RT9711GS datasheet(11/15 Pages) RICHTEK

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RT9711

Preliminary

DS9711-04 March 2007

www.richtek.com

Thermal Shutdown

Thermal shutdown is employed to protect the device from

damage if the die temperature exceeds approximately

130

°C. The power switch will auto-recover when the IC is

coolng down. The thermal hysteresis temperature is about

°C.

Power Dissipation

The device’ s junction temperature depends on several

factors such as the load, PCB layout, ambient temperature

and package type. The output pin of RT9711 can deliver a

current up to 1.5A, respectively over the full operating

junction temperature range. However, the maximum output

current must be derated at higher ambient temperature to

ensure the junction temperature does not exceed 125

°C.

With all possible conditions, the junction temperature must

be within the range specified under operating conditions.

Power dissipation can be calculated based on the output

current and the RDS(ON) of switch as below.

PD = RDS(ON) x (IOUT)

Although the devices are rated for 1.5A of output current,

but the application may limit the amount of output current

based on the total power dissipation and the ambient

temperature. The final operating junction temperature for

any set of conditions can be estimated by the following

thermal equation :

PD (MAX) = ( TJ(MAX)

− TA ) / θJA

Where TJ(MAX) is the maximum operation junction

temperature 125

°C, TAis the ambient temperature and the

θJA is the junction to ambient thermal resistance.

The junction to ambient thermal resistance

θJA is layout

dependent. For SOT-23-5 packages, the thermal

resistance

θJA is 250°C/W on the standard JEDEC 51-3

single-layer thermal test board.

And for SOP-8 packages, the thermal resistance

θJA is

160

°C/W. The maximum power dissipation at TA = 25°C

can be calculated by following formula :

PD(MAX) = ( 125

°C − 25°C) / 250°C/W = 0.4 W for

SOT-23-5 packages

Once this current limit threshold is exceeded the device

enters constant current mode until the thermal shutdown

occurs or the fault is removed.

Universal Serial Bus (USB) & Power Distribution

The goal of USB is to enable devices from different vendors

to interoperate in an open architecture. USB features

include ease of use for the end user, a wide range of

workloads and applications, robustness, synergy with the

PC industry, and low-cost implement- ation. Benefits

include self-identifying peripherals, dynamically attachable

and reconfigurable peripherals, multiple connections

(support for concurrent operation of many devices), support

for as many as 127 physical devices, and compatibility

with PC Plug-and-Play architecture.

The Universal Serial Bus connects USB devices with a

USB host: each USB system has one USB host. USB

devices are classified either as hubs, which provide

additional attachment points to the USB, or as functions,

which provide capabilities to the system (for example, a

digital joystick). Hub devices are then classified as either

Bus-Power Hubs or Self-Powered Hubs.

PD(MAX) = ( 125

°C − 25°C) / 160°C/W = 0.625 W for

SOP-8 packages

The maximum power dissipation depends on operating

ambient temperature for fixed TJ(MAX) and thermal

resistance

θJA. For RT9711 packages, the Figure 1 of

derating curves allows the designer to see the effect of

rising ambient temperature on the maximum power

allowed.

Figure 1. Derating Curves for RT8008 Package

0.1

0.2

0.3

0.4

0.5

0.6

0.7

100

125

Ambient Temperature

Single Layer PCB

(

°C)

SOP-8

SOT-23-5

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