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ADT7110
General Description
The ADT7110 is a fixed frequency step-down converter designed to drive Infrared LEDs in the CCD camera module application. And internal current limit circuit protect external devices.
1 2 3 Package outline of the ADT7110 6 5 A11 4
Features
* 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
Applications
* Infrared LED driver for CCD camera
* Small outline SOT-26 package (2.9mm x 1.6mm body)
Typical Application Circuit
VOUT
RSE
RS
VIN C2
VIN
A11
GND RFB2 RFB1a L1 RFB1b C1 RFB1c RFB1d RFB1e RLED5 RLED6 RLED4 RLED3 RLED2 RLED1 RFB1f U1
EN
EN
FB
PWM
VFB
* This specifications are subject to be changed without notice
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ADT7110
Part List
Component U1*1 L1 C1 C2 RSE RLED1 ~ RLED6*2 Description Composite type with a PNP transistor and schottky barrier diode Output filter inductor Output filter capacitor Bypass capacitor Current sense resistor LED current ballast resistor Buck converter feedback loop component Buck converter feedback loop component IC Chip inductor Tantalum capacitor Tantalum capacitor Chip resistor Chip resistor , 1% Chip resistor Chip resistor , 1% Type FP103 47uH/590mA 47uF/16V 10uF/25V 0.1 4.0 120 (table 3) 68 (table 2) Value
RFB1a ~ RFB1f RFB2*3
*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 PNP Collector Current Schottky Barrier Diode Repetitive Peak Reverse Voltage Average Rectified Current -2 30 700 A V mA Parameter Collector to Emitter Voltage Ratings -23 Unit V Remarks Recommend `2SB1706' by ROHM or Equivalent IC Recommend `RSX101M-30' by ROHM or Equivalent
* This specifications are subject to be changed without notice
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ADT7110
Pin Configuration
1 6
A11
2
5
3
4
Pin Description
Pin No. 1 2 3 4 5 6 I : Input pin P : Power pin A : Analog pin Name RS GND PWM FB EN VIN I/O I O I I Type A G D A D P Description Current sense and provide voltage feed-forward. Ground Switching output. Feedback voltage input Device enable pin Power supply input
O : Output pin G : Ground pin D : Digital pin
IO : Input/Output pin
Functional Block Diagram
VIN EN Internal REG. Current Sense OSC Set Current Limit + GND REF + FB gm Error Amplifier PWM Comparator + Set Control Logic SW + RS
BIAS
Driver
* This specifications are subject to be changed without notice
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ADT7110
Absolute Maximum Ratings
Parameter Power supply voltage Power dissipation (Ta=70) (Note1) Storage temperature Junction temperature Thermal resistance Symbol VIN PDmax TSTG TJmax JA Min. -65 Typ. 301.2 Max. 23 265 +150 +150 Unit V /W
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 Power supply voltage*2 Operating temperature Junction temperature Max. power dissipation (Ta=70)*1 Symbol VIN TOPR TJ PD Min. 10.5 -20 Typ. 12.0 Max. 15.0 +85 +125 180 Unit V
*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) Drive current () 16 330 17 310 18 290 19 270 20 250 21 230 22 210
Electrical Characteristics (Ta=25, VIN=12V, unless otherwise noted)
Parameter Supply current, operating Supply current, disable V(EN), input voltage high V(EN), input voltage low PWM controller Output drive current Current limit Efficiency Oscillator frequency Feedback voltage (VFB) VIN 15V IO=300 IO=300 550 350 300 85 500 350 625 2.26 Condition V(EN) = 3.3V , IO=300 V(EN) = 0V MIN 2.4 TYP 6 90 MAX 9 200 1.2 Unit Note
V V

% V
IO=300 2.21 * This specifications are subject to be changed2.16 without notice
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ADT7110
Typical Performance Characteristics
LED current vs. Ta
LED current (mA) 53
Freq (kHz) 510
Switching frequency vs. Ta
52
505
51
500
50
495
49
48 30 40 50 60 70 80 90
490 30 40 50 60 70 80 90
Ambient temperature ()
Ambient temperature ()
Efficiency vs. Load current
Efficiency (%) 90% VIN=12V VIN=15V
85%
80%
75% 100 150 200 250 Load current (mA) 300 350 400
* This specifications are subject to be changed without notice
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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 () 5.76 4.42 4.02 2.67 2.49 LED current (mA) 35 45 50 75 80
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.
R FB1 20 k x number of LED branches
Typical application circuit shows 6 LED 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 6 5 4 3 2 1 RFB1 (k) 120 100 80 60 40 20
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
RFB2 (k) 61.9 64.9 66.5 68.1 69.8 71.5 73.2 75.0 VLED (V) 8.4 8.6 8.8 9.0 9.2 9.4 9.6 9.8
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
(+) (-)
Voltage meter
R FB 2
VLED - V FB 100uA
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 x efficiency x IN x , where VOUT N
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
N : the number of LED branch efficiency : efficiency of the ADT7110 at applied condition

* This specifications are subject to be changed without notice
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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

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