LTC4100 datasheet(19/24 Pages) LINER

19 / 24 page

LTC4100

sn4100 4100is

APPLICATIO S I FOR ATIO

Table 10 Recommended Inductor Values

Maxaimum

Input

Minimum Inductor

Average Current (A)

Voltage (V)

Value (

µH)

≤20

± 20%

>20

± 20%

≤20

± 20%

>20

± 20%

≤20

± 20%

>20

± 20%

≤20

± 20%

>20

± 20%

Calculating IC Power Dissipation

The power dissipation of the LTC4100 is dependent upon

the gate charge of the top and bottom MOSFETs (Q2 & Q3

respectively) The gate charge (QG) is determined from the

manufacturer’s data sheet and is dependent upon both the

gate voltage swing and the drain voltage swing of the

MOSFET. Use 6V for the gate voltage swing and VDCIN for

the drain voltage swing.

PD = VDCIN • (fOSC (QGQ2 + QGQ3) + IDCIN)

Example: VDCIN = 19V, fOSC = 345kHz, QGQ2 = 25nC,

QGQ3 = 15nC, IDCIN = 3mA.

PD = 320mW

Soft Start and Undervoltage Lockout

The LTC4100 is soft started by the 0.12

µF capacitor on the

ITH pin. On start-up, ITH pin voltage will rise quickly to 0.5V,

then ramp up at a rate set by the internal 30

µA pull-up

current and the external capacitor. Battery charging

current starts ramping up when ITH voltage reaches 0.8V

and full current is achieved with ITH at 2V. With a 0.12µF

capacitor, time to reach full charge current is about 2ms

and it is assumed that input voltage to the charger will

reach full value in less than 2ms. The capacitor can be

increased up to 1

µF if longer input start-up times are

needed.

Table 9. Recommended Resistor Values

IMAX (A)

RSENSE (Ω) 1%

RSENSE (W)

RILIM (Ω) 1%

1.023

0.100

0.25

2.046

0.05

0.25

10k

3.068

0.025

0.5

33k

4.092

0.025

0.5

Open

Warning

DO NOT CHANGE THE VALUE OF RILIM DURING OPERA-

TION. The value must remain fixed and track the RSENSE

value at all times. Changing the current setting can result

in currents that greatly exceed the requested value and

potentially damage the battery or overload the wall adapter

if no input current limiting is provided.

Inductor Selection

Higher operating frequencies allow the use of smaller

inductor and capacitor values. A higher frequency gener-

ally results in lower efficiency because of MOSFET gate

charge losses. In addition, the effect of inductor value on

ripple current and low current operation must also be

considered. The inductor ripple current

∆IL decreases

with higher frequency and increases with higher VIN.

∆I

OUT

= ()( )

−









Accepting larger values of

∆IL allows the use of low

inductances, but results in higher output voltage ripple

and greater core losses. A reasonable starting point for

setting ripple current is

∆IL = 0.4(IMAX). Remember the

maximum

∆IL occurs at the maximum input voltage. The

inductor value also has an effect on low current operation.

The transition to low current operation begins when the

inductor current reaches zero while the bottom MOSFET is

on. Lower inductor values (higher

∆IL) will cause this to

occur at higher load currents, which can cause a dip in

efficiency in the upper range of low current operation. In

practice 10

µH is the lowest value recommended for use.

LTC4100 bảng dữ liệu(PDF) 19 Page - Linear Technology

LTC4100 bảng dữ liệu(HTML) 19 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

bảng dữ liệu tải về

Link URL