TK71135NT/135 Просмотр технического описания (PDF) - Toko America Inc

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TK71135NT/135

LOW DROPOUT REGULATOR

Toko America Inc  

TK711xx

DEFINITION AND EXPLANATION OF TECHNICAL TERMS

LINE REGULATION (LINE REG)

Line regulation is the ability of the regulator to maintain a

constant output voltage as the input voltage changes.

LOAD REGULATION (LOAD REG)

Load regulation is the ability of the regulator to maintain a

constant output voltage as the load current changes. It is

a pulsed measurement to minimize temperature effects.

The load regulation is specified an output current step

condition of 1 mA to 60 mA.

QUIESCENT CURRENT (IQ)

The quiescent current is the current which flows through

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

GROUND CURRENT (IGND)

Ground current is the current which flows through the

ground pin(s). It is defined as IIN - IOUT, excluding ICONT.

DROPOUT VOLTAGE (VDROP)

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 + 1 at a chosen load current. When the

output voltage has dropped 100 mV from the nominal, VIN

- VO is the dropout voltage. This voltage is affected by load

current and junction temperature.

OUTPUT NOISE VOLTAGE

PACKAGE POWER DISSIPATION (PD)

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

temperature rise is greatly affected by the mounting pad

configuration 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 mounting pad, the power dissipation of the TO-92 is

increased to 500 mW. For operation at ambient

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

92 device should be derated at 4.0 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

dissipation 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

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

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.

For Toko ICs, the internal limit for junction temperature is

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

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 14

July 2000 TOKO, Inc.

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