AN2809 Application note 6-row / 30-mA LED driver with boost converter for the backlight of LCD panels Introduction The LED7706 consists of a high-efficiency monolithic boost converter and six controlled current generators (rows) specifically designed to supply the LED arrays used in the backlights of LCD panels. The device can manage an output voltage of up to 36 V (ten white LEDs per row). The generators can be externally-programmed to sink up to 30 mA and can be dimmed via a PWM signal (a 1% dimming duty-cycle at 20 kHz can be managed). The device detects and manages the open and shorted LED faults and leaves unused rows floating. Basic protections (output over-voltage, internal MOSFET over-current and thermal shutdown) are provided. Figure 1. February 2009 LED7706 demonstration board Rev 2 1/22 www.st.com Contents AN2809 Contents 1 LED7706 main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1 Boost section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2 Backlight driver section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 LED7706 demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4 Components assembly and layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5 I/O interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6 Recomended equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 7 Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.1 SW1 fixed or adjustable switching frequency (FSW pin) . . . . . . . . . . . . . 10 7.2 SW2 fault management mode (MODE pin) . . . . . . . . . . . . . . . . . . . . . . . 11 7.3 SW3 enable function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 8 Test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 9 Getting started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 9.1 Quick startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 9.2 Open and shorted WLEDs fault testing . . . . . . . . . . . . . . . . . . . . . . . . . . 14 9.3 Device synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 9.4 Efficiency measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 10 WLEDs test board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 11 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2/22 AN2809 List of figures List of figures Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. LED7706 demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 LED7706 board schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Top side component placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Bottom side test points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 SW1 (FSW) setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 SW2 (MODE) setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 LED7706 demonstration board and white LEDs test board assembly . . . . . . . . . . . . . . . . 12 LED7706 board test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 LED7706 synchronization setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Efficiency measurements setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Efficiency vs DIM duty cycle, VIN=12V, 10 white LEDs in series, IOUT = 120mA . . . . . . . . 17 Efficiency vs DIM duty cycle, VIN=24V, 10 white LEDs in series, IOUT = 120mA . . . . . . . . 17 WLEDs test board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 WLEDs test board schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3/22 List of tables AN2809 List of tables Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. 4/22 LED7706 performance summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 LED7706 component list. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 LED7706 demonstration board test points description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Faults management summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Test board jumpers function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Test boards switches functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Test board test-points function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 AN2809 LED7706 - main features 1 LED7706 - main features 1.1 Boost section 1.2 ● 4.5- to 36-V input voltage range ● Internal power MOSFET ● Internal +5 V LDO for device supply ● Up to 36-V output voltage ● Constant frequency peak current-mode control ● 200-kHz to 1-MHz adjustable switching frequency ● External sync for multi-device application ● Pulse-skip power-saving mode at light loads ● Programmable soft-start ● Programmable OVP protection ● Single ceramic output capacitor ● Non-latched thermal shutdown Backlight driver section ● Six rows with 30 mA maximum current capability (adjustable) ● Up to 10 white LEDs per row ● Row disabling option ● Less than 500 ns minimum dimming time (1% minimum dimming duty-cycle at 20 kHz dimming frequency) ● ±2.0% current matching between rows ● LED failure (open and short circuit) detection 5/22 LED7706 demonstration board 2 AN2809 LED7706 demonstration board The LED7706 demonstration board has been designed to manage six strings of 8 to 10 white LEDs each. Table 1 summarizes the board features and Figure 2 shows the schematic of the LED7706 demonstration board. The input voltage range is limited to 32 V because of the 35 V rated input capacitor. Extended operating input voltage ranges (up to 36 V) can be achieved by using a 50-V rated MLCC. Table 1. LED7706 performance summary Parameter Conditions Value Minimum input voltage 4.5 V Maximum input voltage 32 V Output voltage VIN<VBOOST<36 V Output OVP threshold R1 = 510 kΩ, R2 = 16 kΩ 38 V Internal MOSFET OCP R7 = 180 kΩ 3.3 A FSW pin to AVCC 660 kHz FSW pin to R5 = 330 kΩ 825 kHz 400 Hz < FDIM < 20 kHz 500 ns Boost section switching frequency Minimum dimming on-time 19.6 mA Output current (each row) R6=51 kΩ Output current accuracy ±2.0% VIN = 12 V, VBOOST = 34 V, FSW = 660 kHz Efficiency Figure 2. 91% LED7706 board schematic $ 6). , U 3403,- # U 6). 2 K 2 K 39 .# * !6## !6## 3,/0% 2 K 2%$ M! # N !6## /63%, 2 2 &!5,4 #/-0 # N %. # .- N $)-/$% #/-0 33 33 # # !6## &37 N 2 K 2/7 2/7 2/7 2/7 2/7 2/7 4(0$ 2 K # U # .- 6"//34 37 '.$ * (%!$%2 3'.$ !6## %. "),)- $)- 2 K # U # P ,%$ 0'.$ &!5,4 &37 %. 37 3,/0% ,$/ 2),)- 37 2 K U # /63%, ,8 $ 6). 5 ,%$?%. 39.# !6## 2 K 2),)- "),)- 2 K 2 K 2/7 2/7 2/7 2/7 2/7 2/7 6). !-V 6/22 AN2809 Component list 3 Component list Table 2. LED7706 component list Qty Component Description Package Part number MFR Value UMK325BJ106KM-T Taiyo Yuden 10µF GRM31CR71H475KA88B MURATA 1 C1 Ceramic, 35V, X5R, 20% SMD 1210 1 C2 Ceramic, 50V, X7R, 20% SMD 1206 4.7µF 2 C3, C4 Ceramic, 50V, X7R, 20% SMD 1206 N.M. 1 C5 Ceramic, 25V, X5R, 20% SMD 0603 Standard 1µF 1 C6 Ceramic, 25V, X5R, 20% SMD 0603 Standard 100nF 1 C7 Ceramic, 25V, X5R, 20% SMD 0603 Standard 3.3nF 1 C8 Ceramic, 25V, X5R, 20% SMD 0603 Standard 4.7nF 1 C9 Ceramic, 25V, X5R, 20% SMD 0603 Standard N.M. 1 C10 Ceramic, 25V, X5R, 20% SMD 0402 Standard 220pF 1 C11 Ceramic, 25V, X5R, 20% SMD 0603 Standard 4.7nF 1 R1 Chip resistor, 0.1W, 1% SMD 0603 Standard 510kΩ 1 R2 Chip resistor, 0.1W, 1% SMD 0603 Standard 16kΩ 1 R3 Chip resistor, 0.1W, 1% SMD 0603 Standard 2.4kΩ 1 R4 Chip resistor, 0.1W, 1% SMD 0603 Standard 4.7Ω 1 R5 Chip resistor, 0.1W, 1% SMD 0603 Standard 330kΩ 1 R6 Chip resistor, 0.1W, 1% SMD 0603 Standard 51kΩ 1 R7 Chip resistor, 0.1W, 1% SMD 0603 Standard 180kΩ 1 R8 Chip resistor, 0.1W, 1% SMD 0603 Standard 680kΩ 2 R9, R10 Chip resistor, 0.1W, 1% SMD 0603 Standard 100kΩ 1 R11 Chip resistor, 0.1W, 1% SMD 0603 Standard 1.2kΩ 1 L1 6µ8, 75mH, 2.7A 6x6mm LPS6235-682MLC Coilcraft 6.8µH 1 D1 Schottky, 40V, 1A DO216-AA STPS1L40M ST STPS1L40M 1 D2 Red LED, 3mA SMD 0603 1 U1 Integrated circuit QFN4x4 1 J2 PCB pad jumper 1 J8 Header 8 SIL 8 Standard 1 SW1, SW2 Jumper 3 SIL 3 Standard 1 SW3 Pushbutton 6x6mm Standard LED7706 FSM4JSMAT ST LED7706 TYCO 7/22 Component assembly and layout 4 8/22 Component assembly and layout Figure 3. Top side component placement Figure 4. Bottom side test points AN2809 AN2809 5 I/O interface I/O interface The LED7706 demonstration board has the following test points. Table 3. Description of LED7706 demonstration board test points Test point Description VIN+ Input voltage, positive terminal VIN- Input voltage, negative terminal GND Reference ground Row1 to row6 VBOOST Current generators output Boost regulator output voltage DIM PWM dimming input EN Enable input (active high) SYNC Synchronization output FSW Synchronization input FAULT Fault signal, active low 9/22 Recommended equipment 6 7 AN2809 Recommended equipment ● 4.5–32 V, 2 A capable power supply. ● Digital multimeters. ● 200 MHz oscilloscope. ● Signal generators for PWM dimming and synchronization clock (optional). Configuration The LED7706 demonstration board allows the user to select the desired mode of operation using the SW1 and SW2 selectors. Refer to the following configuration description. A red LED is connected to the FAULT pin to easily monitor its status; if this option is not desired, the monitor LED can be disconnected by opening the J2 jumper. 7.1 SW1 fixed or adjustable switching frequency (FSW pin) The SW1 selector is used to choose between the fixed switching frequency (660 kHz) and a user-defined switching frequency in the range of 200 kHz to 1 MHz. When connected in the lower position, the fixed switching frequency is selected. If SW1 is in the upper position, the switching frequency is given by: F SW = 2.5 ⋅ R 5 Figure 5. SW1 (FSW) setting !DJUSTABLE3WITCHINGFREQUENCY &IXED3WITCHING&REQUENCY DEFAULTPOSITION !-V The R5 resistor is set to 330 kΩ (FSW = 825 kHz). 7.2 SW2 fault management mode (MODE pin) The SW2 selector is used to connect the MODE to AVCC or ground. When the jumper is set to the upper position, the MODE pin is connected to ground and the corresponding fault management is summarized in the first column of Table 4. 10/22 AN2809 Configuration Otherwise, when SW2 is set to the lower position, the MODE pin is connected to AVCC and the corresponding fault management is summarized in the second column of Table 4. Figure 6. SW2 (MODE) setting 02'(SLQWRJURXQG VHH7DEOHVW FROXPQ 02'(SLQWR$9&& VHH7DEOHQG FROXPQ !-V Table 4. Fault management summary Fault 7.3 MODE to GND MODE to VCC Internal MOSFET over current Fault pin HIGH Power MOSFET turned OFF Output overvoltage FAULT pin LOW Device turned OFF, latched condition Thermal shutdown FAULT pin LOW. Device turned OFF. Automatic restart after 30°C temperature drop. LED short circuit Fault pin LOW Device turned OFF at first occurrence, latched condition (Vth=3.4V) Fault pin LOW Faulty row(s) disconnected. Device keeps on working with the remaining row(s) (Vth=6V) Open row(s) Fault pin LOW Device turned OFF at first occurrence, latched condition FAULT pin HIGH Faulty row(s) disconnected. Device keeps on working with the remaining row(s) SW3 enable function The terminals of the switch SW3 are connected on one side to the EN pin and on the other side to ground. Therefore, when the switch is not pressed, the EN pin is floating, which implies that the device is working. When the SW3 pin is pressed, the EN pin is connected to ground. When the SW3 is released, the device re-starts (the soft-start is performed). The SW3 switch can be activated whenever a new start-up is required or to escape a latched condition. 11/22 Test setup 8 AN2809 Test setup A proper WLED array is required as load to correctly evaluate the LED7706. Figure 7 shows a possible assembly of LED7706 with a WLEDs test board. This demonstration board includes 60 white LEDs (20 mA), switches, jumpers and test points used to easily perform the functional tests of the LED7706. Chapter 10 provides a brief description of the test board and its schematic, which can be used as reference for any customized board. Figure 7. LED7706 demonstration board and white LEDs test board assembly Figure 8 shows the complete test setup. Figure 8. LED7706 board test setup PWM Generator DIM GND + 4.5V – 32V @ 2A Power Supply VINA-Meter VIN+ ROW1 CH1 VBOOST V-Meter CH2 Scope 6x10 – 20mA WLEDs Test Board 12/22 AN2809 9 Getting started Getting started The following step-by-step sequences are provided as a guideline to quickly evaluate the performance of the LED7706 board. 9.1 Quick startup Note: Working in a ESD-protected environment is highly recommended. First check all wrist straps and mat earth connections before handling the LED7706 board. 1. Connect the power supply to the LED7706 board and insert the A-meter as shown in Figure 8. Connect a V-meter between VBOOST and ground to monitor the output voltage. 2. Connect the proper WLEDs array to the J8 connector or to the row1-row6 and VBOOST terminals of the LED7706 board. 3. Set the PWM signal (20 kHz, 5% duty-cycle, 3.3 V CMOS logic levels) on a signal generator and provide it to the DIM input. 4. Set SW1 and SW2 to the lower position (fixed frequency and MODE to AVCC). Do not change jumper settings when the board is switched on. 5. Set the input voltage to 12 V. 6. Turn on the PWM generator. 7. Turn on the VIN supply: the device turns on. 8. Vary the input voltage in the range 4.5–32 V. 9. Set the input voltage to 12 V. 10. Vary the dimming duty-cycle from 1 to 100%. 11. Check the shape of the rows’ current at a 1% dimming duty-cycle. Note: When measuring the current of row x, an auto-ranging A-meter can trigger the open-row or shorted-LED fault detection during the automatic scale selection procedure. Disabling the auto-ranging option on the A-meter is recommended. 13/22 Getting started 9.2 AN2809 Open and shorted WLED fault testing 1. Set the input voltage to 12 V. 2. Set the dimming duty-cycle to 20%. 3. Disconnect the rows in sequence and compare the behavior of the LED7706 to Table 4. 4. Restore all row connections and force the EN input to ground. 5. Release the EN input. 6. Short one or more WLEDs and compare the behavior of the LED7706 to Table 4. 7. Press the SW3 push button of the LED7706 board to reset the device. 8. Turn off the power supply and set the SW2 selector to the upper position (MODE to ground). 9. Turn on the power supply and repeat steps 3 to 7. 10. Remove all shorted WLEDs and leave ROW1 and ROW2 floating. 11. Turn on the power supply: the floating rows are ignored. 12. Turn off the PWM generator. 13. Turn off the power supply. 9.3 Device synchronization 1. Set the PWM dimming signal to 100%. 2. Remove the jumper from the SW1 selector to leave the FSW pin floating. 3. Connect an external 600 kHz clock generator (0 to 1 V logic levels, 40% duty-cycle) between the FSW test point and ground. Refer to Figure 9. 4. Turn on the PWM generator. 5. Turn on the power supply: the device remains off until the FSW pin is low. 6. Turn on the clock generator: the device turns on. 7. Monitor the SYNC output and verify the synchronization (the SYNC output is a replica of the FSW signal). 8. Turn off the PWM generator. 9. Turn off the clock generator. 10. Turn off the power supply. 14/22 AN2809 Getting started Figure 9. LED7706 synchronization setup 600kHz – 40% Clock Generator PWM Generator GND FSW SYNC DIM VIN4.5V – 32V @ 2A Power Supply VIN+ + VBOOST CH1 CH2 6x10 – 20mA WLEDs Test Board Scope 9.4 Efficiency measurements Figure 10 shows the set-up used to perform efficiency measurements. The efficiency in this device is typically defined as the ratio between the power provided to the load (current flowing through the LEDs multiplied by the voltage across the LEDs) and the total input power. The power dissipated in the current generators is correctly considered as a power loss. This method of calculating the efficiency implies that the voltage across the LEDs is the same for all the strings. However, this is not true. The power delivered to the load should be calculated as follows. 6 P LOAD = ∑ VSTRINGi ⋅ I STRINGi i=1 where VSTRING_i is the voltage across the LEDs in row i, whereas ISTRING_i is the current flowing through row i. In order to ease the measurement, the voltage drop of all the generators is equalized by connecting them together. 15/22 Getting started AN2809 In this condition, the power provided to the LEDs is simply calculated as: P LOAD = V STRING ⋅ I STRING where VSTRING is the voltage across the parallelized channels, whereas ISTRING is the total current delivered to the load (the sum of the current of the six channels). Since all the channels are in parallel (120 mA total current), a single string of 150 mA-rated LEDs is required as load (Figure 10). Figure 10. Efficiency measurement setup PWM Generator DIM GND + 4.5V – 32V @ 2A Power Supply VINA-Meter VIN+ ROW1 VBOOST V-Meter V-Meter A-Meter 10 WLEDs 150mA array Figure 11 and Figure 12 show two efficiency measurements against the duty-cycle of the dimming signal at two different input voltages. 16/22 AN2809 Getting started Figure 11. Efficiency vs DIM duty-cycle, Figure 12. Efficiency vs DIM duty-cycle, VIN = 12 V, 10 white LEDs in VIN = 24 V, 10 white LEDs in series, IOUT = 120 mA series, IOUT = 120 mA 17/22 WLEDs test board 10 AN2809 WLEDs test board The WLEDs test board here described mounts sixty vertical white LEDs (size 0603, 20 mA) arranged in a 6 x 10 matrix. Figure 13 shows an image of the board, whereas Figure 14 provides the schematic which can be used as reference to realize a customized board. Several jumpers, switches and test points are provided to cover most of the test configurations. Figure 13. WLEDs test board 18/22 2 2 2 2 2 1 1 1 1 1 D10 J19 D20 J23 D30 J27 D40 J31 D50 J35 D60 2 1 2 1 2 1 2 1 2 1 2 1 TP10 J10 J11 J12 J13 J14 2 1 J38 D9 J18 D19 J22 D29 J26 D39 J30 D49 J34 D59 TP9 1 2 1 2 1 2 1 2 1 2 1 2 1 1 1 TP21 1 1 1 1 1 1 J15 J39 TP19 TP20 1 J9 1 2 1 D8 J17 D18 J21 D28 J25 D38 J29 D48 J33 D58 J37 2 1 2 1 2 1 2 1 2 1 2 1 TP8 1 1 TP18 D7 J16 D17 J20 D27 J24 D37 J28 D47 J32 D57 J36 2 2 2 2 2 2 TP7 1 1 TP17 D6 D16 D26 D36 D46 D56 TP6 1 D5 D15 D25 D35 TP5 1 D4 D14 D24 D34 D44 TP4 1 1 D45 TP14 1 D54 TP15 1 D55 TP16 J1 D3 D13 D23 D33 D43 D53 J2 3 2 1 TP3 1 1 TP13 1 2 3 D2 D12 D22 D32 D42 D52 TP2 1 1 D1 D11 D21 D31 D41 D51 TP12 TP1 1 1 TP11 J3 J4 J5 J6 J7 1 2 1 2 1 2 1 2 1 2 SW1 SW2 SW DIP-6 SW3 J8 HEADER 8X2 8 7 6 5 4 3 2 1 AM00673v1 9 10 11 12 13 14 15 16 AN2809 WLEDs test board Figure 14. WLEDs test board schematic 19/22 WLEDs test board AN2809 Table 5, Table 6 and Table 7 respectively describe the board’s jumper functions, switches and test-points. Table 5. Test board jumper functions Jumper Function Default position J1 Two-position selector. Used in conjunction with SW1 to simulate a fault on shorted LEDs on row1. When set to position 1, the D10 LED can be shorted by pressing SW1. When set to position 2, both D9 and D10 LEDs can be shorted by pressing SW1. 1 J2 Two-position selector. Same function as J1 but related to row6 (D59 and D60 LEDs). 1 PCB tin-drop jumpers, bottom-sided. Used to parallelize the desired number of rows. J3 to J7 J8 8-terminal connector. Used to interface the LED7706 demonstration board. J9 PCB tin-drop jumper, bottom-sided. Used to provide the output voltage of the boost section of LED7706 to the low-current (D1D60), top-sided WLEDs array. Shorted J10 to J15 Two-pin jumpers, top-sided. Used to access the LED strings to perform row current monitoring and voltage threshold measurement. Shorted J16 to J39 PCB tin-drop jumper, bottom-sided. Used to reduce the number of active LEDs of each row by shorting unused diodes. Open Table 6. - Test board switch functions Switch Function Default position SW1 Used in conjunction with J1 to simulate a shorted LED fault condition. See J1 function. Open (released) SW2 Used in conjunction with J2 to simulate a shorted LED fault condition. See J2 function. Open (released) SW3 DIP switch. Used to individually break ROW1 through row6. Used to simulate open LED fault or unused (floating) rows. ON Table 7. Test board test-point functions Test point Function TP1 to TP10 PCB test points, top-sided. Used to easily access each LED of ROW1 (D1-D10). TP11 to TP20 PCB test points, top-sided. Used to easily access each LED of ROW6 (D51-D60). TP21 20/22 Open PCB test point, top-sided. Auxiliary access to the output voltage. AN2809 11 Revision history Revision history Table 8. Document revision history Date Revision Changes 10-Jan-2009 1 Initial release. 11-Feb-2009 2 Updated Table 2: LED7706 component list and Table 4: Fault management summary 21/22 AN2809 Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no liability whatsoever relating to the choice, selection or use of the ST products and services described herein. No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. 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