UM0677 STMICROELECTRONICS | Alldatasheet
Document overview
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- PDF pages: 16
Technical content
Datasheet sections
- 1 Introduction
- 2 Description of reference design
- 2.1 Current sensing
- 2.2 Dimming interface
- 3 Application
- 3.1 Measurement results
- 4 Bill of material
- 5 References and related materials
- 6 Revision history
1 Introduction
Figure 1. STEVAL-ILL023V1 - 2.8 A LED driver (LED is not included in the kit)
2 Description of reference design
border conditions as the current limit is defined only by the selection of the MOSFET. Table 1. Board parameters
- PWM signal has inverted characteristics (0% = full power).
Figure 2. 2.8 A LED driver based on the L6726A + external MOSFET
2.1 Current sensing
voltage reference TS821 is used, the losses are almost three times lower. header P1 as indicated in Ta ble 2. Figure 3. Part of schematics with highlighted components for efficient current Table 2. Nominal output current settings
Description of reference design UM0677 8/16 Doc ID 15396 Rev 2
2.2 Dimming interface
For more advanced applications, the reference design also includes an interface for dimming. The board itself does not include any signal generator, but to keep universality with different control schemes (analog or digital dimming) a three-pin connector was built in as depicted in Figure 3. A supply voltage of 6 V V CC can serve as an external PWM generator (implemented by either the microcontroller or by comparators). The PWM pin is an universal dimming input, working with both analog and digital dimming. Any voltage above 2.5 V is considered as 0% power, i.e. the analog dimming works in the range from 0 V to 2.5 V, where 0 V (grounding the pin) results in full power. The standard 3.3 V logic levels can be used as a PWM control signal for digital dimming. In this case the brightness changes from 0% (full power) to 99% (minimum power) duty cycle. If the driver is used without the PWM generator, pins 1 (GND) and 2 (PWM) on the PWM connector must be connected together.
3 Application
versions of output current) is 40 mm x 23 mm. Figure 4. PCB layout - top side Figure 5. PCB layout - bottom side
3.1 Measurement results
Several tests made on the reference design can be observed in Figure 8 through 11. Figure 8. Output current with 1 LED (Seoul Semiconductor P7) Figure 9. Dimming control curve (12 V input, 1 LED output)
4 Bill of material
Table 3. Bill of material
References and related materials UM0677 14/16 Doc ID 15396 Rev 2
5 References and related materials
- AN2129 - DIMMING OF SUPER HIGH BRIGHTNESS LEDS WITH L6902D - see www.st.com/stonline/products/literature/an/11247.pdf 2. AN1891 - APPLICA TION ID EAS: DRIVING LEDS USING L497X, L597X,L692X DC- DC CONVERTERS FAMILIES - see www.st.com/stonline/products/literature/an/ 10232.pdf 3. ST1S10 - 3 A, 900 kHz, monolithic synchronous step-down regulator - see www.st.com/stonline/products/literature/ds/13844.pdf 4. L6726A - Single phase PWM controller - see www.st.com/stonline/products/literature/ ds/12754.pdf 5. STS8DN3LLH5 - Dual N-channel 30 V , 0.0155 Ω, 10 A, SO-8 STripFET™ V Power MOSFET - see www.st.com/stonline/products/literature/ds/16967.pdf 6. STPS1L30M - LOW DROP POWER SCHOTTKY RECTIFIER - see www.st.com/ stonline/products/literature/ds/8902.pdf 7. TS821- 1.225V micropower shunt voltage reference - see www.st.com/stonline/ products/literature/ds/6877.pdf.
6 Revision history
Table 4. Document revision history 07-May-2009 1 Initial release.