LP6288 datasheet(13/24 Pages) POWER

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Preliminary Datasheet

LP6288

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LP6288

Version 0.1 JAN.-2018

Application Information

The LP6288 is a multi-channel power supply for TFT

LCD panels. It contains a boost regulator, three buck

regulators, a positive charge pump and a negative

charge pump, GPM, and temperature compensation

for positive voltage.

Under Voltage Lockout (UVLO)

The LP6288 had an UVLO internal circuit that enable

the device once the voltage on the VIN voltage

exceeds the UVLO threshold voltage.

Boost Converter (AVDD)

The LP6288 uses fixed-frequency, current mode

architecture to regulate the output voltage. The output

voltage and soft start time can be adjustable by

internal register(R[04h]).

Boost Loop Compensation

The voltage feedback loop can be compensated with

an external compensation network consisted of

Rcomp, Ccomp (As Figure 1,2). Choosing Rcomp to

set high frequency integrator gain for fast transient

response and Ccomp to set the integrator zero to

maintain loop stability.

Boost Over Voltage Protection

The boost converter has an over voltage protection to

protect the switch at the SWI pin. When the SWI

voltage rises above 21.5V(Typ.), the boost converter

will turns the MOS off and stop switching. Until the

output voltage falls below the over voltage threshold,

the converter will resume operation.

Boost Over Current Protection

The internal power MOS switch current is monitored

cycle-by-cycle and it's limited to set by R[03h] that the

value

not

exceed

3.4A(Typ.).

But

external

mode(R[20h]=0x01H), the OCP level can be set by

RCS(As Figure 2) 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.

Boost Under Voltage Protection

When SWO voltage is under 80% of the setting, the

LP6288 activation an internal timer. if the fault status

continues for 50ms, LP6288 will be shut down.

Boost Short Circuit Protection

The LP6288 incorporates an short circuit protection to

protect itself and external component. Any voltage

sense is lower than 40% of the setting voltage level, it

will be shut down immediately until VIN power cycled.

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.

VRIPPLE

RIPPLE(ESR)+VRIPPLE(C)

≅I

PEAK×RESR+

IPEAK

COUT

VOUT-VIN

VOUT×FOSC

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. A typical setting of the

inductor ripple current is 20% to 40% of the maximum

input current. If the selection is 40%, the maximum

peak inductor current is

IPEAK

IN(MAX)+0.5×IRIPPLE

=1.2×I

(MAX)

=1.2×�IOUT(MAX)×VOUT

��×V

(MIN) �

The minimum inductance value is derived from the

following equation :

=��×VIN(MIN)2×�VOUT-VIN(MIN)�

0.4×IOUT(MAX)×VOUT

×FOSC

Depending on the application, the recommended

inductor value is 6.8

μH.

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