LM2832YMY/NOPB National Semiconductor, LM2832YMY/NOPB Datasheet - Page 15

• Manufacturer Part Number: LM2832YMY/NOPB
• Description: IC REGULATOR BUCK 2A 8-EMSOP
• Manufacturer: National Semiconductor
• Type: Step-Down (Buck)r

Specifications of LM2832YMY/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 4.5 V
• Current - Output: 2A
• Frequency - Switching: 550kHz
• Voltage - Input: 3 ~ 5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP Exposed Pad, 8-HMSOP, 8-eMSOP
• For Use With: LM2832YMY EVAL - BOARD EVAL LM2832YMY
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: *LM2832YMY/NOPB; LM2832YMY; LM2832YMYTR

Thermal Definitions
Thermal impedance from the silicon junction to the ambient
air is defined as:
The PCB size, weight of copper used to route traces and
ground plane, and number of layers within the PCB can
greatly effect R
also make a large difference in the thermal impedance.
Thermal vias are necessary in most applications. They con-
duct heat from the surface of the PCB to the ground plane.
Four to six thermal vias should be placed under the exposed
pad to the ground plane if the LLP package is used.
Thermal impedance also depends on the thermal properties
of the application operating conditions (Vin, Vo, Io etc), and
the surrounding circuitry.
Silicon Junction Temperature Determination Method 1:
To accurately measure the silicon temperature for a given
application, two methods can be used. The first method
requires the user to know the thermal impedance of the
silicon junction to top case temperature.
Some clarification needs to be made before we go any
further.
R
package to silicon junction.
R
junction.
In this data sheet we will use R
to measure top case temperature with a small thermocouple
attached to the top case.
R
with the exposed pad. Knowing the internal dissipation from
the efficiency calculation given previously, and the case
temperature, which can be empirically measured on the
bench we have:
Therefore:
From the previous example:
The second method can give a very accurate silicon junction
temperature.
The first step is to determine R
LM2832 has over-temperature protection circuitry. When the
silicon temperature reaches 165˚C, the device stops switch-
ing. The protection circuitry has a hysteresis of about 15˚C.
Once the silicon temperature has decreased to approxi-
mately 150˚C, the device will start to switch again. Knowing
this, the R
the early stages of the design one may calculate the R
placing the PCB circuit into a thermal chamber. Raise the
θJC
ΦJC
ΦJC
is the thermal impedance from all six sides of an IC
is the thermal impedance from top case to the silicon
is approximately 30˚C/Watt for the 6-pin LLP package
θJA
for any application can be characterized during
θJA
T
T
j
T
j
= (R
. The type and number of thermal vias can
= 30˚C/W x 0.339W + T
j
= (R
ΦJC
ΦJC
x P
x P
INTERNAL
ΦJC
LOSS
θJA
so that it allows the user
(Continued)
) + T
of the application. The
) + T
C
C
C
θJA
by
15
ambient temperature in the given working application until
the circuit enters thermal shutdown. If the SW-pin is moni-
tored, it will be obvious when the internal PFET stops switch-
ing, indicating a junction temperature of 165˚C. Knowing the
internal power dissipation from the above methods, the junc-
tion temperature, and the ambient temperature R
determined.
Once this is determined, the maximum ambient temperature
allowed for a desired junction temperature can be found.
An example of calculating R
National Semiconductor LM2832 LLP demonstration board
is shown below.
The four layer PCB is constructed using FR4 with
copper traces. The copper ground plane is on the bottom
layer. The ground plane is accessed by two vias. The board
measures 3.0cm x 3.0cm. It was placed in an oven with no
forced airflow. The ambient temperature was raised to
126˚C, and at that temperature, the device went into thermal
shutdown.
From the previous example:
If the junction temperature was to be kept below 125˚C, then
the ambient temperature could not go above 86˚C.
LLP Package
For certain high power applications, the PCB land may be
modified to a "dog bone" shape (see Figure 6). By increasing
the size of ground plane, and adding thermal vias, the R
for the application can be reduced.
FIGURE 4. Internal LLP Connection
125˚C - (115˚C/W x 339mW) = 86˚C
T
j
P
- (R
INTERNAL
θJA
x P
θJA
= 339mW
LOSS
for an application using the
) = T
A
www.national.com
θJA
20197568
can be
1
⁄
2
θJA
oz