CAT3200/3200-5
APPLICATION INFORMATION
Ceramic Capacitors
Ceramic capacitors of different dielectric materials lose
their capacitance with higher temperature and voltage at
different rates. For example, a capacitor made of X5R or
X7R material will retain most of its capacitance from –
40°C to 85°C whereas a Z5U or Y5V style capacitor will
lose considerable capacitance over that range.
Z5U and Y5V capacitors may also have voltage coefficient
causing them to lose 60% or more of their capacitance
when the rated voltage is applied. When comparing
different capacitors it is often useful consider the amount
of achievable capacitance for a given case size rather
than discussing the specified capacitance value. For
example, over rated voltage and temperature conditions,
a 1µF, 10V, Y5V ceramic capacitor in an 0603 case may
not provide any more capacitance than a 0.22µF, 10V,
X7R available in the same 0603 case. For many
CAT3200/CAT3200-5 applications these capacitors can
be considered roughly equivalent.
The capacitor manufacturer’s data sheet should be
consulted to determine what value of capacitor is needed
to ensure the desired capacitance at all temperatures
and voltages. Below is a list of ceramic capacitor
manufacturers and how to contact them:
Capacitor
Manufacturer Web
Murata
AVX/Kemet
Vishay
Kemet
Taiyo Yuden
www.murata.com
www.avxcorp.com
www.vishay.com
www.kemet.com
www.t-yuden.com
408.986.0424
408.573.4150
The overall junction to ambient thermal resistance (θ
JA
)
for device power dissipation (P
D
) consists primarily of
two paths in series. The first path is the junction to the
case (θ
JC
) which is defined by the package style, and the
second path is case to ambient (θ
CA
) thermal resistance
which is dependent on board layout. The final operating
junction temperature for any set of conditions can be
estimated by the following thermal equation:
T
JUNC
=
T
AMB
+
P
D
(
Θ
JC
)
+
P
D
(
Θ
CA
)
=
T
AMB
+
P
D
(
Θ
JA
)
The CAT3200 in SOT23 package, when mounted on
printed circuit board with two square inches of copper
allocated for “heat spreading”, will result with an overall
θ
JA
of less than 150°C/W.
For a typical application operating from a 3.8V input
supply, the maximum power dissipation is 260mW
(100mA x 3V). This would result if a maximum junction
temperature of :
T
JUNC
= T
AMB
+ P
D
(
θ
JA
)
= 85
°
C + 0.26W (150
°
C/W)
= 85
°
C + 39
°
C = 124
°
C
Phone
814.237.1431
843.448.9411
The use of multi-layer board construction with power
planes will further enhance the overall thermal
performance. In the event of no dedicated copper area
being used for heat spreading, a multi-layer board will
typically provide the CAT3200 with an overall
θ
JA
of
200°C/W. This level of thermal conduction would allow
up to 200mW be safely dissipated within the device.
Thermal Management
For higher input voltages and maximum output current
there can be substantial power dissipation in the
CAT3200/CAT3200-5. If the junction temperature
increases to 160°C, the thermal shutdown circuitry will
automatically turn off the output.
A good thermal connection to the PC board is
recommended to reduce the chip temperature.
Connecting the GND pin (Pins 4/5 for CAT3200, Pin 2 for
CAT3200-5) to a ground plane, and maintaining a solid
ground plane under the device reduces the overall
thermal resistance.
Doc. No. 5002, Rev. E
8
CATALYST [ CATALYST SEMICONDUCTOR ]
