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CONSONANCE
Low-Dropout High-Power LED Driver
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CN5611
General Description:
The CN5611 current regulator operates from a 2.7V to 6V input voltage range and delivers a constant current that is up to 800mA to high-brightness LEDs, including high-brightness white LED. The LED current of CN5611 can be adjusted from 30mA to 800mA by using an external resistor. An on-chip pass element minimizes external components while providing 8% output current accuracy. Additional features include over temperature protection, LED short and open protection. The CN5611 is available in a thermally enhanced 5-pin SOT89 package.
Features:
Operating Supply Voltage Range: 2.7V to 6V On-chip Pass Element Low-Dropout Voltage Adjustable Output Current up to 800mA Output Current Accuracy: 8% Over Temperature Protection LED Open/Short Protection Operating Temperature Range: 40 to 85 Available in 5-pin SOT89 Packages Pb-free
Pin Assignment
VDD 1 GND 2 LED 3
5
Applications:
High-Power LED Driver LED Cap-Lamp Flash Light and Lighting Cell Phone, DSC and MP3 Player LCD and Keyboard Backlight
NC
CN5611
4
ISET
Typical Application Circuit
Input Supply Voltage 2.7V to 6V VDD LED RISET
CN5611
ISET GND LED
Figure 1 Typical Application Circuit
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Block Diagram
VDD
ISET
LED +
Bandgap Reference
Current Mirror
GND
Figure 2 Block Diagram Pin Description
Pin No. 1 2 3 Name VDD GND LED Function Description Positive Supply Voltage. VDD is the power supply to the internal circuit. Ground Terminal. LED Cathode Connection Pin. Constant LED Current Setting Pin. The constant LED current is set by connecting a resistor RISET from this pin to VDD. The LED current is determined by the following equation: Iout = 910VRISET Where, Iout is in ampere(A) RISET is in ohm() No Connection.
4
ISET
5
NC
Absolute Maximum Ratings
All Terminal Voltage...............0.3V to 6.5V Operating Temperature...............40 to 85 Thermal Resistance(Junction to Case) .....32/W Maximum Junction Temperature......150 Storage Temperature..................65 to 150 Lead Temperature(Soldering)...........300
Stresses 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 above 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.
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Electrical Characteristics
(VIN=3.7V, TA=25, unless otherwise noted) Parameters Input Supply Voltage Operating Current LED Pin Sink Current LED Current Tolerance Over Temperature Protection Temperature Over Temperature Protection Hysteresis LED pin Leakage Current TOTP TH ILKG VDD=GND, VLED=5.5V ILED=100mAx90% ILED=200mAx90% LED Dropout Voltage VDROP ILED=300mAx90% ILED=500mAx90% ILED=700mAx90% Thermal Resistance Thermal Resistance JC JA Junction to Case Junction to Ambient, No heat sink, No air flow 95 135 175 280 410 32 135 /W /W mV Symbol VDD IVDD ILED RISET=10K ohm RISET=3K 279 8 125 11 1 Test Conditions Min 2.7 335 303 327 8 Typ Max 6 Unit V uA mA % uA
Detailed Description
The CN5611 is a current regulator capable of providing LED current up to 800mA to high-power LEDs. In addition, CN5611 features over temperature protection, LED open/short protection. The CN5611 enters a thermal-shutdown mode in the event of over temperature. This typically occurs in overload or LED short-circuit conditions. When CN5611's junction temperature exceeds TJ = 125 (typical), the current flowing into LED pin is about 1% of that set by RISET to prevent the device from damage. CN5611 recovers from thermal-shutdown mode once the junction temperature drops by 11C (typical). The device will therefore protect itself by thermally cycling in the event of LED short-circuit or overload condition.
Application Information
Adjusting LED Current
CN5611 uses a resistor between ISET pin and VDD pin to set the LED current. The LED current is given by the following equation: ILED = 910V / RISET Where: ILED is the LED current in ampere(A) RISET is the resistance from the ISET pin to VDD pin in ohm() For best stability over temperature and time, 1% and 1/10W metal film resistors are recommended.
Thermal Consideration
The CN5611's maximum allowable power dissipation is given by the following equation: PDmax(TJTA)/J Where PDmax is the maximum allowable power dissipation TJ is the maximum junction temperature of CN5611, TJ=125 due to the
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effect of over temperature protection circuit TA is the CN5611's ambient temperature JA is the thermal resistance of CN5611, when there is no heat sink and no air flow, JA is 135/W, and it will be decreased to a great extent when there is heat sink, So in order to maximize LED current, careful thermal consideration must be given when designing PCB. The actual power dissipation of CN5611 is given by the following equation: PDactVLEDxILED where PDact is CN5611's actual power dissipation VLED is the maximum voltage at LED pin ILED is the designed output current For the purpose of normal operation for CN5611, PDact must be less than PDmax.
Drive Multi-LEDs
When multi-LEDs are needed to be driven, the circuit in Figure 3 or in Figure 4 can be used. VIN is the high input supply voltage that is used to drive multi-LEDs, CN5611's operating voltage can be from an independent source as shown in figure 3, or generated from VIN as shown in figure 4.
VIN LED VDD(2.7V to 6V) LED VDD RISET LED
CN5611
ISET GND LED
Figure 3 Drive Multi-LEDs from 2 Voltage Sources
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VIN
LED R1
LED VDD RISET LED
CN5611
D1 ISET GND LED
Figure 4 Drive Multi-LEDs from a High Voltage Sources
In the circuit of Figure 3 and Figure 4, care must be taken to make sure that the voltage at CN5611's LED pin should be kept less than 6V under any conditions. In the circuit of Figure 4, D1 is the zener diode whose breakdown voltage is between 2.7V to 6V. R1's resistance should be small enough so that the current flowing through R1 is greater than 3mA under worst case. For more application circuits, please refer to "CN5611-CN5612 Application Circuit Collection".
Dimming Control
There are 3 different ways of dimming control: 1. Using a PWM signal for dimming control as shown in Figure 5
VDD(2.7V to 6V)
VDD RISET
CN5611
ISET PWM Signal GND M1 LED
Figure 5
Dimming Control by Using PWM Signal
With PWM signal applied to the gate of N channel MOSFET M1, the LEDs operate at either zero or full current. The average LED current decreases with the increasing duty cycle of PWM signal. A 100% duty cycle will turn off LEDs completely, a 0% duty cycle corresponds to full LED current. The frequency of PWM signal should be under 10KHz.
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2. Using a logic signal for dimming control as shown in Figure 6 For applications that need to adjust the LED current in discrete steps, a logic signal can be used as shown in Figure 6. RISET1 sets the minimum LED current (when the PMOS is off, namely logic signal is high). RISET2 sets how much the LED current increases when the PMOS is turned on(logic signal is logic low).
VDD(2.7V to 6V)
Logic Signal
M1 RISET1
VDD
CN5611
RISET2 ISET GND LED
Figure 6
Dimming Control by Using Logic Signal
3. Using a variable resistor for dimming control as shown in Figure 7
VDD(2.7V to 6V)
RISET2 VDD
RISET1 ISET
CN5611
LED GND
Figure 7 Dimming Control by Using Variable Resistor
Board Layout Considerations
It is very important to use a good thermal PC board layout to maximize LED current. The thermal path for the heat generated by the IC is from the die to the copper lead frame through the package lead(especially the LED and ground lead) to the PC board copper, the PC board copper is the heat sink. The footprint copper pads should be as wide as possible and expand out to larger copper areas to spread and dissipate the heat to the surrounding ambient. Feedthrough vias to inner or backside copper layers are also useful in improving the overall thermal performance of CN5611. Other heat sources on the board, not related to CN5611, must also be considered when designing a PC board layout because they will affect overall temperature rise and the maximum LED current.
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The ability to deliver maximum LED current under all conditions require that the exposed metal pad on the back side of the CN5611 package be soldered to the PC board ground. Failure to make the thermal contact between the exposed pad on the backside of the package and the copper board will result in larger thermal resistance.
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Package Information
Consonance does not assume any responsibility for use of any circuitry described. Consonance reserves the right to change the circuitry and specifications without notice at any time.
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