LTC3230 datasheet(13/16 Pages) LINER

13 / 16 page

LTC3230

3230fa

APPLICATIONS INFORMATION

of capacitor is needed to ensure minimum capacitances

at all temperatures and voltages.

Table 3 shows a list of ceramic capacitor manufacturers

and how to contact them.

Table 3. Recommended Capacitor Vendors

AVX

xww.avxcrp.com

Kemet

www.kemet.com

Murata

www.murata.com

Taiyo Yuden

www.t-yuden.com

Vishay

www.vishay.com

Layout Considerations and Noise

Due to the high switching frequency and the transient

currents produced by the LTC3230, careful board layout

is necessary. A true ground plane and short connections

to all capacitors will improve performance and ensure

proper regulation under all conditions.

The ﬂying capacitor pins C1P, C2P, C1M and C2M will have

high edge rate waveforms. The large dv/dt on these pins

can couple energy to adjacent PCB runs. Magnetic ﬁelds

can also be generated if the ﬂying capacitors are not close

to the LTC3230 (i.e., the loop area is large). To decouple

capacitive energy transfer, a grounded PCB trace between

the sensitive node and the LTC3230 pins will shield the

sensitive node. For a high quality AC ground, the shield

trace should be returned to a solid ground plane that

extends all the way to the LTC3230.

The following guidelines should be followed when design-

ing a PCB layout for the LTC3230:

• The Exposed Pad should be soldered to a large cop-

per plane that is connected to a solid, low impedance

ground plane using plated through hole vias for proper

heat sinking and noise protection.

• Input and output capacitors must be placed close to

the part.

• The ﬂying capacitors must be placed close to the part.

The traces from the pins to the capacitor pad should

be as wide as possible.

• VINandCPOtracesmustbewidetominimizeinductance

and handle high currents.

• LED pads must be large and connected to the other

layers of metal to ensure proper heat sinking.

• The RSET pin is sensitive to noise and capacitance. The

resistor should be placed near the part with minimum

line width.

Power Efﬁciency

To calculate the power efﬁciency (

η) of a white LED

driver chip, the LED power should be compared to the

input power. The difference between these two numbers

represents lost power whether it is in the charge pump

or the current sources. Stated mathematically, the power

efﬁciency is given by:

η=

LED

The efﬁciency of the LTC3230 depends upon the mode in

which it is operating. Recall that the LTC3230 operates

as a pass switch, connecting VIN to CPO, until dropout is

detected at a LED pin. This feature provides the optimum

efﬁciency available for a given input voltage and LED

forward voltage. When it is operating as a switch, the

efﬁciency is approximated by:

η=

LED

•

since the input current will be very close to the sum of

the LED currents.

At moderate to high output power, the quiescent current

of the LTC3230 is negligible and the expression above is

valid.

Once dropout is detected at any LED pin, the LTC3230

enables the charge pump in 1.5x mode.

In 1.5x boost mode, the efﬁciency is similar to that of a

linear regulator with an effective input voltage of 1.5 times

the actual input voltage. This is because the input current

for a 1.5x charge pump is approximately 1.5 times the

load current. In an ideal 1.5x charge pump, the power

efﬁciency would be given by:

η=

LED

•

•. •

. •

LTC3230 Datasheet(PDF) 13 Page - Linear Technology

LTC3230 Datasheet(HTML) 13 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Datasheet Download

Link URL