LTC1753CSW 查看數據表（PDF） - Linear Technology

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LTC1753CSW

5-Bit Programmable Synchronous Switching Regulator Controller for Pentium® III Processor

Linear Technology 

LTC1753

APPLICATIO S I FOR ATIO

The RDS(ON) required for a given conduction loss can now

be calculated by rearranging the relation P = I2R.

( ) ( ) RDS ON Q1 =

( ) ( ) PMAX Q1

=

VIN

PMAX

Q1





2

2

[ ( )]( ) ( )( ) DC Q1 IMAX

VOUT IMAX

( ) ( ) RDS ON Q2 =

( ) PMAX Q2

=

2

( ) VIN

PMAX

Q2





2

[ ( )]( ) ( )( ) DC Q2 IMAX

VIN − VOUT IMAX

PMAX should be calculated based primarily on required

efficiency or allowable thermal dissipation. A typical high

efficiency circuit designed with a 5V input and a 2.8V,

11.2A output might allow no more than 4% efficiency loss

at full load for each MOSFET. Assuming roughly 90%

efficiency at this current level, this gives a PMAX value of:

[(2.8)(11.2A/0.9)(0.04)] = 1.39W per FET

and a required RDS(ON) of:

(5V)(1.39W)

( )( ) ( ) RDS ON Q1 =

= 0.019Ω

2

2.8V 11.2A

(5V)(1.39W)

( )( ) ( ) RDS ON Q2 =

= 0.025Ω

2

5V − 2.8V 11.2A

Note also that while the required RDS(ON) values suggest

large MOSFETs, the dissipation numbers are only 1.39W

per device or less––large TO-220 packages and heat sinks

are not necessarily required in high efficiency applica-

tions. Siliconix Si4410DY or International Rectifier IRF7413

(both in SO-8) or Siliconix SUD50N03 or Motorola

MTD20N03HDL (both in D PAK) are small footprint sur-

face mount devices with RDS(ON) values below 0.03Ω at 5V

of gate drive that work well in LTC1753 circuits. With

higher output voltages, the RDS(ON) of Q1 may need to be

significantly lower than that for Q2. These conditions can

often be met by paralleling two MOSFETs for Q1 and using

a single device for Q2. Note that using a higher PMAX value

Table 4. Recommended MOSFETs for LTC1753 Applications

PARTS

Siliconix SUD50N03-10

D-PAK

Siliconix Si4410DY

SO-8

ON Semiconductor MTD20N03HDL

D PAK

Fairchild FDS6670A

SO-8

Fairchild FDS6680

SO-8

ON Semiconductor MTB75N03HDL

DD PAK

IR IRL3103S

DD PAK

IR IRLZ44

TO-220

Fuji 2SK1388

TO-220

RDS(ON)

AT 25°C (mΩ)

19

20

35

8

10

7.5

14

28

37

RATED CURRENT (A)

15 at 25°C

10 at 100°C

10 at 25°C

8 at 75°C

20 at 25°C

16 at 100°C

13 at 25°C

11.5 at 25°C

75 at 25°C

59 at 100°C

56 at 25°C

40 at 100°C

50 at 25°C

36 at 100°C

35 at 25°C

Note: Please refer to the manufacturer’s data sheet for testing conditions

and detail information.

TYPICAL INPUT

CAPACITANCE

CISS (pF)

3200

2700

880

3200

2070

4025

1600

3300

1750

θJC (°C/W)

1.8

—

1.67

25

25

1.0

1.8

1.0

2.08

TJMAX (°C)

175

150

150

150

150

150

175

175

150

14

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