LT1313CS 데이터 시트보기 (PDF) - Linear Technology

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LT1313CS

Dual PCMCIA VPP Driver/Regulator

Linear Technology 

LT1313

APPLICATIONS INFORMATION

The fall time from 12V to 0V is set by the output capacitor

and an internal pull-down current source which sinks

about 30mA. This source will fully discharge a 1µF capaci-

tor in less than 1ms.

Thermal Considerations

Power dissipated by the device is the sum of two compo-

nents: output current multiplied by the input-output differ-

ential voltage: IOUT × (VIN – VOUT), and ground pin current

multiplied by supply voltage: (IGND × VIN).

The ground pin current can be found by examining the

Ground Pin Current curves in the Typical Performance

Characteristics section.

Heat sinking, for surface mounted devices, is accom-

plished by using the heat spreading capabilities of the PC

board and its copper traces.

The junction temperature of the LT1313 must be limited to

125°C to ensure proper operation. Use Table 1, in con-

junction with the typical performance graphs, to calculate

the power dissipation and die temperature for a particular

application and ensure that the die temperature does not

exceed 125°C under any operating conditions.

Table 1. 16-Pin SO Package*

COPPER AREA

TOPSIDE

BACKSIDE BOARD AREA

2500 sq mm 2500 sq mm 2500 sq mm

1000 sq mm 2500 sq mm 2500 sq mm

225 sq mm 2500 sq mm 2500 sq mm

1000 sq mm 1000 sq mm 1000 sq mm

* Device is mounted on topside.

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

120°C/ W

120°C/ W

125°C/ W

131°C/ W

Calculating Junction Temperature

Example: given an output voltage of 12V, an input supply

voltage of 14V, and an output current of 100mA (one VPP

output), and a maximum ambient temperature of 50°C,

what will the maximum junction temperature be?

Power dissipated by the device will be equal to:

IOUT × (VS – VPPOUT) + (IGND × VIN)

where,

IOUT = 100mA

VIN = 14V

IGND at (IOUT = 100mA, VIN = 14V) = 5mA

so,

PD = 100mA × (14V –12V) + (5mA × 15V) = 0.275W

Using Table 1, the thermal resistance will be in the range

of 120°C/W to 131°C/W depending upon the copper area.

So the junction temperature rise above ambient will be

less than or equal to:

0.275W × 131°C/W = 36°C

The maximum junction temperature will then be equal to

the junction temperature rise above ambient plus the

maximum ambient temperature or:

TJMAX = 50°C + 36°C = 86°C

For more detailed applications information, see the LT1312

Single PCMCIA VPP Driver/Regulator data sheet.

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