ADT7110 General Description 6 The ADT7110 is a fixed frequency step-down 4 5 converter designed to drive Infrared LEDs in the A11 CCD camera module application. 1 And internal current limit circuit protect external devices. 3 2 Package outline of the ADT7110 Applications Features • Infrared LED driver for CCD camera • Input voltage range : 10.5V to 15V • Current mode PWM controller with integrated compensation components • 350mA output load current available • Built-in chip enable/disable function • Built-in current limit protection • 500kHz fixed frequency internal oscillator • Small outline SOT-26 package (2.9mm x 1.6mm body) Typical Application Circuit VOUT RSE RS VIN VIN C2 RFB2 A11 GND PWM RFB1a EN EN FB U1 L1 RFB1b C1 RFB1c RFB1d RFB1e VFB RLED6 RLED5 RLED4 RLED3 RLED2 RLED1 RFB1f * This specifications are subject to be changed without notice Jun. 07. 2008 / Rev. 0.1 1/8 http://www.ad-tech.co.kr ADT7110 Part List Component Description U1*1 Composite type with a PNP transistor and schottky barrier diode IC FP103 L1 Output filter inductor Chip inductor 47uH/590mA C1 Output filter capacitor Tantalum capacitor 47uF/16V C2 Bypass capacitor Tantalum capacitor 10uF/25V RSE Current sense resistor Chip resistor 0.1Ω LED current ballast resistor Chip resistor , 1% 4.0Ω RFB1a ~ RFB1f Buck converter feedback loop component Chip resistor 120㏀ (table 3) RFB2*3 Buck converter feedback loop component Chip resistor , 1% 68㏀ (table 2) RLED1 ~ RLED6*2 Type Value *1 : For cost down , it is possible to use discrete component with a PNP transistor and a schottky barrier diode. In this case, you make use the discrete components with proper electrical specification. Table A shows the required key electrical limits. It is recommended to use PNP and schottky barrier diode having equivalent specification in the Table A. *2, *3 : To setting appropriate LED current, Refer to ‘Application Hints’. Table A : Selection guide for the discrete components Component Parameter Ratings Unit Collector to Emitter Voltage -23 V Collector Current -2 A Repetitive Peak Reverse Voltage 30 V Average Rectified Current 700 mA PNP Schottky Barrier Diode Remarks Recommend ‘2SB1706’ by ROHM or Equivalent IC Recommend ‘RSX101M-30’ by ROHM or Equivalent * This specifications are subject to be changed without notice Jun. 07. 2008 / Rev. 0.1 2/8 http://www.ad-tech.co.kr ADT7110 Pin Configuration 1 6 A11 2 5 3 4 Pin Description Pin No. Name I/O Type 1 RS I A Current sense and provide voltage feed-forward. 2 GND - G Ground 3 PWM O D Switching output. 4 FB I A Feedback voltage input 5 EN I D Device enable pin 6 VIN - P Power supply input I : Input pin P : Power pin A : Analog pin O : Output pin G : Ground pin D : Digital pin Description IO : Input/Output pin Functional Block Diagram VIN EN Current Sense Internal REG. OSC ∑ + RS Set BIAS Current Limit + PWM Comparator Error Amplifier GND REF + FB Driver Control Logic + gm SW Set - * This specifications are subject to be changed without notice Jun. 07. 2008 / Rev. 0.1 3/8 http://www.ad-tech.co.kr ADT7110 Absolute Maximum Ratings Parameter Symbol Min. Typ. Max. Unit VIN - - 23 V Power dissipation (Ta=70℃) (Note1) PDmax - - 265 ㎽ Storage temperature TSTG -65 - +150 ℃ Junction temperature TJmax - - +150 ℃ Thermal resistance ΘJA - 301.2 - ℃/W Power supply voltage Note1. derate 301℃/W above +70℃. 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 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. Operating Ratings Parameter Symbol Min. Typ. Max. Unit Power supply voltage*2 VIN 10.5 12.0 15.0 V Operating temperature TOPR -20 - +85 ℃ Junction temperature TJ - - +125 ℃ Max. power dissipation (Ta=70℃)*1 PD - - 180 ㎽ *1 This spec. indicates that junction temperature of the device is under 125℃. In specific applications , this is recommended under this power dissipation specification. *2 Minimum VIN operating range is dependant to the VOUT voltage. ( VIN min. ≒ VOUT + 0.5V) Maximum VIN operating range can be extended. In this case, maximum drive current is limited. For using VIN over 15V, refer to the Table B. Table B : Maximum drive current as maximum VIN operating voltage. VIN (V) 16 17 18 19 20 21 22 Drive current (㎃) 330 310 290 270 250 230 210 Electrical Characteristics (Ta=25℃, VIN=12V, unless otherwise noted) Parameter Condition MIN TYP MAX Unit Supply current, operating V(EN) = 3.3V , IO=300㎃ - 6 9 ㎃ Supply current, disable V(EN) = 0V - 90 200 ㎂ V(EN), input voltage high - 2.4 - - V V(EN), input voltage low - - - 1.2 V Output drive current VIN ≤ 15V - 300 350 ㎃ Current limit - 550 - - ㎃ Efficiency IO=300㎃ - 85 - % Oscillator frequency IO=300㎃ 350 500 625 ㎑ 2.26 V Note PWM controller Feedback voltage (VFB) Jun. 07. 2008 / Rev. 0.1 IO=300㎃ 2.21 * This specifications are subject to be changed2.16 without notice 4/8 http://www.ad-tech.co.kr ADT7110 Typical Performance Characteristics LED current vs. Ta Switching frequency vs. Ta LED current (mA) 53 Freq (kHz) 510 52 505 51 500 50 495 49 48 490 30 40 50 60 70 80 90 Ambient temperature (℃) 30 40 50 60 70 80 90 Ambient temperature (℃) Efficiency vs. Load current Efficiency (%) 90% VIN=12V VIN=15V 85% 80% 75% 100 150 200 250 300 350 400 Load current (mA) * This specifications are subject to be changed without notice Jun. 07. 2008 / Rev. 0.1 5/8 http://www.ad-tech.co.kr ADT7110 Application Hints ▶ LED Current control The LED current is determined by current ballast resistor (RLED1~RLED6) and feedback resistor (RFB2). The current setting procedure is described as below. i) Choose the RLED1 ~ RLED6 The voltage on current ballast resistor (RLED) is about 200mV normally. So the LED current is 200mV/RLED. In order to set LED current accurately, the precision resistors are preferred (1% recommended). The RLED value as LED current is shown as below table. < table 1 > RLED vs. LED current RLED (Ω) LED current (mA) 5.76 35 4.42 45 4.02 50 2.67 75 2.49 80 ii) Choose the RFB2 Secondly you choose appropriate RFB2 value for setting VLED. RFB2 is determined by forward voltage of the 6 series LEDs because the forward voltages of LED are different each other according to the LED manufacturers. (1.2 ~ 1.5volts for VF setting current flow away). The table and formula of the RFB2 are shown as below. < table 2 > RFB2 vs. VLED VLED (V) 61.9 8.4 64.9 8.6 66.5 8.8 68.1 9.0 69.8 9.2 71.5 9.4 73.2 9.6 75.0 9.8 R FB1 ≈ 20circuit k Ω × number LED branches Typical application shows 6 ofLED branches and each LED branch has 6 series LEDs. In this circuit, proper RFB1 value is 120㏀ and RFB1a ~ RFB1f value are used 120㏀ equally. The RFB1 value by the number of LED branch is shown below. < table 3 > RFB1 by the LED branches Number of LED branch RFB1 (kΩ) 6 120 5 100 4 80 3 60 2 40 1 20 ▶ LED current check The accurate method of measuring LED current is to measure the voltage on current ballast resistor (RLED). And then the LED current is simply obtained by dividing this voltage by RLED. To measure voltage on RLED accurately, (-) probe of the voltage meter is connected to (-) terminal of the ballast resistor and measure the voltage of (+) terminal on ballast resistor. Fig. 2 shows the method of measuring voltage on ballast resistor. LED current= V(RLED1)/RLED1 (+) (-) V(RLED1) RLED1 R FB 2 ≈ RFB2 (kΩ) iii) Choose the RFB1 (= RFB1a ~ RFB1f ) RFB1 is used to biasing of LED. And these resistor value should be changed by the number of the LED branch. Therefore you should choose appropriate RFB1 value according to the LED branch count. The RFB1 selection formula is shown as below. VLED − V FB 100uA Voltage meter <Fig. 2 LED current test> Where the VLED is the sum of the forward voltage in 6 series LEDs at setting current and VFB is the feedback voltage. (typically 2.21V) Fig. 1 shows the method of measuring VLED. VLED Setting current It is possible to calculate the LED current by measuring of ICC current. As the ADT7110 is basically buck converter, its ICC current is the function of VIN, VOUT, LED branch current and quiescent current. Therefore it is not easy to calculate accurate LED current by measurement of ICC current. The relation LED branch current to the ICC current is shown below formula. V 1 I LED .1branch ≈ ICC × efficiency × IN × , where VOUT N N : the number of LED branch efficiency : efficiency of the ADT7110 at applied condition <Fig. 1 VLED test> * This specifications are subject to be changed without notice Jun. 07. 2008 / Rev. 0.1 6/8 http://www.ad-tech.co.kr ADT7110 Application Hints (continued) Example : typical application circuit N = 6 (6 LED branches) VIN = 12V , VOUT = 9V ICC = 280mA (measured) , and efficiency is 80%. So, calculated 1 branch LED current is 49.77mA. ▶ Dimming control The LED brightness control can be obtained by forcing a pulse wave to the EN input terminal. Typically, a 100Hz to 1kHz pulse signal is used. LED brightness is proportional to the duty of pulse wave. And in this case , LED branch current is RMS value of the PWM modulated current. When the pulse-width is below 50% duty, the driving current of ADT7110 can be increased up to current limit condition.(~550mA) But you keep carefully to select the inductor (L1) over 700mA rated current. Note that the inductor (L1) is 590mA rated in typical application circuit. * This specifications are subject to be changed without notice Jun. 07. 2008 / Rev. 0.1 7/8 http://www.ad-tech.co.kr ADT7110 Package ; SOT-26, 2.9mm x 1.6mm body (units : mm) * This specifications are subject to be changed without notice Jun. 07. 2008 / Rev. 0.1 8/8 http://www.ad-tech.co.kr