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RT9715DGBR Datasheet(PDF) 9 Page - Richtek Technology Corporation |
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RT9715DGBR Datasheet(HTML) 9 Page - Richtek Technology Corporation |
9 / 15 page RT9715 9 DS9715-03 April 2011 www.richtek.com Power Dissipation The junction temperature of the RT9715 series depend on several factors such as the load, PCB layout, ambient temperature and package type. The output pin of the RT9715 can deliver the current of up to 2A (RT9715A/B), 1.5A(RT9715C/D), 1.1A(RT9715E/F) and 0.7A(RT9715G/ H) 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 the switch as below. PD = RDS(ON) x IOUT2 Although the devices are rated for 2A, 1.5A, 1.1A and 0.7A 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 junction temperature of the die (100 °C)andTA is the maximum ambient temperature. turns the pass element off. The pass element turn on again after the junction temperature cools to 80 °C. The RT9715 lowers its OTP trip level from 120 °C to 100°C when output short circuit occurs (VOUT < 1V) as shown in Figure 1. The junction to ambient thermal resistance ( θJA) for SOT-23-5/TSOT-23-5, SOP-8/MSOP-8 and WDFM-8L 3x3 packages at recommended minimum footprint are 250 °C/ W, 160 °C/W and 108°C/W respectively (θJA is layout dependent). Universal Serial Bus (USB) & Power Distribution The goal of USB is to enable 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 implementation. 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. A Bus-Powered Hub draws all of the power to any internal functions and downstream ports from the USB connector power pins. The hub may draw up to 500mA from the upstream device. External ports in a Bus-Powered Hub can supply up to 100mA per port, with a maximum of four external ports. Self-Powered Hub power for the internal functions and downstream ports does not come from the USB, although the USB interface may draw up to 100mA from its upstream connect, to allow the interface to function when the remainder of the hub is powered down. The hub must be able to supply up to 500mA on all of its external downstream ports. Please refer to Universal Serial Specification Revision 2.0 for more details on designing compliant USB hub and host systems. Over-Current protection devices such as fuses and PTC resistors (also called polyfuse or polyswitch) have slow trip times, high on-resistance, and lack the necessary circuitry for USB-required fault reporting. Figure 1. Short Circuit Thermal Folded Back Protection when Output Short Circuit Occurs (Patent) VOUT Short to GND 1V VOUT IOUT Thermal Shutdown OTP Trip Point 120 C ° 100 C ° 100 C ° 80 C ° IC Temperature |
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