Preliminary Datasheet

LP3351

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Page 6 of 7

LP3351 Version 0.3 MAR-2018

Application Information

The LP3351 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 1kHz. LP3351 offers

protection features to protect the system such as

output

over

voltage

protection,

boost

diode

disconnection

protection,

output

short

circuit

protection and over temperature protection.

Under Voltage Lockout (UVLO)

The LP3351 had an UVLO internal circuit that enable

the device once the voltage on the VIN voltage

exceeds the UVLO threshold voltage.

Boost Controller

The LP3351 uses 200kHz fixed-frequency, current

mode architecture to fixed the output current. The

output voltage and soft start time can be adjustable by

internal register.

Boost Loop Compensation

The feedback loop can be compensated with an

external compensation network consisted of Rcomp,

Ccomp(As Figure 1). Choosing Rcomp to set high

frequency integrator gain for fast transient response

and Ccomp to set the integrator zero to maintain loop

stability.

Over Voltage Protection

The LP3351 converter has an over voltage protection

by OVP pin. When the LEDs fail open circuit or LEDs

are disconnected from the circuit, the over voltage

function will monitor the output voltage through OVP

pin to protect the converter. When LP3351 occur

OVP, it will latch off until VIN is re-startup or CTRL

input is recycled.

LED Current Setting

The LED current is specified by current sense resistor

between the FB 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. LP3351

can accept an external PWM signal to CTRL pin in the

range of 100Hz to 1 kHz.

Over Temperature Protection

The

LP3351

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.

Current Sense and Over Current Protection (OCP)

The over current protection level can be set by R7(As

Figure 1) and senses inductor current to compare with

current limit value. When the inductor current exceeds

the

current

limit,

the

switching

will

turns

off

immediately. It prevents large current damaging the

external component. The OCP level is calculated as:

The LP3351 uses a current mode control structure.

The CS pin not only has current sense function but

also

build-in

a

slope

compensation

to

avoid

sub-harmonic

oscillation.

Additional

slope

compensation lessened the influence of the sensed

current in the control loop.

Layout Guideline

The proper PCB layout and component placement are

critical for all circuit. The careful attention should be

prevent electromagnetic interference (EMI) problems.

Here are some suggestions to the layout of LP3351

design.

1.

Connected

all

ground

together

with

one

uninterrupted ground plane with at least two vias .

2. The input capacitor should be located as closed as

possible to the VIN and ground plane.

3. Minimize the distance of all traces connected to the

LX node, that the traces short and wide route to obtain

optimum efficiency.

4. All output capacitor must be closed to ground

plane. The ground terminal of COUT must be located

as closed as possible to ground plane.

5. Radiated noise can be decreased by choosing a

shielded inductor.

L

Diode

GND

VIN

GND

V+

V-

1

2

3

4

5

6

7

8

LP3351

G

S

GND

Figure 4. Recommended PCB Layout Diagram

.