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LT3050MPMSE#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P26
LT3050 Series
19
3050fa
APPLICATIONS INFORMATION
DC BIAS VOLTAGE (V)
CHANGE IN VALUE (%)
3050 F04
20
0
–20
–40
–60
–80
–100
0
4
8
10
26
12
14
X5R
Y5V
16
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
TEMPERATURE (°C)
–50
40
20
0
–20
–40
–60
–80
–100
25 75
3050 F05
–25 0
50 100 125
Y5V
CHANGE IN VALUE (%)
X5R
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
Figure 4. Ceramic Capacitor DC Bias Characteristics
Figure 5. Ceramic Capacitor Temperature Characteristics
Start-up time is also affected by the presence of a feed-
forward capacitor. Start-up time is directly proportional to
the size of the feedforward capacitor and the output volt-
age, and is inversely proportional to the feedback resistor
divider current, slowing to 15ms with a 4.7nF feedforward
capacitor and a 10µF output capacitor for an output voltage
set to 5V by a 5µA feedback resistor divider.
Output Capacitance
The LT3050 regulator is stable with a wide range of output
capacitors. The ESR of the output capacitor affects stability,
most notably with small capacitors. Use a minimum output
capacitor of 2.2µF with an ESR of 3 or less to prevent
oscillations. If a feedforward capacitor is used with output
voltages set for greater than 24V, use a minimum output
capacitor of 4.7µF. The LT3050 is a micropower device
and output load transient response is a function of output
capacitance. Larger values of output capacitance decrease
the peak deviations and provide improved transient re-
sponse for larger load current changes. Bypass capacitors,
used to decouple individual components powered by the
LT3050, increase the effective output capacitor value. For
applications with large load current transients, a low ESR
ceramic capacitor in parallel with a bulk tantalum capacitor
often provides an optimally damped response.
Give extra consideration to the use of ceramic capacitors.
Manufacturers make ceramic capacitors with a variety of
dielectrics, each with different behavior across tempera-
ture and applied voltage. The most common dielectrics
are specifi ed with EIA temperature characteristic codes
of Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics
provide high C-V products in a small package at low cost,
but exhibit strong voltage and temperature coeffi cients, as
shown in Figures 4 and 5. When used with a 5V regulator,
a 16V 10F Y5V capacitor can exhibit an effective value
as low as 1F to 2F for the DC bias voltage applied, and
over the operating temperature range. The X5R and X7R
dielectrics yield much more stable characteristics and are
more suitable for use as the output capacitor.
The X7R type works over a wider temperature range and
has better temperature stability, while the X5R is less
expensive and is available in higher values. Care still must
be exercised when using X5R and X7R capacitors; the X5R
and X7R codes only specify operating temperature range
and maximum capacitance change over temperature.
Capacitance change due to DC bias with X5R and X7R
capacitors is better than Y5V and Z5U capacitors, but can
still be signifi cant enough to drop capacitor values below
appropriate levels. Capacitor DC bias characteristics tend
to improve as component case size increases, but expected
capacitance at operating voltage should be verifi ed.
LT3050 Series
20
3050fa
Figure 6. Noise Resulting from Tapping on a Ceramic Capacitor
10ms/DIV
V
OUT
1mV/DIV
3050 F06
V
OUT
= 5V
C
OUT
= 10µF
C
REF/BYP
= 10nF
APPLICATIONS INFORMATION
Voltage and temperature coeffi cients are not the only
sources of problems. Some ceramic capacitors have a
piezoelectric response. A piezoelectric device generates
voltage across its terminals due to mechanical stress,
similar to the way a piezoelectric accelerometer or micro-
phone works. For a ceramic capacitor, the stress is induced
by vibrations in the system or thermal transients. The
resulting voltages produced cause appreciable amounts
of noise. A ceramic capacitor produced the trace in
Figure 6 in response to light tapping from a pencil. Similar
vibration induced behavior can masquerade as increased
output voltage noise.
Overload Recovery
Like many IC power regulators, the LT3050 has safe oper-
ating area protection. The safe area protection decreases
current limit as input-to-output voltage increases, and
keeps the power transistor inside a safe operating region
for all values of input-to-output voltage. The LT3050 pro-
vides some output current at all values of input-to-output
voltage up to the device breakdown.
When power is fi rst applied, the input voltage rises and the
output follows the input; allowing the regulator to start-up
into very heavy loads. During start-up, as the input voltage
is rising, the input-to-output voltage differential is small,
allowing the regulator to supply large output currents.
With a high input voltage, a problem can occur wherein
the removal of an output short will not allow the output
to recover. Other regulators, such as the LT1083/LT1084/
LT1085 family and LT1764A also exhibit this phenomenon,
so it is not unique to the LT3050. The problem occurs with
a heavy output load when the input voltage is high and the
output voltage is low. Common situations are: immediately
after the removal of a short-circuit or if the shutdown pin
is pulled high after the input voltage is already turned on.
The load line for such a load intersects the output cur-
rent curve at two points. If this happens, there are two
stable output operating points for the regulator. With this
double intersection, the input power supply needs to be
cycled down to zero and brought up again to make the
output recover.
Thermal Considerations
The LT3050’s maximum rated junction temperature of
125°C limits its power handling capability. Two components
comprise the power dissipated by the device:
1. Output current multiplied by the input/output
voltage differential: I
OUT
• (V
IN
– V
OUT
), and
2. GND pin current multiplied by the input voltage:
I
GND
• V
IN
GND pin current is determined using the GND Pin Current
curves in the Typical Performance Characteristics section.
Power dissipation equals the sum of the two components
listed above.
The LT3050 regulator has internal thermal limiting that
protects the device during overload conditions. For con-
tinuous normal conditions, do not exceed the maximum
junction temperature of 125°C. Carefully consider all
sources of thermal resistance from junction-to-ambient
including other heat sources mounted in proximity to the
LT3050.
The undersides of the LT3050 DFN and MSOP packages
have exposed metal from the lead frame to the die attach-
ment. These packages allow heat to directly transfer from
the die junction to the printed circuit board metal to control
maximum operating junction temperature. The dual-in-line
pin arrangement allows metal to extend beyond the ends
of the package on the topside (component side) of a PCB.
Connect this metal to GND on the PCB. The multiple IN
and OUT pins of the LT3050 also assist in spreading heat
to the PCB.
LT3050 Series
21
3050fa
APPLICATIONS INFORMATION
For surface mount devices, heat sinking is accomplished
by using the heat spreading capabilities of the PC board
and its copper traces. Copper board stiffeners and plated
through-holes also can spread the heat generated by
power devices. The following tables list thermal resis-
tance as a function of copper area in a fi xed board size.
All measurements were taken in still air on a four-layer
FR-4 board with one ounce solid internal planes and two
ounce external trace planes with a total board thickness
of 1.6mm. For further information on thermal resistance
and using thermal information, refer to JEDEC standard
JESD51, notably JESD51-12.
Table 1. MSOP Measured Thermal Resistance
COPPER AREA
BOARD
AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)TOPSIDE BACKSIDE
2500 sq mm 2500 sq mm 2500 sq mm 40°C/W
1000 sq mm 2500 sq mm 2500 sq mm 41°C/W
225 sq mm 2500 sq mm 2500 sq mm 43°C/W
100 sq mm 2500 sq mm 2500 sq mm 45°C/W
Table 2. DFN Measured Thermal Resistance
COPPER AREA
TOPSIDE BOARD AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
2500 sq mm 2500 sq mm 44°C/W
1000 sq mm 2500 sq mm 45°C/W
225 sq mm 2500 sq mm 47°C/W
100 sq mm 2500 sq mm 49°C/W
Calculating Junction Temperature
Example: Given an output voltage of 5V, an input voltage
range of 12V ±5%, a maximum output current range of
75mA and a maximum ambient temperature of 85°C, what
will the maximum junction temperature be?
The power dissipated by the device equals:
I
OUT(MAX)
* (V
IN(MAX)
– V
OUT
) + I
GND
* V
IN(MAX)
where,
I
OUT(MAX)
= 75mA
V
IN(MAX)
= 12.6V
I
GND
at (I
OUT
= 75mA, V
IN
= 12V) = 1.5mA
So,
P = 75mA • (12.6V - 5V) + 1.5mA • 12.6V = 0.589W
Using a DFN package, the thermal resistance ranges from
44°C/W to 49°C/W depending on the copper area. So the
junction temperature rise above ambient approximately
equals:
0.589W • 49°C/W = 28.86°C
The maximum junction temperature equals the maximum
ambient temperature plus the maximum junction tempera-
ture rise above ambient or:
T
JMAX
= 85°C + 28.86°C = 113.86°C
Protection Features
The LT3050 incorporates several protection features that
make it ideal for use in battery-powered circuits. In ad-
dition to the normal protection features associated with
monolithic regulators, such as current limiting and thermal
limiting, the device also protects against reverse-input
voltages, reverse-output voltages and reverse output-to-
input voltages.
Current limit protection and thermal overload protection
protect the device against current overload conditions at
the output of the device. For normal operation, do not
exceed a junction temperature of 125°C.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P26

LT3050MPMSE#TRPBF

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Manufacturer:
Analog Devices / Linear Technology
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LDO Voltage Regulators 100mA Protected Antenna Supply LDO
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