LTC7802EUFDM datasheet(16/34 Pages) AD

16 / 34 page

LTC7802

Rev. 0

For more information www.analog.com

To properly dimension the external filter components, the

DCR of the inductor must be known. It can be measured

using a good RLC meter, but the DCR tolerance is not

always the same and varies with temperature; consult

the manufacturers’ data sheets for detailed information.

Using the maximum inductor current (IL(MAX)) and ripple

current (ΔIL) from the Inductor Value Calculation section,

the target sense resistor value is:

RSENSE(EQUIV) =

VSENSE(MAX)

ILMAX+

ΔIL

To ensure that the application will deliver full load cur-

rent over the full operating temperature range, choose

the minimum value for VSENSE(MAX) in the Electrical

Characteristics table.

Next, determine the DCR of the inductor. When provided,

use the manufacturer’s maximum value, usually given at

20°C. Increase this value to account for the temperature

coefficient of copper resistance, which is approximately

0.4%/°C. A conservative value for TL(MAX) is 100°C. To

scale the maximum inductor DCR to the desired sense

resistor value, use the divider ratio:

RD =

RSENSE(EQUIV)

DCRMAX atTL(MAX)

C1 is usually selected to be in the range of 0.1μF to 0.47μF.

This forces R1||R2 to around 2k, reducing error that might

have been caused by the SENSE+ pin’s ≈1μA current.

The target equivalent resistance R1||R2 is calculated from

the nominal inductance, C1 value, and DCR:

R1!R2 =

(DCR at 20

°C) • C1

The sense resistor values are:

R1!R2

; R2

R1•RD

−RD

The maximum power loss in R1 is related to duty cycle and

occurs in continuous mode at the maximum input voltage:

PLOSS R1=

(VIN(MAX) − VOUT)• VOUT

Ensure that R1 has a power rating higher than this value.

If high efficiency is necessary at light loads, consider this

power loss when deciding whether to use DCR sensing

or sense resistors. Light load power loss can be mod-

estly higher with a DCR network than with a sense resis-

tor, due to the extra switching losses incurred through

R1. However, DCR sensing eliminates a sense resistor,

reduces conduction losses and provides higher efficiency

at heavy loads. Peak efficiency is about the same with

either method.

APPLICATIONS INFORMATION

Figure 2. Current Sensing Methods

(2a) Using a Resistor to Sense Current

(2b) Using the Inductor DCR to Sense Current

7802 F02b

LTC7802

BOOST

SENSE1, 2+

SENSE1, 2–

GND

VIN1,2

VOUT1,2

C1*

*PLACE C1 NEAR SENSE PINS

RSENSE(EQ) = DCR(R2/(R1+R2))

DCR

INDUCTOR

(R1||R2) • C1 = L/DCR

RSENSE ESL

LTC7802

BOOST

SENSE1,2+

SENSE1,2–

VOUT1,2

VIN1,2

PLACE RF AND CF NEAR SENSE PINS

SENSE RESISTOR

WITH PARASITIC

INDUCTANCE

RF*CF = ESL/RSENSE

POLE-ZERO

CANCELLATION

7802 F02a

LTC7802EUFDM 数据表(PDF) 16 Page - Analog Devices

LTC7802EUFDM 数据表(HTML) 16 Page - Analog Devices

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 25 26 27 28 29 30 31 32 33 34

数据表下载

链接网址

LTC7802EUFDM 数据表(PDF) 16 Page - Analog Devices

LTC7802EUFDM 数据表(HTML) 16 Page - Analog Devices

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 25 26 27 28 29 30 31 32 33 34

数据表 下载

链接网址

数据表下载