LT3682EDD データシートの表示（PDF） - Linear Technology

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LT3682EDD

1A Micropower Step-Down Switching Regulator

Linear Technology 

LT3682

APPLICATIONS INFORMATION

Table 3. Schottky Diodes

PART NUMBER VR (V)

On Semiconducor

MBR0520L

20

MBR0540

40

MBRM120E

20

MBRM140

40

Diodes Inc.

B0530W

30

B0540W

40

B120

20

B130

30

B140

40

B150

50

B220

20

B230

30

B140HB

40

DFLS240L

40

DFLS140

40

B240

40

Central Semiconductor

CMSH1 – 40M

40

CMSH1 – 60M

60

CMSH1 – 40ML 40

CMSH2 – 40M

40

CMSH2 – 60M

60

CMSH2 – 40L

40

CMSH2 – 40

40

CMSH2 – 60

60

IAVE (A)

0.5

0.5

1

1

0.5

0.5

1

1

1

1

2

2

1

2

1.1

2

1

1

1

2

2

2

2

2

VF at 1A (mV) VF at 2A (mV)

620

530

595

550

620

500

500

500

700

500

500

500

510

500

500

700

400

550

700

400

500

700

Frequency Compensation

The LT3682 uses current mode control to regulate the

output. This simplifies loop compensation. In particular,

the LT3682 does not require the ESR of the output capacitor

for stability, so you are free to use ceramic capacitors to

achieve low output ripple and small circuit size. Frequency

compensation is provided by the components tied to the VC

pin, as shown in Figure 2. Generally a capacitor (CC) and a

resistor (RC) in series to ground are used. In addition, there

may be a lower value capacitor in parallel. This capacitor

(CF) is used to filter noise at the switching frequency, and

is required only if a phase-lead capacitor (CPL) is used or

if the output capacitor has high ESR.

LT3682

CURRENT MODE

SW

POWER STAGE

gm = 1.25S

FB

gm = 420μS

0.8V

3Meg

VC

GND

CF

RC

CC

OUTPUT

R1

CPL

ESR

+

C1

C1

POLYMER

OR

TANTALUM

R2

OR

ELECTROLITIC

CERAMIC

3682 F02

Figure 2. Model for Loop Response

Loop compensation determines the stability and transient

performance. Optimizing the design of the compensation

network depends on the application and type of output

capacitor. A practical approach is to start with one of the

circuits in this data sheet that is similar to your application

and tune the compensation network to optimize the

performance. Stability should then be checked across all

operating conditions, including load current, input voltage

and temperature. The LT1375 data sheet contains a more

thorough discussion of loop compensation and describes

how to test the stability using a transient load. Figure 2

shows an equivalent circuit for the LT3682 control loop.

The error amplifier is a transconductance amplifier with

finite output impedance. The power section, consisting

of the modulator, power switch and inductor, is modeled

as a transconductance amplifier generating an output

current proportional to the voltage at the VC pin. Note that

the output capacitor integrates this current, and that the

3682f

16

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