STEVAL-ILL008V1 STMicroelectronics, STEVAL-ILL008V1 Datasheet - Page 2

• 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

AN1941 APPLICATION NOTE
2 L6920D LED DRIVER
White LEDs are gaining popularity as sources of illumination because of their high efficiency
and reliability. Typical forward voltage drop of a white LED is approximately 3.5V. When these
LEDs are powered from a single or two cell batteries, a boost converter is needed to boost the
voltage to drive the LEDs.
2.1 L6920D Description
L6920D is a high efficiency step-up converter requiring very few external components to real-
ize the conversion from the battery voltage to the selected output voltage or current. The start-
up is guaranteed at 1V and the device is operating down to 0.6V. The device has very low qui-
escent current, only 10 A. Internal synchronous rectifier is implemented with a 120m
channel MOSFET, replacing the conventional boost diode, to improve the efficiency. This also
implies a reduced cost in the application since no external diode required.
Following is the block diagram of L6920D.
Figure 2. Block diagram of L6920D
In L6920D, the control is based on the comparator that continuously checks the status of the
feedback signal. If the feedback voltage is lower than reference value, the control function of
the L6920D directs the energy stored in the inductor to be transferred to the load. This is ac-
complished by alternating between two basic steps:
2/15
– Ton phase: the bottom MOFSET Q1 is turned on, and the inductor is charged. The switch
– Toff phase: the bottom MOSFET Q1 is turned off, and top MOSFET Q2 is turned on. The
SHDN
V
is turned off if the current reaches 1A or after a maximum on-time set to 5s.
energy stored in the inductor is transferred to the load for at least a minimum off time of
1s. After this, the synchronous switch is turned off as soon as the feedback signal goes
lower than reference or the current flowing in the inductor goes down to zero.
LBO
REF
A
B
C
-
+
-
+
Y
VBG
V
GND
R
Toff min
FB
1 sec
OUT
VBG
1
VBG
,R
+
-
2
OPAMP
LBI
Y
A
B
C
(CR)
Q
S
ZERO CROSSING
R
Ton max
5 sec
-
+
CURRENT LIMIT
- +
-
+
VOUT
D99IN1041
OUT
LX
GND
FB
V
IN
V
OUT
P-