LT1312CS8 Просмотр технического описания (PDF) - Linear Technology

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Компоненты Описание

производитель

LT1312CS8

Single PCMCIA VPP Driver/Regulator

Linear Technology 

LT1312

APPLICATIONS INFORMATION

VIN

6.5V TO 18V

10

VIN

9

PDRIVE

Q1

D1

MBRS140

+ C1

68µF

R4

22Ω

C4

1000pF

D2

MBRS140

1/2 LTC1142HV

5V REG

NDRIVE

20

Q2

D3

MBRS130T3

T1

1.8T

R1

30µH*

+

SENSE+ 15

100Ω

SENSE– 14

C2

1000pF

R3

18k

Q3

VN7002

R2

100Ω

R5

0.033Ω

+

C3

220µF

EN0

EN1

VALID

*LPE-6562-A026 DALE (605) 665-9301

14V AUXILIARY SUPPLY

C5

22µF

5V

OUTPUT

VS

EN0 VPPOUT

EN1 LT1312

VALID SENSE

GND

TO CARD VPP PIN

0V, 3.3V, 5V, 12V OR HI-Z

+

1µF

FROM

CARD VCC PIN

LT1312 F1

Figure 1. Deriving 14V Power from an Auxiliary Winding on the LTC1142HV 5V Regulator

loaded without regard to the loading on the 5V output of

the LTC1142HV.

Continuous mode operation is only invoked when the

LT1312 is programmed to 12V. If the LT1312 is pro-

grammed to 0V, 3.3V or 5V, power is obtained directly

from the main power source (battery pack) through diode

D1. Again, the LT1312 output can be loaded without

regard to the loading of the main 5V output.

R4 and C4 absorb transient voltage spikes associated with

the leakage inductance inherent in T1's secondary winding

and ensure that the auxiliary supply does not exceed 20V.

Figure 2 is a graph of output voltage versus output current

for the auxiliary 14V supply shown in Figure 1. Note that

the auxiliary supply voltage is slightly higher when the 5V

output is heavily loaded. This is due to the increased

energy flowing through the main 5V inductor.

LTC1142 Auxiliary Power from the 3.3V Output

The circuit of Figure 1 can be modified for operation with

low-battery count applications (6 cell). As the input volt-

age falls, the 5V duty cycle increases to the point where

there is simply not enough time to transfer energy from the

5V primary to the auxiliary winding. For applications

where heavy 12V load currents exist in conjunction with

low input voltages (<6.5V), the auxiliary winding can be

derived from the 3.3V section instead of the 5V section of

the LTC1142. In this case, a transformer with a turns ratio

of 1:3.4 to 1:3.6 should be used in place of the 3.3V section

17

VIN = 8V

EN0 = HI

16

15

IOUT5V = 1A

14

IOUT5V = 0mA

13

12

11

0.1

1

10

100

1000

AUXILIARY OUTPUT CURRENT (mA)

LT1312 F2

Figure 2. LTC1142 Auxiliary Supply Voltage

7

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