RT9185 RICHTEK [Richtek Technology Corporation], RT9185 Datasheet - Page 10

• Manufacturer Part Number: RT9185
• Description: Triple, Ultra-Fast CMOS LDO Regulator
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9185
P
Although the device is rated for 1.5A, 0.8A and 0.3A of
output current, 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:
P
Where T
the die (125° C) and T
temperature. θ
to the surrounding environment which is combined with
θ
which for fused SOP-8 is 20°C/W, TO-252-5 is 10°C/W
and TO-263-5 is 5.5°C/W, θ
resistance which depend on PCB board area and air flow.
PCB Layout
The RT9185 is a fixed output voltage regulator which the
voltage are sensed at the output pin. A long PCB trace to
load will cause a voltage drop between load and RT9185.
Be careful with PCB layout which minimum the output
trace length and maximum the trace width.
The GND pin of the RT9185 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.
www.richtek.com
10
JC
D
D (MAX)
= (V
+ θ
V
CA
OUT3
DD
= ( T
. Where θ
J (MAX)
) I
- V
J (MAX)
OUT3
OUT1
JA
VDD
is the maximum junction temperature of
is the thermal resistance from the junction
GND PLANE
JC
RT9185
) I
+ V
- T
OUT1
is junction to case thermal resistance
VOUT1
VOUT3
VOUT2
IN
A
GND
) / θ θ θ θ θ
I
GND
+ (V
A
CA
is the maximum ambient
JA
DD
is case to ambient thermal
TRACE RESISTANCE
DROP = I
- V
OUT2
RP
I
O
O
* RP
) I
OUT2
+ (V
LOAD
DD
-
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 C
C
and ground pins.
The regulator ground pin should be connected to the
external circuit ground so that the regulator and its
capacitors have a
It should be noted that stability problems have been seen
in applications where
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 V
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:
OUT
IN
near the device with short traces to the V
and coming from V
“
single point ground
“
vias
OUT
”
, Kelvin connect the capacitor
to an internal ground plane
DS9185-11 March 2007
”
.
DD
, V
IN
OUT
and
,