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AL8400
0.2V LINEAR LED DRIVER CONTROLLER
Description
The AL8400 is a 5-terminal adjustable Linear LED driver controller offering excellent temperature stability and output handling capability. The AL8400 simplifies the design of linear and isolated LED drivers. With its low 0.2V FB pin, it controls the regulation of LED current with minimal power dissipation when compared to traditional linear LED drivers. This makes it ideal for medium to high current LED driving. The AL8400 open-collector output can operate from 0.2V to 18V enabling it to drive external MOSFET and Bipolar transistors. This enables the MOSFET and Bipolar selection to be optimised for the chosen application. It also provides the capability to drive longer LED chains, by tapping VCC from the chain, where the chain voltage may exceed 18V. It is available in the space saving low profile SOT353 package.
Pin Assignments
(Top View)
E1
1 2 3
5
OUT
GND
AL8400
4
FB
VCC
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Features
* * * * * *
*
Applications
* * * * Isolated offline LED converters Linear LED driver LED signs Instrumentation illumination
Low reference voltage (VFB = 0.2V) -40 to 125C temperature range 3% Reference voltage tolerance at 25C Low temperature drift 0.2V to 18V open-collector output High power supply rejection (> 45dB at 300kHz)
Typical Application Circuit
AL8400
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AL8400
0.2V LINEAR LED DRIVER CONTROLLER
Functional Block Diagram
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Figure 1. Block Diagram
Pin Descriptions
Pin Number 1 2 3 4 5 Name E1 GND VCC FB OUT Function Emitter connection. Connect to GND. Analog Ground. Ground return for reference and amplifier. Connect to E1. Supply Input. Connect a 0.47F ceramic capacitor close to the device from VCC to GND. Feedback Input. Regulates to 200mV nominal. Output. Connect a capacitor close to device between OUT and GND. See the Applications Information section.
Absolute Maximum Ratings
Symbol VCC VOUT VFB VE1 TJ TST Characteristics Supply voltage relative to GND OUT voltage relative to GND FB voltage relative to GND E1 voltage relative to GND Operating junction temperature Storage temperature Values 20 20 20 -0.3 to+0.3 -40 to 150 -55 to 150 Unit V V V V C C
These are stress ratings only. Operation outside the absolute maximum ratings may cause device failure. Operation at the absolute maximum rating for extended periods may reduce device reliability.
Package Thermal Data
Package SOT353 JA 400C/W PDIS TA = 25C, TJ = 150C 310mW
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AL8400
0.2V LINEAR LED DRIVER CONTROLLER
Recommended Operating Conditions
Symbol VCC VOUT IOUT TA Parameter Supply voltage range (-40 to 125C) OUT voltage range OUT pin current Operating ambient temperature range Min 2.2 0.2 0.3 -40 Max 18 18 15 125 Units V mA C
Electrical Characteristics (TA = 25C, Vdd = 3V; unless otherwise specified) NEW PRODUCT
Operating conditions: TA = 25C, VCC= 12V, VOUT = VFB, IOUT = 1mA unless otherwise stated (Note 1). Symbol Parameter Conditions Min. VFB Feedback voltage IOUT = 1 to 15mA VCC = 2.2V to 18V TA = 25C TA = -40 to 125C TA = 25C TA = -40 to 125C TA = 25C TA = -40 to 125C 0.1 0.194 0.190 3.1 Typ. 0.2 Max. 0.206 0.210 6 10 1.5 2 2 3 -45 -200 0.48 0 1 1.5 0.1 1 0.25 45 600 4500 0.4 0.6 Units V mV mV mV nA mA A dB kHz mA/V
FBLOAD Feedback pin load regulation FBLINE FBOVR IFB ICC IOUT(LK) ZOUT PSRR BW G
Note:
Feedback pin line regulation Output voltage regulation FB input bias current Supply current OUT leakage current Dynamic Output Impedance Power supply rejection ratio Amplifier Unity Gain Frequency Amplifier Transconductance
VOUT = 0.2V to 18V, IOUT =1mA TA = 25C (Ref. Figure 1) TA = -40 to 125C VCC = 18V VCC = 2.2V to 18V, IOUT =10mA VCC = 18V, VOUT = 18V, VFB =0V IOUT = 1 to 15mA f < 1kHz f = 300kHz, VAC= 0.3VPP TA = 25C TA = -40 to 125C TA = 25C TA = -40 to 125C TA = 25C TA = 125C TA = 25C TA = -40 to125C TA = 25C TA = 25C TA = 25C
1. Production testing of the device is performed at 25 C. Functional operation of the device and parameters specified over the operating temperature range are guaranteed by design, characterisation and process control.
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AL8400
0.2V LINEAR LED DRIVER CONTROLLER
Typical Characteristics
4
TA = 25C VCC = 12V VOUT = VFB TA = 25C IOUT = 1mA VOUT = VFB
Output Voltage Change (mV)
Output Voltage Change (mV)
3
0
2
1
-0.05
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0
-1 0 2 4 6 8 10 Load current (mA) 12 14 16
-0.1
0 2 4 6 8 10 12 14 16 18 20
VCC (V)
Load regulation
0.6 TA = 25C VOUT = VFB Supply Current (mA) 0.6 TA = 25C VOUT = VFB
Line regulation
0.55 Supply Current (mA)
0.55
0.5
IOUT = 15mA
0.5
VCC=18V
0.45 IOUT = 10mA 0.4
0.45 VCC=12V 0.4 VCC=2.2V
IOUT = 1mA
0.35
0.35
0.3 0 2 4 6 8 10 VCC (V) 12 14 16 18 20
0.3 0 2 4 6 8 10 Load current (mA) 12 14 16
Supply current with input voltage
1.5
VCC = 12V IOUT = 1mA VOUT = VFB
FB input current (nA)
Supply current with load current
-40 VCC = 12V IOUT = 1mA VOUT = VFB
1 Output Voltage Change (mV)
-45
0.5
0
-50
-0.5
-55
-1
-1.5 -40 -25 -10 5 20 35 50 65 Ambient Temperature (C) 80 95 110 125
-60 -60 -40 -20 0 20 40 60 Ambient Temperature (C) 80 100 120 140
OUT voltage change with Temperature
FB input current with Temperature
AL8400
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0.2V LINEAR LED DRIVER CONTROLLER
Typical Characteristics (Continued)
210 208 206 204 Feedback Voltage (mV) 202 200 198 196 194 192 190 4 6 8 10 12 Supply Voltage (V) 14 16 18 ILED = 150mA TA = 25C One LED MOSFET = DMN6068SE ILED = 350mA
210 208 Feedback Voltage (mV) 206 204 202 200 198 196 194 192 190 4 6 8 10 12 Supply Voltage (V) 14 16 18 ILED = 150mA TA = 25C One LED Transistor = FZT690B (Min HFE ~500) ILED = 350mA
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MOSFET driving
Bipolar transistor driving
Application Information
Description
The AL8400 uses its FB pin to sense the LED current through an external resistor RSET. An external pass element consists of an NPN transistor or N-channel MOSFET. The pass element is used to regulate the LED's current and is driven from the AL8400's open collector OUT pin. An external resistor, RB, is required to be connected from the OUT pin to VCC. This resistor supplies the output bias current of the AL8400 together with any current which the pass element requires.
Bipolar transistor as the pass element
For driving at currents in the region of about 50mA to about 400mA, the recommended NPN is DNLS320E in the SOT223 package. The high DC current gain of the DNLS320E is useful in this application, in order to minimise the current in RB. The design procedure is as follows, referring to Figure 2.
Figure 2. Application Circuit Using Bipolar Transistor
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0.2V LINEAR LED DRIVER CONTROLLER
Application Information (Continued)
Bipolar transistor as the pass element (Continued)
There are two important equations for the circuit: LED circuit path: 1..... VCC = (VLED + VCE + VREF) Control drive circuit path 2..... VCC = (VRB + VBE + VREF) The maximum total LED voltage plus the reference voltage determines the minimum supply voltage. Substituting into equation 1 yields:
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VCC min = VLED + VCEsat + VREF
For a bipolar transistor the voltage (VRB) across bias resistor RB consists of the base current of Q2 and the output current of the AL8400. So rearranging equation 2 yields the boundaries for allowable RB values:
RB max =
VCC min - VBE max - VREF IOUT min + IB max IB min =
R B min =
VCC max - VBE min - VREF IOUT max + IB min
where IBmax is the maximum transistor base current
where IBmin is the minimum transistor base current
IB max
I = LED where hFEmin is the minimum DC hFE min
ILED where hFEmax is the maximum DC current gain of hFE max
current gain of the transistor.
the transistor.
Finally, the bipolar selection is also influenced by the maximum power dissipation PTOT = ILED * (VCC - VLED - VREF) = ILED * VCE Since this determines the package choice (JA) in order to keep the junction temperature below the maximum value allowed. TJ = TA + PTOT * JA
Bipolar Example
The driver is required to control 2 series connected LEDs at 150mA 10%, each having a forward voltage of 3V minimum and 3.6V maximum. Hence the minimum operating supply voltage is 3.6*2 + 0.2 = 7.4V. The actual supply voltage given is 8V 5%, i.e. 7.6V minimum. We will use the DNLS320E bipolar transistor (Q2). The DNLS320E datasheet shows: hFEmin is 500 @ IC = 100mA, 400 @ IC = 2A, The datasheet graph shows a very slow variation at his current, so a value of 500 is appropriate. 150 = 0.3mA Then IB max = 500 The minimum recommended IOUT for AL8400 is 0.3mA and the maximum VBE, according to the DNLS320E datasheet graph, is approximately 0.8V at -55C. From these the maximum allowed bias resistor value is: 7 .6 - 0 .8 - 0 .2 = 11k RB max = 0.0003 + 0.0003 To ensure that the output capability of the AL8400 is not exceeded at maximum VIN, maximum hFE and minimum VBE, these values should be substituted back into the RB equation to determine the minimum allowable value for RB. hFEmax is about 1200 @ IC = 100mA, and a temperature of 85C which results in: 150 = 0.125mA IB min = 1200
AL8400
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AL8400
0.2V LINEAR LED DRIVER CONTROLLER
Application Information (Continued)
Bipolar Example (Continued)
The maximum recommended IOUT for AL8400 is 15mA. The minimum VBE, according to the DNLS320E datasheet graph, is approximately 0.4V at 85C and assuming VCCmax = 8.4V, then the bias resistor value is:
RB min = 8 .4 - 0 .4 - 0 .2 = 516 This is less than 11k and so the AL8400 output current is within its ratings. 0.015 + 0.000125
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The value of RSET is VREF/ILED so: RSET = 0.2/0.15 = 1.333 1.3 is practical.
Finally, the maximum power dissipation of the external bipolar transistor is: PTOT = ILED * VCEMAX = ILED * (VCC - VLED_MIN - VREF) = 0.27W
This determines the package choice (JA) in order to keep the junction temperature of the bipolar below the maximum value allowed. TJ = TA + PTOT * JA = TA + 0.27*125 = TA + 33.75C
N-channel MOSFET as the pass element
Alternatively, an N-channel MOSFET may be used in the same configuration. The current in RB is then reduced compared to the case in which the bipolar transistor is used. For LED currents up to about 400mA a suitable MOSFET is DMN6068SE in the SOT223 package. The design procedure is as follows, referring to Figure 3.
Figure 3. Application Circuit Using MOSFET
The equations (1 and 2) for the bipolar transistor are transformed into: LED circuit path: 1..... VCC = (VLED + VDS + VREF) Control drive circuit path 2..... VCC = (VRB + VGS + VREF)
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0.2V LINEAR LED DRIVER CONTROLLER
Application Information (Continued)
N-channel MOSFET as the pass element (Continued)
The maximum total LED voltage plus the reference voltage determines the minimum supply voltage. Substituting into equation 3 yields:
VCC min = VLED + VDSMIN + VREF
The MOSFET DC gate current is negligible, so the bias resistor RB has only to provide the minimum output current of the AL8400. So rearranging equation 4 yields the boundaries for allowable RB values:
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R B min =
VCC max - VGS min - VREF IOUT max
RB max =
VCC min - VGS max - VREF IOUT min
Where IOUTmax is the AL8400 maximum output current
Where IOUTmin is the AL8400 minimum output current
Note that in the case of a single LED, the MOSFET gate-source voltage may be too high for operation over the desired supply voltage range. If the gate source voltage at the operating current is VGSMAX, we must have: VRBmin + VGSmax + VREF < VCC where VRBmin is the minimum voltage drop across RB. VRBmin is determined by the operating voltage range. At the top of the range, the current is required to be not greater than 15mA. The supply voltage is usually the LED voltage plus a margin for transistor saturation voltage, plus VREF. The bias amounts to the voltage across RB plus VREF (0.2V). Therefore the use of the MOSFET may not be practical for driving a single LED if the VGS is too high. Then either a MOSFET with lower VGS must be selected, or a bipolar NPN device must be used. Finally, the MOSFET selection is also influenced by the maximum power dissipation PTOT = ILED * (VCC - VLED - VREF) = ILED * VDS Since this determines the package choice (JA) in order to keep the junction temperature below the maximum value allowed. TJ = TA + PTOT * JA
MOSFET Example
The driver is required to control 2 series connected LEDs at 150mA 10%, each having a forward voltage of 3V minimum and of 3.6V maximum. Hence the minimum operating supply voltage is 3.6*2 + 0.2 = 7.4V. The actual supply voltage given is 8V 5%, i.e. 7.6V minimum. We will use the DMN6068SE N-channel MOSFET (Q2), The minimum recommended Iout for AL8400 is 0.3mA. The maximum VGS is not stated explicitly, but from the datasheet graphs it is expected to be approximately 3.8V at -50C. (Here we have used the graphs of Typical Transfer and Normalised VGS(th) versus temperature.) So RBmax = (7.6 - 3.8 - 0.2) / 0.0003 = 12k
To ensure that the output capability of the AL8400 is not exceeded at maximum VIN and minimum VGS these values should be substituted back into the RB equation to determine the minimum allowable value for RB. The maximum recommended IOUT for the AL8805 is 15mA. The minimum VGS is about 1V, and assuming VCCmax = 8.4V: RBmin =
8 .4 - 1 - 0 .2 = 480 0.015
This is less than 12k and so the AL8400 output current is within its ratings.
The value of RSET isVREF/ILED RSET = 0.2/0.15 = 1.333 1.3 is practical.
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AL8400
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AL8400
0.2V LINEAR LED DRIVER CONTROLLER
Application Information (Continued)
MOSFET Example (Continued)
Finally, the maximum power dissipation of the external MOSFET is: PTOT = ILED * VDSMAX = ILED * (VCC - VLEDMIN - VREF) = 0.27W
This determines the package choice (JA) in order to keep the junction temperature below the maximum value allowed. TJ = TA + PTOT * JA = TA + 0.27*62.5 = TA + 16.86C
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Stability
In order to maintain the stability of the current control loop, a capacitor, CL, is required to be connected from the OUT pin to Ground. The value is determined by the minimum time constant, CLRB 1ms. For example if RB = 10k, then CL must be 0.1F or greater. The capacitor type is recommended to be X7R ceramic. For best stability a power supply decoupling capacitor, CD is recommended, 0.1F minimum, X7R ceramic, connected between VCC and Ground.
OFFLINE LED LAMPS
The configuration of the AL8400 also makes it suitable for controlling the current of an offline (mains) isolated LED lamp by way of an opto-coupler to drive the feedback pin of the primary-side switching controller. The current sensing of the LED current is done via RSET but the OUT pin now drives the cathode of the diode in the optocoupler. See Figure 4 below.
Figure 4. Off-line LED Drive Application of AL8400 AL8400
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0.2V LINEAR LED DRIVER CONTROLLER
Application Information (Continued)
High voltage operation
The AL8400 also provides the capability to drive longer LED chains as the voltage across the LED chain is determined by the external switch. The lower supply voltage for the AL8400 can be derived from the supply to the LED chain either by putting a series resistor to the AL8400's VCC pin and putting a suitable zener diode from its VCC to GND Figure 5 or by tapping its VCC from the LED chain Figure 6.
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Figure 5. High voltage operation with zener diode from VIN
Figure 6. High voltage operation tapping VCC from the LED string
When the supply voltage for the AL8400 is derived using a zener diode, care has to be taken in dimensioning the resistor R1. The current spilled from VIN has to be enough to polarize the zener and to supply the LED driver. On the other hand, when the supply voltage for the AL8400 is derived from the LED string, care has to be taken in dimensioning the resistor RB. The current spilled from the LED chain can reduce the accuracy of the system and brightness matching between the LED.
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0.2V LINEAR LED DRIVER CONTROLLER
Ordering Information
Device AL8400SE-7
Notes: 2. 3.
Package Code SE
Packaging (Note 3) SOT353
7" Tape and Reel Quantity Part Number Suffix 3000/Tape & Reel -7
EU Directive 2002/95/EC (RoHS). All applicable RoHS exemptions applied. Please visit our website at http://www.diodes.com/products/lead_free.html Pad layout as shown on Diodes Inc. suggested pad layout document AP02001, which can be found on our website at http://www.diodes.com/datasheets/ap02001.pdf.
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Marking Information
(1) SOT353
( Top View )
5
4
7
XX Y W X 1 2 3
XX : Identification code Y : Year 0~9 W : Week : A~Z : 1~26 week; a~z : 27~52 week; z represents 52 and 53 week X : A~Z : Green
Package SOT353 Identification Code B4
Part Number AL8400SE-7
Package Outline Dimensions (All Dimensions in mm)
(1) Package Type: SOT353
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0.2V LINEAR LED DRIVER CONTROLLER
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