RT9711A データシートの表示（PDF） - Richtek Technology

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RT9711A

80mΩ, 1.5A/0.6A High-Side Power Switches with Flag

Richtek Technology 

RT9711A/B/C/D

limit threshold is exceeded the device enters constant

current mode until the thermal shutdown occurs or the

fault is removed.

Thermal Shutdown

Thermal shutdown is employed to protect the device from

damage if the die temperature exceeds approxi- mately

130°C. If enabled, the switch automatically restarts when

the die temperature falls 20°C. The output and FLG signal

will continue to cycle on and off until the device is disabled

or the fault is removed.

Power Dissipation

The junction temperature of the RT9711 series depend on

several factors such as the load, PCB layout, ambient

temperature and package type. The output pin of

RT9711A/B/C/D can deliver the current of up to 1.5A

(RT9711A/B), and 0.6A (RT9711C/D) 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 100°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 IOUT2

Although the devices are rated for 1.5A and 0.6A 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, TA is 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 and TSOT-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 and MSOP-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 = 0.4W for

SOT-23-5 and TSOT-23-5 packages

PD(MAX) = (125°C − 25°C) / 160°C/W = 0.625W for

SOP-8 and MSOP-8 packages

The maximum power dissipation depends on operating

ambient temperature for fixed TJ(MAX) and thermal

resistance θJA. For RT9711A/B/C/D packages, the Figure

1 of derating curves allows the designer to see the effect

of rising ambient temperature on the maximum power

allowed.

0.7

Single Layer PCB

0.6

SOP-8, MSOP-8

0.5

0.4

0.3

0.2

SOT-23-5, TSOT-23-5

0.1

0

0

25

50

75

100

125

Ambient Temperature (°C)

Figure 1. Derating Curves for RT9711A/B/C/D Package

Universal Serial Bus (USB) & Power Distribution

The goal of USB is to be enabled device 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

DS9711A/B/C/D-03 April 2011

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