Pin Configuration
SOT Pin No.
QFN Pin No.
Pin Name Pin Function
1
8
SW Power Switch Output. Connect the inductor and the blocking Schottky diode to SW. 2 1,5 GND Ground
3 6 FB Feedback input pin. The reference voltage at this pin is 104mV. Connect the cathode of the lowest LED to FB and a current n resistor between FB and GND.
4 4 EN Enable pin. A high input at EN enables the device and a low input disables the devices. When not ud, connect EN to the input source for automatic startup.
5 3 OV Over Voltage Input. OV measures the output voltage for open circuit protection. Connect OV to the output at the top of the LED string.
6
2
IN
Input Supply Pin. Must be locally bypasd.
General Description The OCP8106 is a step-up DC/DC converter designed for driving up to 8 white LEDs in ries from a single cell Lithium Ion battery with constant current. Becau it directly regulates output current, the OCP8106 is ideal for driving light emitting diodes (LEDs) who light intensity is proportional to the current passing through them, not the voltage across their terminals. A single external resistor ts LED current between 5mA and 20mA, which can then be easily adjusted using either a DC voltage or a pul width modulated (PWM) signal. Its low 104mV feedback voltage reduces power loss and improves efficiency. The OV pin monitors the output voltage and turns off the converter if an over-voltage condition is prent due to an open circuit condition. The OCP8106 is available in
TSOT23-6L and DFN8 packages. Features
z Drives Up to 5 Series White LEDs from 2.5V z Drives Up to 8 Series White LEDs from 3.6V z Up to 87% Efficiency
z 1.2MHz Fixed Switching Frequency z Low 104mV Feedback Voltage z Open Load Shutdown z Soft Start/PWM Dimming
z TSOT23-6L and DFN-8 Packages
Application
z Cell Phones
z Handheld Computers and PDAs z Digital Cameras z Small LCD Displays
Typical Application Circuit
FB
Figure 2.
Simplified Block Diagram of the OCP8106
SW
GND
5 10 15 20 25
90.00%
85.00%
80.00%
75.00%
Efficiency vs n(LED)
I o u t ( m A ) V i n = 3 . 6 V写草莓的作文
Absolute Maximum Ratings (Note 1)
SYMBOL NAME VALUE UNIT V IN Input Voltage -0.3～6 V V SW Voltage at SW Pin -0.5～35
V V IO All Other I/O Pins GND-0.3 to VDD+0.3 V P TR1 Thermal Resistance, SOT-23-6 ΘJA ΘJC
220
菠萝炒肉的做法110
℃/W
P TR2 Thermal Resistance ，
QFN-8 (2mm x 2mm) ΘJA
ΘJC
80
16
℃/W T stg Storage Temperature -55 to 150 ℃ T solder Package Lead Soldering Temperature 260℃, 10s
Note1: Exceeding the ratings may damage the device.
Recommended Operating Conditions (Note 2)
SYMBOL NAME
VALUE UNIT V IN VIN Supply Voltage 2.5 to +6 V V SW Output Voltage
V IN to 28 V T OPT
Operating Temperature
-40 to +85 ℃
Note2: The device is not guaranteed to function outside of its operating rating.
Electrical Characteristics
(V IN =V EN =3V, T opt =25°C unless specified otherwi.) SYMBOL ITEMS CONDITIONS Min. Typ. Max.UNIT V IN Input Voltage 2.5 6 V Feedback
V FB FB Pin Voltage Driving 4xLED @15mA 94 104 114 mV I bias FB Pin Input Bias Current 0.05 1 µA Operating Current
I off Operating Current （Shutdown ） V SW-ON =
0V 0.1 1 µA I sby Operating Current （Quiescent ） V FB =
0.3V 100 350 µA F sw Switching Frequency 1.0 1.25 1.5 MHz D max Maximum Duty Cycle V FB =0V 85 90 % Chip Enable V EN_H EN Minimum High Level 1.5 V V EN_L EN Maximum Low Level 0.4 V V HYS EN Hysteresis 90 mV EN Input Bias Current V SW-ON =0V, 5V 1 µA Output Switch
R ON SW On Resistance (Note 3) 0.5 Ω I LIMIT SW Current Limit 400 mA
收敛思维I LEAK SW Leakage Current V sw ＝5V
0.01 1 µA Open Circuit Protection
V OV Open Circuit Shutdown Threshold V OV Rising 30 V Soft Start花菖蒲
t ss Soft Start Time (Note 3) V IN Power On 160 µS Note3: Guaranteed by design.
Typical Performance Characteristics
Driving Capability
Vin I LED =15mA I LED =20mA 2.5V 5 x LED 4 x LED 3.0V 6 x LED 5 x LED 3.6V
8 x LED 8 x LED
Q u i e s c e n t C u r r e n t (μA )
S w i t c h i n g F r e q u e n c y (M H z )
OPERATION
The OCP8106 us a constant frequency, peak current mode boost regulator architecture to regulate the ries string
of white LEDs. The operation of the OCP8106 can be understood by referring to the simplified block diagram shown
南通特产
above. At the start of each oscillator cycle, the control logic turns on the power switch M1. The signal at the
non-inverting input of the PWM comparator is proportional to the switch current, summed together with a portion of
the oscillator ramp. When this signal reaches the level t by the output of error amplifier, the PWM comparator rets
the latch in the control logic and turns off the power switch. In this manner, error amplifier ts the correct peak current
level to keep the LED current in regulation. If the feedback voltage starts to drop, the output of the error amplifier
increas. This results in more current to flow through M1, hence increasing the power delivered to the output.
Application Information
Inductor Selections
For most of the applications of the OCP8106, it is recommended to u an inductor of 22uH. Although small size is
one of the major factors in lecting an inductor, the smaller and thinner inductors give higher core loss at
1.25MHz and DRC, resulting in lower efficiencies. The following tab le provides a list of recommended inductors:
PART NUMBER DCR（Ω）CURRENT RATING（mA）MANUFACTURER LQH3C220 0.71 250 MURATA CDRH3D16-220 0.53 350 SUMIDA LB2012B220M 1.7 75 TAIYO
YUDEN LEM2520-220 5.5 125 TAIYO
YUDEN EJPC220KF 4.0 160 PANASONIC Capacitor Selection
The small size of ceramic capacitors makes them ideal for OCP8106 applications. X5R and X7R types are recommended becau they retain their capacitance over wider voltage and temperature ranges than other types
such as Y5V or Z5U. A 1µF input capacitor and a 0.22 µF output capacitor are sufficient for most OCP8106 applications.
Diodes Selection
Schottky diodes, with their low forward voltage drop and fast rever recovery, are the ideal choices for OCP8106 applications. The forward voltage drop of a Schottky diode reprents the conduction loss in the diode, while the
diode capacitance (C T or C D) reprents the switching loss. For diode lection, both forward voltage drop and
diode capacitance need to be considered. Schottky diodes with higher current ratings usually have lower forward
voltage drop and larger diode capacitance, which can cau significant switching loss at the 1.25MHz switching儿子生日祝福
frequency of the OCP8106. A Schottky diode rated at 100mA to 200mA is sufficient for most OCP8106 applications.
Some recommended Schottky diodes are listed in the following table:
PART NUMBER FORWARD CURRENT
（mA）
VOLTAGE DROP
（V）
白羊和狮子DIODE CAPACITANCE
（pF）
MMANUFACTURER
CMDSH-3 100 0.58@100mA 7.0@10V Central
CMDSH2-3 200 0.49@200mA 15@10v Central
BAT54 200
0.53@100mA
10@25v Zetex
LED Current Control
The LED current is controlled by the feedback resistor. The feedback reference is 104mV. The LED current is
104mV/Rfb. In order to have accurate LED current, precision resistors are preferred (1% is recommended). The
formula and table for RFB lection are shown below:
R FB = 104mV/I LED
金丝峡景区I LED（mA）R FB Value（Ω）
5 20.8
10 10.4
15 6.93
20 5.2
Open Circuit Protection
Open circuit protection will shut off the OCP8106 if the output voltage goes too high when the OV pin is tied to the
output. In some cas an LED may fail, which will result in the feedback voltage always being zero. The OCP8106
will then switch at its maximum duty cycle boosting the output voltage higher and higher. By connecting the OV pin
to the top of the LED string the OCP8106 checks this condition and if the output ever exceeds 30V, the OCP8106
will shut down. The part will not switch again until the power is recycled.
Dimming Control
There are three different types of dimming control circuits: 1. Using a DC Voltage
For some applications, the preferred method of brightness control is a variable DC voltage to adjust the LED current. The dimming control using a DC voltage is shown in Figure 3. As the DC voltage increas, the voltage drop on R2 increas and the voltage drop on R1 decreas. Thus, the LED current decreas. The lection of R2 and R3 will make the current from the variable DC source much smaller than the LED current and much larger than the FB pin bias current.
2. Using a PWM Signal to EN Pin
With the PWM signal applied to the EN pin, the OCP8106 is turned on or off by the PWM signal. The LEDs operate at either zero or full current. The average LED current increas proportionally with the duty cycle of the PWM signal. A 0% duty cycle will turn off the OCP8106 and corresponds to zero LED current. A 100% duty cycle corresponds to full current. The typical frequency range of the PWM signal should be 1kHz or less due to the soft start function.
Ω
Figure 3. Dimming Control Using a DC Voltage
Ω
Figure 4. Dimming Control Using a PWM Signal
