Preliminary Datasheet

LP6229

LP6229 –00 Version 1.0 Datasheet

Jul.-2013

Page 4 of 6

Operation Information

The LP6229 uses a 1.1MHz fixed-frequency,

current-mode regulation architecture to regulate the

output voltage. The LP6229 measures the output

voltage through an external resistive voltage divider

and compares that to the internal 0.6V reference to

generate the error voltage to the inductor current to

regulate the output voltage. the use of current-mode

regulation improves transient response and control

loop stability.

When the LP6229 is disable(EN=Low),both power

switches are off. There is no current path from SW

to OUT. There fore, the output voltage discharges to

ground. When the LP6229 is enabled(EN=High),a

limited start-current charges the output voltage

rising to SW, then the part operates in force PWM

mode for regulating the output voltage to the target

value. At the beginning of each cycle, the N-channel

MOSFET switch is turned on, forcing the inductor

current to rise, The current at the source of the

switch is internally measured and converted to a

voltage by the current sense amplifier. That voltage

is compared to the error voltage. When the inductor

current rises sufficiently, the PWM comparator

turns off the switch, forcing the inductor current to

the output capacitor through the internal P-Channel

MOSFET rectifier, which forces the inductor

current to decrease. The peak inductor current is

controlled by the error voltage. Thus the output

voltage controls the inductor current to satisfy the

lode.

Setting the Output Voltage

Set the output voltage by selecting the resistive

voltage divider ratio. The voltage divider drops the

output voltage to the 0.6V feedback voltage. Use a

100K resistor for R2 of the voltage divider.

Determine the high-side resistor R1 by the equation:

Current Limitation

The internal power-MOS switch current is monitored

cycle-by-cycle and is limited to the value not exceed

1.5A (Typ.). When the switch current reaches the

limited value, the internal power-MOS is turned off

immediately until the next cycle.

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

The minimum inductance value is derived from the

following equation :

Depending on the application, the recommended

inductor value is between 2.2μH to 4.7μH.

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.