TK11900MTL Ver la hoja de datos (PDF) - Toko America Inc

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Fabricante

TK11900MTL

ADJUSTABLE LOW DROPOUT REGULATOR

Toko America Inc  

TK11900

DEFINITION AND EXPLANATION OF TECHNICAL TERMS

QUIESCENT CURRENT (I )

Q

The quiescent current is the current which flows through the

ground terminal under no load (IOUT = 0 mA).

GROUND CURRENT (IGND)

Ground current is the current which flows through the current

pin(s). It is defined as IIN - IOUT, excluding control current.

Line Regulation (Line Reg)

Line regulation is the relationship between change in output

voltage due to a change in input voltage.

Load Regulation (Load Reg)

Load regulation is the relationship between change in output

voltage due to a change in load current.

DROP OUT VOLTAGE (V )

DROP

This is a measure of how well the regulator performs as the

input voltage decreases. The smaller the number, the

further the input voltage can decrease before regulation

problems occur. Nominal output voltage is first measured

when VIN = VOUT(TYP) + 1 at a chosen load current. When the

output voltage has dropped 100 mV from the nominal, VIN

- VOUT is the dropout voltage. This voltage is affected by

load current and junction temperature.

OUTPUT NOISE VOLTAGE

This is the effective AC voltage that occurs on the output

voltage under the condition where the input noise is low and

with a given load, filter capacitor, and frequency range.

THERMAL PROTECTION

PACKAGE POWER DISSIPATION (P )

D

This is the power dissipation level at which the thermal

sensor is activated. The IC contains an internal thermal

sensor which monitors the junction temperature. When the

junction temperature exceeds the monitor threshold of

150 °C, the IC is shut down. The junction temperature rises

as the difference between the input power (VIN x IIN) and the

output power (VOUT x IOUT) increases. The rate of tempera-

ture rise is greatly affected by the mounting pad configura-

tion on the PCB, the board material, and the ambient

temperature. When the IC mounting has good thermal

conductivity, the junction temperature will be low even if the

power dissipation is great. When mounted on the recom-

mended mounting pad, the power dissipation of the SOT-

23L is increased to 400 mW. For operation at ambient

temperatures over 25 °C, the power dissipation of the SOT-

23L device should be derated at 3.2 mW/°C. To determine

the power dissipation for shutdown when mounted, attach

the device on the actual PCB and deliberately increase the

output current (or raise the input voltage) until the thermal

protection circuit is activated. Calculate the power dissipa-

tion of the device by subtracting the output power from the

input power. These measurements should allow for the

ambient temperature of the PCB. The value obtained from

PD /(150 °C - TA) is the derating factor. The PCB mounting

pad should provide maximum thermal conductivity in order

to maintain low device temperatures. As a general rule, the

lower the temperature, the better the reliability of the device.

The thermal resistance when mounted is expressed as

follows:

Tj = 0jA x PD + TA

For Toko ICs, the internal limit for junction temperature is

150 °C. If the ambient temperature (TA) is 25 °C, then:

This is an internal feature which turns the regulator off when

the junction temperature rises above 150 °C. After the

regulator turns off, the temperature drops and the regulator

output turns back on. Under certain conditions, the output

waveform may appear to be an oscillation as the output

turns off and on and back again in succession.

150 °C = 0jA x PD + 25 °C

0jA = 125 °C / PD

PD is the value when the thermal sensor is activated. A

simple way to determine PD is to calculate VIN x IIN when the

output side is shorted. Input current gradually falls as

temperature rises. You should use the value when thermal

equilibrium is reached.

Page 6

November 2000 TOKO, Inc.

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