RT9167 Просмотр технического описания (PDF) - Richtek Technology

Номер в каталоге

Компоненты Описание

Список матч

RT9167

Low-Noise, Fixed Output Voltage, 300mA/500mA LDO Regulator

Richtek Technology 

RT9167/A

Operating Region and Power Dissipation

The maximum power dissipation of RT9167/A depends

on the thermal resistance of the case and circuit board,

the temperature difference between the die junction and

ambient air, and the rate of airflow. The power dissipation

across the device is P = IOUT (VIN - VOUT). The maximum

power dissipation is: PMAX = (TJ - TA) /θJA

where TJ - TA is the temperature difference between the

RT9167/A die junction and the surrounding environment,

θJA is the thermal resistance from the junction to the

surrounding environment. The GND pin of the RT9167/A

performs the dual function of providing an electrical

connection to ground and channeling heat away. Connect

the GND pin to ground using a large pad or ground plane.

Current Limit and Thermal Protection

T9167 includes a current limit which monitors and controls

the pass transistor's gate voltage limiting the output current

to 350mA Typ. (700mA Typ. for RT9167A). Thermal-

overload protection limits total power dissipation in the

RT9167/A. When the junction temperature exceeds

TJ = +155°C, the thermal sensor signals the shutdown

logic turning off the pass transistor and allowing the IC to

cool. The thermal sensor will turn the pass transistor on

again after the IC's junction temperature cools by 10°C,

resulting in a pulsed output during continuous thermal-

overload conditions. Thermal-overloaded protection is

designed to protect the RT9167/A in the event of fault

conditions. Do not exceed the absolute maximum junction-

temperature rating of TJ = +150°C for continuous operation.

The output can be shorted to ground for an indefinite

amount of time without damaging the part by cooperation

of current limit and thermal protection.

Thermal Considerations

Thermal protection limits power dissipation in RT9167/A.

When the operation junction temperature exceeds 165°C,

the OTP circuit starts the thermal shutdown function and

turns the pass element off. The pass element turn on again

after the junction temperature cools by 30°C.

For continuous operation, do not exceed absolute

maximum operation junction temperature 125°C. The

power dissipation definition in device is:

PD = (VIN − VOUT) x IOUT + VIN x IQ

www.richtek.com

10

The maximum power dissipation depends on the thermal

resistance of IC package, PCB layout, the rate of

surroundings airflow and temperature difference

between junction to ambient. The maximum power

dissipation can be calculated by following formula :

PD(MAX) = ( TJ(MAX) - TA ) / θJA

Where TJ(MAX) is the maximum operation junction

temperature 125°C, TA is the ambient temperature and

the θJA is the junction to ambient thermal resistance.

For recommended operating conditions specification of

RT9167/A, where TJ(MAX) is the maximum junction

temperature of the die (125°C) and TA is the operated

ambient temperature. The junction to ambient thermal

resistance θJA is layout dependent. For SOT-23-5 package,

the thermal resistance θJA is 250°C/W on the standard

JEDEC 51-3 single-layer thermal test board. The maximum

power dissipation at TA = 25°C can be calculated by

following formula :

PD(MAX) = (125°C − 25°C) / 250 = 0.4W for SOT-23-5

package

PD(MAX) = (125°C - 25°C) / 160 = 0.625W for SOP-8

package

The maximum power dissipation depends on operating

ambient temperature for fixed TJ(MAX) and thermal

resistance θJA. For RT9167/A packages, the Figure 5 of

derating curves allows the designer to see the effect of

rising ambient temperature on the maximum power

allowed.

700

SOP-8

600

500

SOT-23-5

400

300

200

100

0

0

20 40 60 80 100 120 140

Ambient Temperature

Figure 5. Derating Curves for RT9167/A Packages

DS9167/A-26 March 2007

Share Link: