TK11927MTL Просмотр технического описания (PDF) - Toko America Inc

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TK11927MTL

VOLTAGE REGULATOR WITH RESET OUTPUT

Toko America Inc  

TK119xx

DEFINITION AND EXPLANATION OF TECHNICAL TERMS

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 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.

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(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.

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 recommended 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 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:

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

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.

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:

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.

January 1999 TOKO, Inc.

Page 19

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