STEVAL-ILL008V1 STMicroelectronics, STEVAL-ILL008V1 Datasheet - Page 7

• Manufacturer Part Number: STEVAL-ILL008V1
• Description: EVAL BOARD CREE LED FLASHLIGHT
• Manufacturer: STMicroelectronics

Specifications of STEVAL-ILL008V1

• Mfg Application Notes: Low Voltage LED Driver AppNote
• Design Resources: STEVAL-ILL008V1 Gerber Files STEVAL-ILL008V1 Schematic STEVAL-ILL008V1 Bill of Materials
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 3.5V
• Features: 1V Start up Input Voltage
• Voltage - Input: 1 ~ 5.5 V
• Utilized Ic / Part: L6920
• Product: Display Modules
• Core Chip: L6920DA
• Output Voltage: 3.5V
• Kit Contents: L6920D, L4971, L6902D Reference Board
• Development Tool Type: Hardware - Eval/Demo Board
• Tool / Board Applications: LED Flashlight
• Mcu Supported Families: L6920DA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output / Channel: -
• Lead Free Status / Rohs Status: Details
• Other names: 497-5516

The brightness is directly proportional to the current driving the LED. A test was conducted in
a closed box with a white LED mounted 12 inches away from the light meter. The results
showed a linear relationship between current and light output. The graph in figure 2.3 also
shows the relation between current and forward drop of the LED.
When driving LEDs from a DC-DC buck topology the minimum voltage input that the power
supply will operate, the maximum voltage input and the maximum power capability of the unit
must be taken into account. Table 2.2 shows the capability of the L4971 and L6902D reference
designs for minimum input voltage and the maximum input voltage.
Table 3.
Figure 10.
3.2 L4971 LED Driver
The L4971 is a step down monolithic power switching regulator able to deliver 1.5A. Its con-
struction is BCD mixed technology using an internal D-MOS transistor with low Rdson to obtain
high efficiency and high switching speeds. Features of this DC-DC converter are pulse by
pulse current limit; hiccup mode for short circuit protection, voltage feed forward, soft start and
thermal shutdown. Typically it is used for regulating an output voltage. An output current can
also be regulated by sensing the voltage drop across a sense resistor, Rs as shown on the
following schematic.
Control
L6902D
L6902D
L4971
L4971
V in
25
20
55
8
# LEDs
1
6
5
9
AN1941 APPLICATION NOTE
220-400mA
220-400mA
Current
350mA
350mA
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