MC33765DTBR2 View Datasheet(PDF) - ON Semiconductor

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Description

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MC33765DTBR2

Very Low Dropout/Ultra Low Noise 5 Outputs Voltage Regulator

ON Semiconductor 

MC33765

DEFINITIONS

Load Regulation − The change in output voltage for a

change in load current at constant chip temperature.

Dropout Voltage − The input/output differential at which

the regulator output no longer maintains regulation against

further reductions in input voltage. Measured when the

output drops 100 mV below its nominal value (which is

measured at 1.0 V differential input/output), dropout voltage

is affected by junction temperature, load current and

minimum input supply requirements.

Output Noise Voltage − The RMS AC voltage at the

output with a constant load and no input ripple, measured

over a specified frequency range.

MC33765 Output noise performances

300

Vin = 3.6V

250

Iout = typical

Cbyp = 10nF

As the device can be switched ON/OFF through

independent Enable (ON/OFF pin) or Common Enable, the

output signal could be, for example, a square wave. Let’s

assume that the device is ON during TON on a signal period

T. The RMS current will be given by:

IoutRMS + IP ǸD

where

D

+

TON

T

Ton

Ip

200

150

OUT1, 2, 3, 4, 5

100

50

OUT3

0

10

100

1000

10000 100000 1000000

Frequency (Hz)

Maximum Power Dissipation − The maximum total

dissipation for which the regulator will operate within

specifications.

Quiescent Current − Current which is used to operate the

regulator chip with no load current.

Line Regulation − The change in input voltage for a

change in the input voltage. The measurement is made under

conditions of low dissipation or by using pulse techniques

such that the average chip temperature is not significantly

affected.

Thermal Protection − Internal thermal shutdown

circuitry is provided to protect the integrated circuit in the

event that the maximum junction temperature is exceeded.

When activated, typically 160°C, the regulator turns off.

This feature is provided to prevent catastrophic failures from

accidental overheating.

Maximum Package Power Dissipation and RMS

Current − The maximum package power dissipation is the

power dissipation level at which the junction temperature

reaches its maximum value i.e. 125°C. The junction

temperature is rising while the difference between the input

power (VCC X ICC) and the output power (Vout X Iout) is

increasing.

As MC33765 device exhibits five independent outputs

Iout is specified as the maximum RMS current combination

of the five output currents.

T, period

Depending on ambient temperature, it is possible to

calculate the maximum power dissipation and so the

maximum RMS current as following:

Pd

+

TJ – TA

RqJA

The maximum operating junction temperature TJ is

specified at 125°C, if TA = 25°C, then PD = 700 mW. By

neglecting the quiescent current, the maximum power

dissipation can be expressed as:

Iout

+

PD

VCC –

Vout

So that in the more drastic conditions:

VCC = 5.3 V, Vout = 2.7 V then the maximum RMS value of

Iout is 269 mA.

The maximum power dissipation supported by the device

is a lot increased when using appropriate application design.

Mounting pad configuration on the PCB, the board material

and also the ambient temperature are affected the rate of

temperature rise. It means that when the IC has good thermal

conductivity through PCB, the junction temperature will be

“low” even if the power dissipation is great.

The thermal resistance of the whole circuit can be

evaluated by deliberately activating the thermal shutdown

of the circuit (by increasing the output current or raising the

input voltage for example).

Then you can calculate the power dissipation by subtracting

the output power from the input power. All variables are then

well known: power dissipation, thermal shutdown temperature

(160°C for MC33765) and ambient temperature.

RqJA

+

TJ – TA

PD

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