LM2830XMF National Semiconductor, LM2830XMF Datasheet - Page 13

• Manufacturer Part Number: LM2830XMF
• Description: BUCK REG 1A 1.6MHZ, SMD, SOT-23-5
• Manufacturer: National Semiconductor

Specifications of LM2830XMF

• Primary Input Voltage: 5.5V
• No. Of Outputs: 1
• Output Voltage: 4.5V
• Output Current: 1A
• Voltage Regulator Case Style: SOT-23
• No. Of Pins: 5
• Operating Temperature Range: -40°C To +125°C
• Svhc: No SVHC
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Calculating Efficiency, and
Junction Temperature
The complete LM2830 DC/DC converter efficiency can be
calculated in the following manner.
Or
Calculations for determining the most significant power
losses are shown below. Other losses totaling less than 2%
are not discussed.
Power loss (P
the converter: switching and conduction. Conduction losses
usually dominate at higher output loads, whereas switching
losses remain relatively fixed and dominate at lower output
loads. The first step in determining the losses is to calculate
the duty cycle (D):
V
on, and is equal to:
V
diode. It can be obtained from the diode manufactures Elec-
trical Characteristics section. If the voltage drop across the
inductor (V
The conduction losses in the free-wheeling Schottky diode
are calculated as follows:
Often this is the single most significant power loss in the
circuit. Care should be taken to choose a Schottky diode that
has a low forward voltage drop.
Another significant external power loss is the conduction
loss in the output inductor. The equation can be simplified to:
The LM2830 conduction loss is mainly associated with the
internal PFET:
If the inductor ripple current is fairly small, the conduction
losses can be simplified to:
SW
D
is the forward voltage drop across the Schottky catch
is the voltage drop across the internal PFET when it is
DCR
LOSS
) is accounted for, the equation becomes:
P
DIODE
) is the sum of two basic types of losses in
V
P
SW
IND
= V
= I
= I
OUT
OUT
D
x I
2
x R
OUT
x R
DSON
DCR
x (1-D)
13
Switching losses are also associated with the internal PFET.
They occur during the switch on and off transition periods,
where voltages and currents overlap resulting in power loss.
The simplest means to determine this loss is to empirically
measuring the rise and fall times (10% to 90%) of the switch
at the switch node.
Switching Power Loss is calculated as follows:
Another loss is the power required for operation of the inter-
nal circuitry:
I
3.3mA for the 1.6MHz frequency option.
Typical Application power losses are:
Thermal Definitions
T
T
R
R
Heat in the LM2830 due to internal power dissipation is
removed through conduction and/or convection.
Conduction: Heat transfer occurs through cross sectional
areas of material. Depending on the material, the transfer of
heat can be considered to have poor to good thermal con-
ductivity properties (insulator vs. conductor).
Heat Transfer goes as:
Silicon → package → lead frame → PCB
Convection: Heat transfer is by means of airflow. This could
be from a fan or natural convection. Natural convection
occurs when air currents rise from the hot device to cooler
air.
Thermal impedance is defined as:
Q
J
A
θJC
θJA
is the quiescent operating current, and is typically around
= Chip junction temperature
= Ambient temperature
= Thermal resistance from chip junction to ambient air
= Thermal resistance from chip junction to device case
ΣP
R
IND
ΣP
T
T
V
I
DS(ON)
COND
F
V
OUT
V
RISE
FALL
OUT
I
D
P
SW
η
P
Q
COND
IN
D
DCR
SWR
SWF
+ P
P
+ P
COND
= 1/2(V
= 1/2(V
Power Loss Tabulation
SW
P
P
1.6MHz
SWF
SW
150mΩ
INTERNAL
3.3mA
0.45V
70mΩ
0.667
5.0V
3.3V
1.0A
88%
+ P
4nS
4nS
= I
P
IN
= P
IN
Q
+ P
OUT
DIODE
= I
x I
x I
SWR
SWR
Q
2
OUT
OUT
= 125mW
x R
x V
P
+ P
+ P
P
INTERNAL
+ P
P
x F
x F
P
P
P
P
DSON
IN
P
DIODE
COND
LOSS
P
IND
SWR
SWF
OUT
IND
SWF
SW
Q
SW
Q
= P
+ P
x D
x T
x T
INTERNAL
Q
FALL
RISE
= P
150mW
100mW
345mW
125mW
17mW
70mW
3.3W
6mW
6mW
)
)
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LOSS