Preliminary Datasheet

LP3352

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LP3352 Version 0.2 AUG-2018

Application Information

The LP3352 is designed in a current mode, constant

frequency PWM boost converter. It can use dimming

input that can by external control signal with a duty

ratio of 1%-100% in 100Hz to 30kHz. The LP3352

include a boost converter with a built-in 2.5A/40V

power MOS, six LED string current sink regulators of

up to 30mA per channel, LED string open and short

detection, output over-current protection, over-voltage

protection, and over-temperature protection.

Under Voltage Lockout (UVLO)

The LP3352 had an UVLO internal circuit that enable

the device once the voltage on the VIN voltage

exceeds the UVLO threshold voltage.

Soft Start

To ensure a LED flash and low input inrush current

can be control, the chip features a built-in soft-start

current controller.

Boost Controller

The LP3352 uses 1MHz fixed-frequency, current

mode architecture to fixed the output current. The

output voltage automatically adjusts its voltage to the

Boost Over Current Protection

The internal power MOS switch current is monitored

cycle-by-cycle and current limited value not exceed

2.5A(Typ.). When the inductor current exceeds the

current limit, the switching will turns off immediately. It

prevents

large

current

damaging

the

external

component.

Output Over Voltage Protection

The LP3352 converter has an over voltage protection

by VOUT pin. When the LEDs fail open circuit or

LEDs are disconnected from the circuit, the over

voltage function will monitor the output voltage

through VOUT pin to protect the converter. When

LP3352 Output occur OVP, it will close LX function.

LED Current Setting

The LED current is specified by current sense resistor

between the ISET pin to ground. In order to have

accurate

LED

current,

precision

resistors

are

preferred. The LED current can be programmed by:

Dimming Control

The LED brightness is controlled by the PWM signal

at CTRL pin which has different duty cycle. LP3352

can accept an external PWM signal to CTRL pin in the

range of 100Hz to 30kHz.

Input Capacitor Selection

For

better

input

bypassing,

low-ESR

ceramic

capacitors are recommended for performance. A 2

0μF

input capacitor is sufficient for most applications. For a

lower output power requirement application, this value

can be decreased.

Boost Diode Selection

To achieve high efficiency, Schottky diode is good

choice for low forward drop voltage and fast switching

time. The output diode rating should be able to handle

the

maximum

output

voltage,

average

power

dissipation and the pulsating diode peak current.

Output Capacitor Selection

For lower output voltage ripple, low-ESR ceramic

capacitors

are

recommended.

The

tantalum

capacitors can be used as well, but the ESR is bigger

than ceramic capacitor. The output voltage ripple

consists of two components: one is the pulsating

output ripple current flows through the ESR, and the

other is the capacitive ripple caused by charging and

discharging.

=V

≅I

Inductor Selection

For a better efficiency in high switching frequency

converter, the inductor selection has to use a proper

core material such as ferrite core to reduce the core

loss and choose low ESR wire to reduce copper loss.

The most important point is to prevent the core

saturated when handling the maximum peak current.

Using a shielded inductor can minimize radiated noise

in sensitive applications. The maximum peak inductor

current is the maximum input current plus the half of

inductor ripple current. The calculated peak current

has to be smaller than the current limitation in the

electrical

characteristics.

Depending

on

the

application, the recommended inductor value is

between 4.7

μH to 10μH.

Over Temperature Protection

The

LP3352

device

enters

over

temperature

protection(OTP) if its junction temperature exceeds

160°C (Typ.). During over temperature protection

none of the device's functions are available. To

resume normal operation the junction temperature

need cool down, and the outputs will restart.