STMicroelectronics LED7707 Application Note Download | Manualshive

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Revision history

AN2810

16/17

Doc ID 14893 Rev 1

10 Revision

history

Table 5.

Document revision history

Date

Revision

Changes

26-May-2009

1

Initial release

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Summary of Contents for LED7707

Page 1: ...ed in the backlighting of LCD panels The device can manage an output voltage up to 36 V i e ten white LEDs per row The generators can be externally programmed to sink up to 85 mA and can be dimmed via a PWM signal 1 of minimum dimming duty cycle at 1 kHz can be managed The device allows detection and management of open and shorted LED faults and permits unused rows to be left floating Basic protec...

Page 2: ...sembly and layout 7 5 I O interface 8 6 Recommended equipment 8 7 Configuration 8 7 1 SW1 fixed or adjustable switching frequency FSW pin 8 7 2 SW2 fault management mode MODE pin 9 7 3 SW3 enable function 10 8 Test setup 11 9 Getting started 12 9 1 Quick startup 12 9 2 Open and shorted WLEDs fault testing 13 9 3 Device synchronization 13 9 4 Efficiency measurements 14 10 Revision history 16 ...

Page 3: ... FSW setting 9 Figure 6 SW2 MODE setting 9 Figure 7 LED7707 demonstration board and white LED test board assembly 11 Figure 8 LED7707 demonstration board test setup 11 Figure 9 LED7707 synchronization setup 14 Figure 10 Efficiency measurement setup 15 Figure 11 Efficiency vs DIM duty cycle VIN 12 V 6 rows 10 white LEDs in series IOUT 360 mA 15 Figure 12 Efficiency vs DIM duty cycle VIN 24 V 6 rows...

Page 4: ...equency External sync for multi device application Pulse skip power saving mode at light load Programmable soft start Programmable OVP overvoltage protection Single ceramic output capacitor Non latched thermal shutdown 1 2 Backlight driver section Six rows with 85 mA maximum current capability adjustable Up to 10 WLEDs per row Parallelable rows for higher current Row disable option Less than 10 µs...

Page 5: ...ematic Table 1 LED7707 performance summary Parameter Conditions Value Minimum input voltage 6 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 360 kΩ 3 3 A Boost section switching frequency FSW pin to AVCC 660 kHz FSW pin to R5 330 kΩ 825 kHz Minimum dimming on time 400 Hz FDIM 20 kHz 10 µs Output current each row R6 24...

Page 6: ...d N M 1 C13 Ceramic 25 V X5R 20 SMD 0603 Standard N M 1 R1 Chip resistor 0 1 W 1 SMD 0603 Standard 510 kΩ 1 R2 Chip resistor 0 1 W 1 SMD 0603 Standard 16 kΩ 1 R3 Chip resistor 0 1 W 1 SMD 0603 Standard 2 4 kΩ 1 R4 Chip resistor 0 1 W 1 SMD 0603 Standard 4 7 Ω 1 R5 Chip resistor 0 1 W 1 SMD 0603 Standard 330 Ω 1 R6 Chip resistor 0 1 W 1 SMD 0603 Standard 24 kΩ 1 R7 Chip resistor 0 1 W 1 SMD 0603 St...

Page 7: ...ut Figure 3 Top side component placement Figure 4 Bottom side test points Qty Componen t Description Package Part number MFR Value 1 J8 Header 8 SIL 8 Standard 1 SW1 SW2 Jumper 3 SIL 3 Standard 1 SW3 Pushbutton 6x6mm FSM4JSMAT TYCO Table 2 LED7706 demonstration board component list continued ...

Page 8: ...r its status if this option is not required the monitor LED can be disconnected 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 250 kHz to 1 MHz see Figure 5 When placed in the down position the fixed switching frequency is selected Tabl...

Page 9: ...nnected to ground and the corresponding fault management is summarized in the first column of Table 4 Otherwise when SW2 is set to the down 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 FSW 2 5 R5 IXED 3WITCHING REQUENCY DEFAULT POSITION DJUSTABLE 3WITCHING FREQUENCY IXED 3WITCHING REQUENCY ...

Page 10: ...tivated whenever a new startup is required or to escape a latched condition Table 4 Fault management summary Fault MODE to GND MODE to VCC Internal MOSFET overcurrent Fault pin HIGH Power MOSFET turned off Output overvoltage FAULT pin LOW Power MOSFET turned off hysteretic regulation Thermal shutdown FAULT pin LOW Device turned off Automatic restart after 30 C temperature drop LED short circuit Fa...

Page 11: ...mpers and test points which can be used to easily perform functional testing of the LED7707 Figure 7 LED7707 demonstration board and white LED test board assembly Figure 8 shows the complete test setup Figure 8 LED7707 demonstration board test setup PWM Generator 6V 32V 2A Power Supply VBOOST VIN VIN GND DIM A Meter CH2 CH1 Scope V Meter ROW1 6x10 75mA WLEDs ARRAY PWM Generator 6V 32V 2A Power Sup...

Page 12: ...s of the LED7707 board 4 Set the PWM signal 500 Hz 5 duty cycle 3 3 V CMOS logic levels on a signal generator and connect it to the DIM input 5 Set SW1 and SW2 in the down position fixed frequency and MODE to AVCC Do not change jumpers settings when the board is powered 6 Set the input voltage to 12 V 7 Turn on the PWM generator 8 Turn on the VIN supply The device turns on 9 Vary the input voltage...

Page 13: ...n on the power supply and repeat steps 5 through 8 11 Remove all shorted WLEDs and leave ROW1 and ROW2 floating 12 Turn on the power supply The floating rows are ignored 13 Turn off the PWM generator 14 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 700 kHz clock ...

Page 14: ...lculated as follows Equation 2 where VSTRING_i is the voltage across the LEDs in row i whereas ISTRING_i is the current flowing through the row i To facilitate the measurement the voltage drop of all the generators is equalized by connecting them together In this condition the power provided to the LEDs is simple to calculate Equation 3 where VSTRING is the voltage across the parallelized channels...

Page 15: ...mming signal at two different input voltages Figure 11 Efficiency vs DIM duty cycle VIN 12 V 6 rows 10 white LEDsinseries IOUT 360mA Figure 12 Efficiency vs DIM duty cycle VIN 24 V 6 rows 10 white LEDs in series IOUT 360 mA PWM Generator 4 5V 32V 2A Power Supply 10 WLEDs 700mA array VBOOST VIN VIN GND DIM A Meter V Meter ROW1 V Meter A Meter PWM Generator 4 5V 32V 2A Power Supply 10 WLEDs 700mA ar...

Page 16: ...Revision history AN2810 16 17 Doc ID 14893 Rev 1 10 Revision history Table 5 Document revision history Date Revision Changes 26 May 2009 1 Initial release ...

Page 17: ...WARRANTIES OF MERCHANTABILITY FITNESS FOR A PARTICULAR PURPOSE AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION OR INFRINGEMENT OF ANY PATENT COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT UNLESS EXPRESSLY APPROVED IN WRITING BY AN AUTHORIZED ST REPRESENTATIVE ST PRODUCTS ARE NOT RECOMMENDED AUTHORIZED OR WARRANTED FOR USE IN MILITARY AIR CRAFT SPACE LIFE SAVING OR LIFE SUSTAINING APPLICAT...

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