LP6253 datasheet(8/11 Pages) POWER

8 / 11 page

Preliminary Datasheet

LP6253

LP6253 –00

Version 1.0

Sep.-2013

Email: marketing@lowpowersemi.com

www.lowpowersemi.com

Page 8 of 11

Low Battery Detection ---- LBI/LBO(for LP6253QVF)

The LP6253 low-battery detector circuit is typically

used to supervise the battery voltage and to generate

an error flag when the battery voltage drops below a

user-set threshold voltage. The function is active only

when the device is enabled. When the device is

disabled, the LBO pin is high-impedance. The

switching threshold is 500 mV at LBI. During normal

operation, LBO stays at high impedance when the

voltage, applied at LBI, is above the threshold. It is

active low when the voltage at LBI goes below 500

mV.

The battery voltage, at which the detection circuit

switches, can be programmed with a resistive divider

connected to the LBI pin. The resistive divider scales

down the battery voltage to a voltage level of 500

mV, which is then compared to the LBI threshold

voltage. The LBI pin has a built-in hysteresis of

10mV, If the low-battery detection circuit is not used,

the LBI pin should be connected to GND (or to

VBAT) and the LBO pin can be left unconnected. Do

not let the LBI pin float.

The recommended value for R2 is therefore in the

range of 500kΩ. From that, the value of resistor R1,

depending on the desired minimum battery voltage

VBAT, can be calculated using:

LP6253QVF:R1=(VBAT/0.5V-1)×R2

Setting the Output Voltage

Set the output voltage by selecting the resistive

voltage divider ratio. The voltage divider drops the

output

voltage

the

0.5V(LP6253QVF)/

0.8V(LP6253SPF) feedback voltage. Use a 10K

resistor for R4 of the voltage divider. Determine the

high-side resistor R3 by the equation:

Vout=(R3/R4+1)×VFB

Low-EMI Switch

The device integrates a circuit that removes the

ringing that typically appears on the SW node when

the converter enters discontinuous current mode. In

this case, the current through the inductor ramps to

zero and the rectifying PMOS switch is turned off to

prevent a reverse current flowing from the output

capacitors back to the battery. Due to the remaining

energy that is stored in parasitic components of the

semiconductor and the inductor, a ringing on the SW

pin is induced. The integrated

antiringing switch clamps this voltage to VBAT and

therefore dampens ringing.

Pre-Boost Current and Short Circuit Protect

Initially output voltage is lower than battery voltage,

and the LP6253 enters pre-boost phase. During

pre-boost phase, the internal NMOSFET/PMOSFET

is turned off/on and a constant current is provided

from battery to output until the output voltage close

to the battery voltage. The constant current is limited

by internal controller. If the output short to ground,

the LP6253 also limits the output current to avoid

damage condition.

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 10μH.

Input Capacitor Selection

For

better

input

bypassing,

low-ESR

ceramic

capacitors are recommended for performance. A

10μF input capacitor is sufficient for most

applications. A ceramic capacitor or a tantalum

capacitor with a 100nF ceramic capacitor in parallel,

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