0.3V to 0.3V−0.3V to 5V−0.3V to 6V
Human Body Model
Storage Temperature RangeJunctionTemperature (TJ)
±2kV
−65°C to +150°C150°C
(Note 1)
Operating Ratings
Supply Voltage (VIN)
Operation Temperature Range (TA)Thermal Resistance (θJA) (Note 3)
4.5V to 6−40°C to +125
32.7°C
Specification with standard type are for TA = TJ = +25°C only; limits in boldface ty
apply over the full Operating Junction Temperature (TJ) range. Minimum and Maximum are guaranteed through test, design orstatistical correlation. Typical values represent the most likely parametric norm at TJ = +25°C, and are provided for referencepurposes only. Unless otherwise stated the following conditions apply: VIN = 12V.SymbolVCC VCC-UVLOVCC-UVLO-HYSIINIIN-SDIVCCVCC-VOUTEnable InputVENVEN-HYSIEN-SHUTIEN-OPER
Current RegulatorVIREFVDHC50VDHC100VDHC200IOUT50IOUT100IOUT200IOUTOFFVIOUT50-MINVIOUT100-MINVIOUT200-MINVDIM-HIGHVDIM-LOW
IREF pin voltage
VIOUT under DHC at IOUT = 50 mAVIOUT under DHC at IOUT = 100 mAVIOUT under DHC at IOUT = 200 mACurrent Output under DHC at VIOUT =VDHC50
Current Output under DHC at VIOUT =VDHC100
Current Output under DHC at VIOUT =VDHC200
Leakage at Maximum Work VoltageMinimum Work Voltage, 50 mAMinimum Work Voltage, 100 mAMinimum Work Voltage, 200 mADIM Voltage HIGHDIM Voltage LOW
VIN = 4.5V to 65VRIREF = 25 kΩRIREF = 12.5 kΩRIREF = 6.25 kΩ
RIREF = 25 kΩ, VIOUT = VDHC50RIREF = 25 kΩ, VIOUT = VDHC50RIREF = 12.5 kΩ, VIOUT = VDHC100RIREF = 12.5 kΩ, VIOUT = VDHC100RIREF = 6.25 kΩ, VIOUT = VDHC200RIREF = 6.25 kΩ, VIOUT = VDHC200VDIM = 0, VIOUT = 65V
RIREF = 25 kΩ, IOUT = 0.98 x IOUT50RIREF = 12.5 kΩ, IOUT = 0.98 x IOUT100RIREF = 6.25 kΩ, IOUT = 0.98 x IOUT200
1.17
1.2311.2561.2810.1600.2250.2900.380.8147.546.59796194192
0.480.995050100100200200 0.10.20.4
0.581.1752.553.510310420620850.150.350.65 0.7
EN pin input thresholdEN pin threshold hysteresisEnable Pull-up Current at shutdownEnable Pull-up Current during operation
VEN risingVEN fallingVEN = 0VVEN = 2V
1.55
1.63194240
1.71
Parameter
VCC pin output voltage
VCC pin under-voltage lockout threshold(UVLO)
VCC pin UVLO hysteresisIIN operating current
IIN operating current, Device shutdownVCC pin current limit (Note 4)
Conditions
CVCC = 0.47 µF, no loadICC = 2 mAVCC increasingVCC decreasingNo switching, VFB = 0VVEN = 0VVCC = 0V
Min4.74.73.56 183.5
Typ5.55.53.783103.630304.1
Max6.36.34.00 5.295 4.7
Start-Up Regulator, VCC
Electrical Characteristics
U
VCC pin output voltage when supplied byVIN = Open, ICC = 1 mA, VOUT = 18VVOUT
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Boost ConverterICDHC-SRCICDHC-SINKICDHC-LEAKAGEICL-MAXICL-HALFRDS(on)VFBTH-PWRGDIFBton ton-min-ILIMtoff
COMM PINVIOUT-OVVCOMM-LOWILEAK-FAULTTOTMTOTM-HYSTSDTSD-HYS
IOUT pin over-voltage thresholdCOMM pin at LOWCOMM pin Open LeakageOver-temperature indication
Over-temperature indication hysteresisThermal shutdown temperature
COMM goes LOW during VIOUT rising,other VIOUT = 1.2V5 mA into COMMVCOMM = 5VTJ risingTJ fallingTJ rising
5.6
6.7 1351516520
7.80.75
VVµA°C°C°C°C
CDHC pin source currentCDHC pin sink currentCDHC pin leakage current
Integrated MOSFET peak current limitthreshold
VCDHC = 1.6V, VFB = 3V, VIOUT = 0V, DIM= High
VCDHC = 1.6V, VFB = 3V, VIOUT = 3V, DIM= High
DIM = Low, VCDHC = 2.6V
3.3
605653.92.00.192.25 1460800550350145145
4.5 0.43 1 350
µAµAnAAAΩVµAnsnsnsnsnsns
92/LM3492QHalf integrated MOSFET peak current limitRILIM = 11 kΩthreshold
Integrated MOSFET RDS(on)Power-Good FB pin thresholdFeedback pin input currentON timer pulse width
ISW = 500 mA VFB = 3V
VIN = 12V, VOUT = 65V, RRT = 300 kΩVIN = 24V, VOUT = 32.5V, RRT = 300 kΩVIN = 12V, VOUT = 65V, RRT = 100 kΩVIN = 24V, VOUT = 32.5V, RRT = 100 kΩ
ON timer minimum pulse width at current limit
OFF timer pulse width
Thermal Protection
Thermal shutdown temperature hysteresisTJ falling
Note 1:Absolute Maximum Ratings are limits which damage to the device may occur. Operating ratings are conditions under which operation of the device isintended to be functional. For guaranteed specifications and test conditions, see the electrical characteristics. Thermal shutdown might occur within ambientoperating temperature range as junction temperature rises above TSD level, customer should refer to efficiency data and thermal resistance data to estimate thejunction temperature to ambient temperature delta.
Note 2:The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.
Note 3:The θJA is measured on a 4-layer standard JEDEC thermal test board with 12 vias, no air flow and 1W power dissipation. Thermal shutdown will occurif the junction temperature exceeds 165°C. The maximum power dissipation is a function of TJ(MAX), θJA and TA. The maximum allowable power dissipation at anyambient temperature is PD = (TJ(MAX) – TA) /θJA.
Note 4:VCC provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading.
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LM3492/LMUnless otherwise specified the following conditions apply: TJ = 25°C, VIN = 12V with configuration in typical application circuit fILED = 200 mA shown in this datasheet.
Quiescent Current, IIN vs VIN
VCC vs IVCC
3011611130116112
VCC vs VINSwitching Frequency, fSW vs VIN
3011611330116114
ILED Regulation vs TemperatureRDS(on) vs Temperature
3011611530116116
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(ILED = 0.2A)
92/LM3492Q30116117
30116118
Power Up (ILED = 0.2A)Enable Transient (ILED = 0.2A)
3011611930116120
Steady State Operation (ILED = 0.2A)
LED 50% Dimming
(ILED = 0.2A, Dimming frequency = 200Hz)
30116121
30116122
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LM3492/LM(ILED = 0.2A, Dimming frequency = 200Hz)(ILED = 0.2A, Dimming frequency = 3.33 kHz)
3011612330116124
Simplified Functional Block Diagram
30116103
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92/LM3492QThe LM3492 integrates a boost converter and a two-channelcurrent regulator to implement a high efficient and cost effec-tive LED driver for driving two individually dimmable LEDstrings with a maximum power of 15W and an output voltageof up to 65V. The boost converter provides power for the LEDstrings, and the current regulator controls the dimming of theLED strings individually. The LM3492 integrates an N-chan-nel MOSFET switch and a two-channel current regulator inorder to minimize the component count and solution size.The boost converter of the LM3492 employs a Projected On-Time (POT) control method to determine the on-time of theMOSFET with respect to the input and output voltages andan external resistor RRT. During the on-period, the boost in-ductor is charged up, and the output capacitor is dischargedto provide power to the output. A cycle-by-cycle current limit(which is 3.9A typically and programmable by an external re-sistor) is imposed on the MOSFET for protection. After the on-period, the MOSFET is turned off such that the boost inductoris discharged. The next on-period is started when the voltageof the FB pin is dropped below a threshold which is deter-mined by Dynamic Headroom Control (DHC) and is rangedfrom 1.05V to 2.5V (DHC affects the threshold only when theDIM1 and/or DIM2 pins are high). The boost converter underPOT control can maintain the switching frequency nearly con-stant so that the switching frequency depends on only RRT(Figure 1). Also, POT control requires no compensation circuitand gives a fast transient response of the output voltage.
in the presence of the indications. Other useful features in-clude thermal shutdown, VCC under-voltage lock-out, andprecision enable. The LM3492 is available in the thermallyenhanced eTSSOP-20 package.
LDO Regulator
A 5.5V LDO regulator is integrated in the LM3492. For stabil-ity, an external capacitor CVCC of more than 0.47 µF shouldbe connected between the VCC and GND pins. The currentlimit of the LDO is typically 30 mA. It can be used to pull-upthe open-drain COMM pin with an external resistor, and injectcurrent to the ILIM pin to adjust the current limit of the inte-grated MOSFET. When the voltage on the VCC pin (VCC) ishigher than the under-voltage lock-out (UVLO) threshold of3.78V, the LM3492 is enabled and the CDHC pin sources acurrent to charge up an external capacitor CCDHC to providea soft-start function.
Enable and Disable
To enable the LM3492, the voltage on the EN pin (VEN) mustbe higher than an enable threshold of typically 1.63V. If VENis lower than 1.43V, the LM3492 is shutdown. In this case, theLDO regulator is turned off and the CDHC pin is internallygrounded. The EN pin is internally pulled up. After enable, theEN pin is pulled up by a 40 µA current source. If the EN pin isconnected to low such that the LM3492 is shutdown, the pull-up current is reduced to 2 µA. These take the advantages thatthe LM3492 can effectively avoid false disabling by noise dur-ing operation, and minimize power consumption during shut-down. The enable threshold is precise such that it can be usedto implement an UVLO function for the input voltage as shownin Figure 2. The input voltage can be connected to the EN pinthrough a resistor divider consists of REN1 and REN2. This canensure that the LM3492 is operated after the input voltagereaches a minimum require value VIN(EN), which can be cal-culated by the following equation:
VIN(EN) = 1.63V(1 + REN1/ REN2)
(1)
A zener diode DEN should be placed between the EN andGND pins to keep VEN below its absolute maximum causedby the increase of the input voltage.
30116125
FIGURE 1. Switching Frequency
The two-channel current regulator of the LM3492 is fast re-sponse so that it can allow very high contrast ratio (1000:1 at3 kHz LED dimming frequency, minimum pulse width of thedimming signal is 300 ns). The two channels are dimmableindividually. Channel 1 of the current regulator can be dis-abled by a digital command send through the COMM pin. Inthis case, the DIM1 pin can serve only as a clock signal forthe data flow of the COMM pin. The power dissipated by thecurrent regulator is adaptively minimized by Dynamic Head-room Control in order to maximize efficiency.
The LM3492 can be applied in numerous applications likeautomotive LCD backlight panels. It can operate efficiently forinputs as high as 65V. Diagnostic functions including powergood indication, over-temperature indication, IOUT over- andunder-voltage indications facilitate the interface of the
30116104
FIGURE 2. Input Voltage UVLO Implemented by Precision
EnableOnce the EN pin is pulled low, the LM3492 will perform thefollowing functions: reset IOUT over- and under-voltage indi-cations and the corresponding COMM bit pattern, resume theswitching frequency tuning to the normal frequency, and re-sume channel 1 of the current regulator if it is disabled. Pullingthe EN pin low for a short period of about 200 ns can achieve
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分销商库存信息:
NATIONAL-SEMICONDUCTORLM3492MH/NOPBLM3492QMH/NOPBLM3492QMHX/NOPB
LM3492MHX/NOPB
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