cat6243 ON Semiconductor, cat6243 Datasheet - Page 10

• Manufacturer Part Number: cat6243
• Description: 1 Amp Adjustable Cmos Ldo Voltage Regulator
• Manufacturer: ON Semiconductor

Input Decoupling (C
should be connected close to the CAT6243’s package.
Higher capacitance and lower ESR will improve the overall
line and load transient response.
Output Decoupling (C
be augmented to fulfill stringent load transient
requirements. The regulator works with ceramic chip
capacitors as well as tantalum devices. Larger values
improve noise rejection and load regulation transient
response. The CAT6243 is a highly stable regulator and
performs well over a wide range capacitor Equivalent Series
Resistances (ESR).
No−Load Regulation Considerations
under conditions where the only load current is through the
resistor divider that sets the output voltage. However, in the
case where the CAT6243 is configured to provide a 0.8 V
output, there is no resistor divider and the ADJ pin is
connected to VOUT. If the part is enabled under no−load
conditions, leakage current through the pass transistor at
junction temperatures above 85°C can approach several
microamperes,
approaches 150°C. If this leakage current is not directed into
a load, the output voltage will rise above nominal until a load
is applied. For this reason it is recommended that a minimum
load of 100 mA be present at all times. Normally the voltage
setting resistor divider will serve this function but if no
divider is used (VOUT = 0.8 V) then an external load of
8 KW should be provided.
Output Voltage Adjust
using resistors between the output and the ADJ input. The
output voltage and resistors are chosen using Equation 1 and
Equation 2.
A ceramic or tantalum 1 mF capacitor is recommended and
The minimum output decoupling value is 2.2 mF and can
The CAT6243 adjustable regulator will operate properly
The output voltage can be adjusted from 0.8 V to 5.0 V
V
R
R
OUT
2
1
^
^ R
+ 0.8 1 )
0.8 V
I
DIV
2
especially
V
0.8 V
OUT
IN
)
OUT
* 1
R
R
1
2
)
) I
as
ADJ
junction
R
1
APPLICATIONS INFORMATION
temperature
http://onsemi.com
(eq. 1)
(eq. 2)
(eq. 3)
10
ignored (I
recommended I
load on V
regulation. This then sets R2’s value using Equation 2 to
5 KW, which minimizes output noise. Use Equation 3 to find
the required value for R1.
Thermal Considerations
necessary to provide thermal relief. The maximum power
dissipation supported by this device is dependent upon
board design and layout. Mounting pad configuration on the
PCB, the board material, and the ambient temperature affect
the rate of junction temperature rise for the part. When the
CAT6243 has good thermal conductivity through the PCB,
the junction temperature will be relatively low even with
high power applications. The maximum dissipation the
CAT6243 can handle is given by:
CAT6243 soldered to 645 mm
FR4 PCB material can dissipate in excess of 1 W when the
ambient temperature (T
pad in the center of the package is soldered to the dissipating
copper foil. See Figure below for R
heat dissipating areas smaller than 645 mm
dissipation can be calculated from the following equations:
or
Input bias current, I
As power in the CAT6243 increases, it may become
Since T
Figure 18. Adjustable Output Resistor Divider
V
P
VIN
C
IN(MAX)
D
IN
[ V
J
OUT
is not recommended to exceed 125°C, then with
ADJ
IN
C
[
I
(I
BYP
OUT
divider
P
GND
P
= 0). Considering that the lowest
D(MAX)
D(MAX)
VIN
ENABLE
BYP
value is 100 mA then when there is no
) I
must = 100 mA to keep CAT6243 in
ADJ
CAT6243
A
I
OUT
OUT
) is 25°C. Note that this assumes the
+
GND
) (V
, for all practical designs can be
) ) I
T
) I
VOUT
2
J(MAX)
ADJ
OUT
(1 sq inch), 1 oz copper area,
GND
R
OUT
qJA
qJA
* T
(V
I
OUT
versus PCB area for
IN
R
R
A
* V
)
1
2
OUT
VOUT
C
OUT
2
)
. Power
(eq. 4)
(eq. 5)
(eq. 6)