LP3320-00

Jan.-2018

www.lowpowersemi.com

Page 5 of 9

Preliminary Datasheet

LP3320

Operation Information

LED Current Control

The LP3320 regulates the LED current by setting the

current sense resistor (R1) connecting to feedback

and ground. The internal feedback reference voltage

is 200mV. The LED current can be set from following

equation easily.

In order to have an accurate LED current, precision

resistors are preferred (1% is recommended). The

table for R1 selection is shown below.

Power Sequence

In order to assure the normal soft start function for

suppressing the inrush current the input voltage

should be ready before EN pulls high.

Soft-Start

The function of soft-start is made for suppressing the

inrush current to an acceptable value at the

beginning of power-on. The LP3320 provides a

built-in soft-start function by clamping the output

voltage of error amplifier so that the duty cycle of the

PWM will be increased gradually in the soft-start

period.

Current Limiting

The current flow through inductor as charging period

is detected by a current sensing circuit. As the value

comes across the current limiting threshold, the

N-MOSFET will be turned off so that the inductor will

be forced to leave charging stage and enter

discharging stage. Therefore, the inductor current

will not increase over the current limiting threshold.

OVP/UVLO/OTP

The Over Voltage Protection is detected by a

goes over the detecting voltage, LX pin stops

switching and the power N-MOSFET will be turned

off. As the output voltage is higher than a specified

value or input voltage is lower than a specified value,

the chip will enter protection mode to prevent

abnormal function. As the die temperature is higher

than 160℃, the chip also will enter protection mode.

The power MOSFET will be turned off during

protection mode to prevent abnormal operation.

Inductor Selection

The recommended value of inductor for 2 to 11

WLEDs applications are 2.2 to 10µH. Small size and

better efficiency are the major concerns for portable

device, such as LP3320 used for mobile phone. The

inductor should have low core loss at 1.0MHz and

low DCR for better efficiency. To avoid inductor

saturation current rating should be considered.

Capacitor Selection

Input ceramic capacitor of 2.2uF and output ceramic

capacitor of 1uF are recommended for the LP3320

applications for driving 11 series WLEDs.

For better voltage filtering, ceramic capacitors with

low ESR are recommended. X5R and X7R types are

suitable because of their wider voltage and

temperature ranges.