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VAS1260 数据手册

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preliminary
VAS1260
60V/1.2A LED Driver with Internal Switch
General Description
The VAS1260 is a continuous mode inductive step-down converter, designed for driving single or multiple series connected LEDs efficiently from a voltage source higher than the LED voltage. The device operates from an input supply between 5V and 60V, and provides an externally adjustable output current of up to 1.2A. The VAS1260 includes the output switch and a high-side output current sensing circuit, which uses an external resistor to set the nominal average output current. Output current can be adjusted below the set value, by applying an external control signal to the ‘ADJ’ pin. The device operates over the -40°C to +85°C temperature range and is available in SOT89-5 package.
Features
Simple low parts count Internal 60V NMOS switch 1.2A output current PWM dimming High efficiency (up to 97%) Wide input voltage range: 5V to 60V Over Temperature protection Up to 1MHz switching frequency Inherent open-circuit LED protection Typical 5% output current accuracy
Ordering Information
Order Number VAS1260IB05E
I: Industry, -40~85℃ 05 : Pin Number
Package Type SOT89-5
B: SOT E: ROHS
Temp. Range -40 °C to 85°C
Pin Configuration
SOT89-5
Application
Architectural, Industrial, Ambient and Car Lighting LED MR16, MR111 PAR and other LED Bulbs
Typical Application Circuit
VAS1260, ver0.2
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VAS1260
Block Diagram
PIN Description
Name LX GND PIN NO. 1 2 Description Drain of the internal NMOS Ground Multi-function On/Off and brightness control pin: ? Drive to voltage below 0.5V to turn off output current and for over 30ms to shutdown the device ? Leave floating for normal operation, output current IOUTNOM=0.1/RSNS) ? Drive with a PWM signal to adjust output current Current Sense Input Positive Supply Voltage Input. Bypass with a 1μF or higher value capacitor to GND
ADJ
3
SNS VIN
4 5
VAS1260, ver0.2
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VAS1260
Absolute Maximum Ratings(Note1)
Parameters VIN, SNS, ADJ, LX to GND VIN to SNS Operating temperature range Junction temperature Storage temperature range ESD human body model Maximum Ratings -0.3V to 66V -0.3V to +0.3V -40°C to +85°C -40°C to +150°C -65°C to +150°C 2000V
Note 1:Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance.
Electrical Characteristics
Typical case(Note2): VCC=12V, TA=25°C(unless otherwise specified)
Symbol VIN ICC ISD UVLO Parameter Input voltage range Quiescent current Shutdown supply current Under-voltage Lockout ADJ floating, all external devices open VADJ =0V Condition spec Min. 5 350 100 3.5 0.2 Measured on SNS pin with respect to VIN, ADJ pin floating VIN-VSNS=100mV Typ. Max. 60 600 150 3.7 Unit V μA μA V V
UVLO-HYS UVLO Hysteresis SENSE COMPARATOR VSNS VSNS_HYS ISNS TPD Mean current sense threshold voltage(defines LED current setting accuracy) Sense threshold hysteresis Current Sense Input Current Internal comparator Propagation Delay PWM dimming range PWM Dimming Input-Voltage-High PWM Dimming Input-Voltage-Low PWM Dimming Maximum Turn-Off time Continuous LX switch current 0. 5 100 95
100 ±15% 5 50
105
mV
μA ns
DIMMING INPUT FPWM VIH VIL TPWMOFF ILXmean 20,000 1.5 15 1.2 Hz V V ms A
VAS1260, ver0.2
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RDSON ILX(leak) TONmin TOFFmin FLXmax LX switch ‘on’ resistance LX switch leakage current Recommend maximum turn-on time Recommend minimum turn-off time Recommend maximum operation frequency Thermal shutdown temperature Thermal shutdown hysteresis 100 100 1
preliminary
0.3
VAS1260
0.5 1 ? μA ns ns MHz
THERMAL SHUTDOWN TSD TSDhys 170 20 ℃ ℃
Note 2: Production testing of the device is performed at 25°C. Functional operation of the device and parameters specified over other temperature range, are guaranteed by design, characterization and process control.
VAS1260, ver0.2
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VAS1260
Application Information
The VAS1260 is a step-down, constant-current, high-brightness LED(HBLED) driver. These devices operate from a 5V to 60V input voltage range and provide up to 1.2A continuous LX switch current. A high-side current-sense resistor sets the output current. ADJ allows for 100Hz~20KHz PWM signal dimming. The high-side current-sense scheme and on-board current setting circuitry minimize the number of external components while delivering LED current with a ±5% accuracy, using a 1% sense resistor. 1. Under-Voltage Lockout (UVLO) The VAS1260 include a 3.7V under-voltage lockout (UVLO) with 200mV hysteresis. When VIN falls below 3.5V, internal NMOS switches off and once VIN is 3.7V or higher, internal NMOS switches on. 2. ADJ Input The VAS1260 allows PWM dimming. When an external PWM signal is added at the ADJ input. A logic level below 0.5V at ADJ forces the internal NMOS off, turning off the LED current. To turn the LED current on, the logic level at ADJ must be at least 1.5V. When ADJ is below 0.5V for over 30ms, the device will shut down and has less dissipation . 3. Over-Heating Issue It is possible that the chip may be overheating caused by the unreasonable circuit design or operation, and the VAS1260 solve the issue by: 1) If the VAS1260 die temperature rises to 120℃(IC surface is about 90℃), LED current starts to decrease gradually. 2)If the temperature continues to increase to 170℃, VAS1260 enter thermal shutdown mode. When the temperature drops to 150℃, VAS1260 re-starts to work. 4. Selecting RSNS to Set the LED Current The VAS1260 feature a programmable LED current using a resistor connected between VIN and SNS. Use the following equation to calculate the sense resistor:
0T
RSNS =
0 .1 I LED
The table below gives values of nominal average output current for several values of current setting resistors (RSNS) in the typical application circuit shown on page 1.
RSNS (?) 0.5 0.3 0.1 nominal average output current(mA) 200 333 1000
5. Current Regulator Operations The VAS1260 regulate the LED output current using an input comparator with hysteresis (Show in the figure bellow). As the current through the inductor ramps up and the voltage across the sense resistor reaches the
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preliminary
VAS1260
upper threshold, turning off the internal NMOS. The NMOS turns on again when the inductor current ramps down through the freewheeling diode until the voltage across the sense resistor equals the lower threshold. Use the following equation to determine the operating frequency:
FSW =
(VIN ? VOUT ) × VOUT
VIN × ?I × L
Where ?I is the coil peak-peak ripple
T = 1 F
SW
6. Inductor selection Recommended inductor values for the VAS1260 are in the range 47μH to 470μH. Higher values of inductance are recommended at higher supply voltages and low output current in order to minimize errors due to switching delays, which result in increased ripple and lower efficiency. Higher values of inductance also result in a smaller change in output current over the supply voltage range. The inductor should be mounted as close to the chip as possible with low resistance connections to the LX and VIN pins. The chosen coil should have a saturation current higher than the peak output current and a continuous current rating above the required mean output current. It is recommended to use inductor with saturation current larger than 500mA for 350mA output current. The inductor value should be chosen to maintain operation duty cycle and switch ‘on/off’ times within the specified limits over the supply voltage and load current range. Following information can be used as a guide. Internal NMOS Switch ‘on’ time:
TON = L × ?I VIN ? VLED ? I AVG (RS + RL + RDSON )
Note that : TON>100ns Internal NMOS Switch ‘off’ time:
VAS1260, ver0.2
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TOFF =
VLED
L × ?I + VD + I AVG ( RS + RL )
Note that : TOFF>100ns Where: L is the coil inductor (H) RL is the resistance (?) IAVG is the required LED current (A) ?I is the coil peak-peak ripple current (A) (internally set to 0.2 × I AVG ) VIN is the supply voltage (V) VLED is the total LED forward voltage (V) R DSON is the switch resistor of NMOS (?) VD is the diode forward voltage at the required load current (V) Example: For VIN=12V, L=220μH, RS=0.3?, RL=0.64?, RDSON=0.3?, IAVG=333mA and VD=0.36V
R
TON =
( 220 × 10
?6
× 0.067 )
(12 ? 3.4 ? 0.413)
= 1.8μ s = 3.61μ s
TOFF =
( 220 ×10
?6
× 0.067 )
(3.4 + 0.36 + 0.313)
This gives an operating frequency of 184.8 kHz and a duty circle of 0.33. 7. LED Current Ripple The LED current ripple is equal to the inductor current ripple. In cases when a lower LED current ripple is needed, a capacitor can be placed across the LED terminals. 8. Capacitor selection A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in series with the supply source impedance and lowers overall efficiency. This capacitor has to supply the relatively high peak current to the coil and smooth the current ripple on the supply. If the source is DC supply, the capacitor is decided by the ripple of the source, the value is given by:
C min = I OUT × TON ?U max
IOUT is the value of output current, ?Umax is the ripple of power supply. TON is the ‘ON’ time of internal NMOS. The value is normally 2 times of the minimum value. Recommend a 100μF capacitor or larger. 9. Schottky Diode Selection The Schottky diode breakdown voltage should high enough to withstand the maximum operating voltage and its forward current rating must be higher than the maximum LED current. 10. PCB Layout Careful PCB layout is critical to achieve low switching losses and stable operation. Use a multilayer board whenever possible for better noise immunity. Minimize ground noise by connecting high-current ground returns, the input bypass-capacitor ground lead, and the output-filter ground lead
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VAS1260
to a single point (star ground configuration). In normal operation, there are two power loops. One is formed when the internal NMOS is on and the high current flows through VIN—RSNS—LEDs— Inductor—LX—GND. The other loop is formed when the internal NMOS is off when the high current circulates through RSNS—LEDs—Inductor—Schottky diode. To minimize noise interaction, each loop area should be as small as possible. Place RSNS as close as possible to the input filter and VIN. For better noise immunity, a Kelvin connection is strongly recommended between SNS and RSNS.
VAS1260, ver0.2
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VAS1260
Package Information (SOT89-5)
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VAS1260
Classification Reflow Profiles
Profile Feature Preheat & Soak Temperature min (Tsmin) Temperature max(Tsmax) Time (Tsmin to Tsmax) (ts) Average ramp-up rate (Tsmax to Tp ) Liquidous temperature (TL) Time at liquidous (tL) Peak package body temperature (Tp)* Time (tp)* * within 5°C of the specified classification temperature (Tc) Average ramp-down rate (Tp to Tsma x) Time 25 °C to peak temperature Pb-Free Assembly 150°C 200°C 60 -120 seconds 3°C/second max. 217 °C 60 -150 seconds Max 260°C Max 30 seconds 6°C/second max. 8 minutes max
Classification Profile
! CAUTION
Storage Conditions 1) This product should be used within 12 months after delivered. Store in manufacturer’s package keeping the seal of aluminum coated baggage or tightly re-closed box with the following conditions. [Temperature: 8℃…30℃, Humidity: 30%...70%R.H.] 2) Keep the seal of aluminum coated baggage immediately before usage. 3) After breaking the seal of aluminum coated baggage, this product should be used within 1 week on the following conditions.[Temperature:≤30℃, Humidity:≤60%R.H.]
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