RT9179 Просмотр технического описания (PDF) - Richtek Technology
Номер в каталоге
Компоненты Описание
Список матч
RT9179 Datasheet PDF : 10 Pages
| |||
RT9179
Thermal Considerations
The RT9179 can deliver a current of up to 300mA 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 voltage drop across
regulator.
PD = (VIN - VOUT) IOUT + VIN IGND
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 (125° C) and TA is the maximum ambient
temperature. The junction to ambient thermal resistance
(θJA) for SOT-23-5 package at recommended minimum
footprint is 250°C/W (θJA is layout dependent). Visit our
website in which “Recommended Footprints for Soldering
Surface Mount Packages” for detail.
PCB Layout
Good board layout practices must be used or instability
can be induced because of ground loops and voltage drops.
The input and output capacitors MUST be directly
connected to the input, output, and ground pins of the
device using traces which have no other currents flowing
through them.
The best way to do this is to layout CIN and COUT near the
device with short traces to the VIN, VOUT, and ground pins.
The regulator ground pin should be connected to the
external circuit ground so that the regulator and its
capacitors have a “single point ground”.
It should be noted that stability problems have been seen
in applications where “vias” to an internal ground plane
were used at the ground points of the device and the input
and output capacitors. This was caused by varying ground
potentials at these nodes resulting from current flowing
through the ground plane.
Using a single point ground technique for the regulator
and it's capacitors fixed the problem. Since high current
flows through the traces going into VIN and coming from
VOUT, Kelvin connect the capacitor leads to these pins so
there is no voltage drop in series with the input and output
capacitors.
Optimum performance can only be achieved when the
device is mounted on a PC board according to the diagram
below:
ADJ
VOUT
GND
GND
EN
VIN
GND
SOT-23-5 Board Layout
DS9179-08 March 2007
www.richtek.com
9
Share Link: 