LTC3621 datasheet(13/20 Pages) AD

13 / 20 page

LTC3644/LTC3644-2

Rev. 0

For more information www.analog.com

APPLICATIONS INFORMATION

Table 2. Recommended Inductors for 1.25A Buck Regulators

PART NUMBER

L (μH)

MAX DCR (mΩ)

MAX IDC (A)

SIZE IN mm (L × W × H)

MANUFACTURER

DFE201612E1R5MP2

1.5

3.2

2 × 1.6 × 1.2

Murata

74438356015

1.5

5.8

4.1 × 4.1 × 2.1

Wurth Elektronik

IHLP1212BZER2R2M11

2.2

42.9

3.3

3 × 3 × 0.8

Vishay

XAL4020222ME

2.2

35.2

5.6

4 × 4 × 2.1

Coilcraft

XAL4030332ME

3.3

5.5

4 × 4 × 3.1

Coilcraft

74438356033

3.3

39.9

3.6

4.1 × 4.1 × 2.1

Wurth Elektronik

IHLP2020CZER4R7M11

4.7

5.2

5.2 × 5.2 × 3

Vishay

Table 3. Recommended Inductors for 2.5A Buck Regulators

PART NUMBER

L (μH)

MAX DCR (mΩ)

MAX IDC (A)

SIZE IN mm (L × W × H)

MANUFACTURER

XAL4020102ME

13.25

8.7

4 × 4 × 2.1

Coilcraft

74437324010

4.5 × 4.1 × 1.8

Wurth Elektronik

XAL4020152ME

1.5

21.45

7.1

4 × 4 × 2.1

Coilcraft

74438356022

2.2

4.7

4.1 × 4.1 × 2.1

Wurth Elektronik

IHLP2020CZER2R2M11

2.2

22.5

5.5

5.2 × 5.2 × 3

Vishay

SPM6530T3R3M

3.3

7.3

7.1 × 6.5 × 3

TDK

Table 4. Recommended Inductors for 3.75A Buck Regulators

PART NUMBER

L (μH)

MAX DCR (mΩ)

MAX IDC (A)

SIZE IN mm (L × W × H)

MANUFACTURER

XAL4020601ME

0.6

9.5

10.4

4 × 4 × 2.1

Coilcraft

744383560068

0.68

7.5

9.4

4.1 × 4.1 × 2.1

Wurth Elektronik

XEL4020821ME

0.82

11.8

10.2

4 × 4 × 2.1

Coilcraft

IHLP2020CZER1E0M11

6.5

5.2 × 5.2 × 3

Vishay

FDV0530H1R0M

11.2

8.4

6.2 × 5.8 × 3

Murata

SPM5030T2R2MHZ

2.2

19.3

8.5

5.2 × 5 × 3

TDK

2. The switching current is the sum of the MOSFET

driver and control currents. The power MOSFET driver

current results from switching the gate capacitance of

the power MOSFETs. Each time a power MOSFET gate

is switched from low to high to low again, a packet of

charge dQ moves from VIN to ground. The resulting

dQ/dt is a current out of VIN that is typically much

larger than the DC control bias current. In continuous

mode, IGATECHG = fOSC(QT + QB), where QT and QB are

the gate charges of the internal top and bottom power

MOSFETs and fOSC is the switching frequency. The

power loss is thus:

Switching Loss = IGATECHG • VIN

The gate charge loss is proportional to VIN and fOSC

and thus their effects will be more pronounced at

higher supply voltages and higher frequencies.

3. Other“hidden”lossessuchastransitionlossandcopper

trace and internal load resistances can account for

additional efficiency degradations in the overall power

system. It is very important to include these “system”

level losses in the design of a system. Transition loss

arises from the brief amount of time the top power

MOSFET spends in the saturated region during

switch node transitions. The LTC3644 internal power

devices switch quickly enough that these loses are not

significant compared to other sources. These losses

plus other losses, including diode conduction losses

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