Datasheet LT1962EMS8-5, LT1962EMS8-3, LT1962EMS8-2.5, LT1962EMS8 Datasheet (Linear Technology)
Page 1
1
LT1962 Series
300mA, Low Noise,
Micropower
LDO Regulators
April 2000
■
Low Noise: 20µV
RMS
(10Hz to 100kHz)
■
Output Current: 300mA
■
Low Quiescent Current: 30µA
■
Wide Input Voltage Range: 1.8V to 20V
■
Low Dropout Voltage: 270mV
■
Very Low Shutdown Current: < 1µA
■
No Protection Diodes Needed
■
Fixed Output Voltages: 2.5V, 3V, 3.3V, 5V
■
Adjustable Output from 1.22V to 20V
■
Stable with 3.3µF Output Capacitor
■
Stable with Aluminum, Tantalum or
Ceramic Capacitors
■
Reverse Battery Protection
■
No Reverse Current
■
Overcurrent and Overtemperature Protected
■
8-Lead MSOP Package
The LT®1962 series are micropower, low noise, low
dropout regulators. The devices are capable of supplying
300mA of output current with a dropout voltage of 300mV.
Designed for use in battery-powered systems, the low
30µA quiescent current makes them an ideal choice.
Quiescent current is well controlled; it does not rise in
dropout as it does with many other regulators.
A key feature of the LT1962 regulators is low output noise.
With the addition of an external 0.01µF bypass capacitor,
output noise drops to 20µV
RMS
over a 10Hz to 100kHz
bandwidth. The LT1962 regulators are stable with output
capacitors as low as 3.3µF. Small ceramic capacitors can
be used without the series resistance required by other
regulators.
Internal protection circuitry includes reverse battery protection, current limiting, thermal limiting and reverse
current protection. The parts come in fixed output voltages of 2.5V, 3V, 3.3V and 5V, and as an adjustable device
with a 1.22V reference voltage. The LT1962 regulators are
available in the 8-lead MSOP package.
3.3V Low Noise Regulator
■
Cellular Phones
■
Battery-Powered Systems
■
Noise-Sensitive Instrumentation Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
IN
SHDN
0.01µF
10µF
1962 TA01
OUT
SENSE
V
IN
3.7V TO
20V
BYP
GND
LT1962-3.3
3.3V AT 300mA
20µV
RMS
NOISE
1µF
+
DESCRIPTIO
U
FEATURES
APPLICATIO S
U
TYPICAL APPLICATIO
U
Final Electrical Specifications
LOAD CURRENT (mA)
0
DROPOUT VOLTAGE (mV)
400
350
300
250
200
150
100
50
0
1962 TA02
100
200
30050
150
250
Dropout Voltage
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
Page 2
2
LT1962 Series
(Note 1)
IN Pin Voltage........................................................ ±20V
OUT Pin Voltage .................................................... ±20V
Input to Output Differential Voltage (Note 2) ......... ±20V
SENSE Pin Voltage ............................................... ±20V
ADJ Pin Voltage ...................................................... ±7V
BYP Pin Voltage....................................................±0.6V
SHDN Pin Voltage................................................. ±20V
Output Short-Circut Duration.......................... Indefinite
Operating Junction Temperature Range
(Note 3) ............................................ –40°C to 125°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)..................300°C
Consult factory for Industrial and Military grade parts.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Operating Voltage I
LOAD
= 300mA ● 1.8 2.3 V
Regulated Output Voltage LT1962-2.5 VIN = 3V, I
LOAD
= 1mA 2.475 2.500 2.525 V
(Note 5) 3.5V < V
IN
< 20V, 1mA < I
LOAD
< 300mA ● 2.435 2.500 2.565 V
LT1962-3 VIN = 3.5V, I
LOAD
= 1mA 2.970 3.000 3.030 V
4V < V
IN
< 20V, 1mA < I
LOAD
< 300mA ● 2.925 3.000 3.075 V
LT1962-3.3 VIN = 3.8V, I
LOAD
= 1mA 3.267 3.300 3.333 V
4.3V < V
IN
< 20V, 1mA < I
LOAD
< 300mA ● 3.220 3.300 3.380 V
LT1962-5 VIN = 5.5V, I
LOAD
= 1mA 4.950 5.000 5.050 V
6V < V
IN
< 20V, 1mA < I
LOAD
< 300mA ● 4.875 5.000 5.125 V
ADJ Pin Voltage LT1962 VIN = 2V, I
LOAD
= 1mA 1.208 1.220 1.232 V
(Notes 4, 5) 2.3V < V
IN
< 20V, 1mA < I
LOAD
< 300mA ● 1.190 1.220 1.250 V
Line Regulation LT1962-2.5 ∆VIN = 3V to 20V, I
LOAD
= 1mA ● 15 mV
LT1962-3 ∆V
IN
= 3.5V to 20V, I
LOAD
= 1mA ● 15 mV
LT1962-3.3 ∆V
IN
= 3.8V to 20V, I
LOAD
= 1mA ● 15 mV
LT1962-5 ∆V
IN
= 5.5V to 20V, I
LOAD
= 1mA ● 15 mV
LT1962 (Note 4) ∆V
IN
= 2V to 20V, I
LOAD
= 1mA ● 15 mV
Load Regulation LT1962-2.5 VIN = 3.5V, ∆I
LOAD
= 1mA to 300mA 5 12 mV
V
IN
= 3.5V, ∆I
LOAD
= 1mA to 300mA ● 25 mV
LT1962-3 VIN = 4V, ∆I
LOAD
= 1mA to 300mA 7 15 mV
V
IN
= 4V, ∆I
LOAD
= 1mA to 300mA ● 30 mV
LT1962-3.3 VIN = 4.3V, ∆I
LOAD
= 1mA to 300mA 7 17 mV
V
IN
= 4.3V, ∆I
LOAD
= 1mA to 300mA ● 33 mV
LT1962-5 VIN = 6V, ∆I
LOAD
= 1mA to 300mA 12 25 mV
V
IN
= 6V, ∆I
LOAD
= 1mA to 300mA ● 50 mV
LT1962 (Note 4) VIN = 2.3V, ∆I
LOAD
= 1mA to 300mA 2 6 mV
V
IN
= 2.3V, ∆I
LOAD
= 1mA to 300mA ● 12 mV
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. (Note 3)
ORDER PART
NUMBER
LT1962EMS8
LT1962EMS8-2.5
LT1962EMS8-3
LT1962EMS8-3.3
LT1962EMS8-5
MS8 PART MARKING
LTML
LTPT
LTPQ
LTPS
LTPR
T
JMAX
= 150°C, θJA = 125°C/W
SEE THE APPLICATIONS
INFORMATION SECTION
FOR ADDITIONAL
INFORMATION ON
THERMAL RESISTANCE
*PIN 2: SENSE FOR LT1962-2.5/LT1962-3/
LT1962-3.3/LT1962-5. ADJ FOR LT1962
1
2
3
4
OUT
SENSE/ADJ*
BYP
GND
8
7
6
5
IN
NC
NC
SHDN
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
ELECTRICAL CHARACTERISTICS
PACKAGE/ORDER I FOR ATIO
UU
W
ABSOLUTE AXI U RATI GS
WWWU
Page 3
3
LT1962 Series
Dropout Voltage I
LOAD
= 10mA 0.10 0.15 V
V
IN
= V
OUT(NOMINAL)
I
LOAD
= 10mA ● 0.21 V
(Notes 6, 7)
I
LOAD
= 50mA 0.15 0.20 V
I
LOAD
= 50mA ● 0.28 V
I
LOAD
= 100mA 0.18 0.24 V
I
LOAD
= 100mA ● 0.33 V
I
LOAD
= 300mA 0.27 0.33 V
I
LOAD
= 300mA ● 0.43 V
GND Pin Current I
LOAD
= 0mA ● 30 75 µA
V
IN
= V
OUT(NOMINAL)
I
LOAD
= 1mA ● 65 120 µA
(Notes 6, 8)
I
LOAD
= 50mA ● 1.1 1.6 mA
I
LOAD
= 100mA ● 23 mA
I
LOAD
= 300mA ● 812 mA
Output Voltage Noise C
OUT
= 10µF, C
BYP
= 0.01µF, I
LOAD
= 300mA, BW = 10Hz to 100kHz 20 µV
RMS
ADJ Pin Bias Current (Notes 4, 9) 30 100 nA
Shutdown Threshold V
OUT
= Off to On ● 0.8 2 V
V
OUT
= On to Off ● 0.25 0.65 V
SHDN Pin Current V
SHDN
= 0V 0.01 0.5 µA
(Note 10) V
SHDN
= 20V 1 5 µA
Quiescent Current in Shutdown VIN = 6V, V
SHDN
= 0V 0.1 1 µA
Ripple Rejection VIN – V
OUT
= 1.5V (Avg), V
RIPPLE
= 0.5V
P-P
, f
RIPPLE
= 120Hz, 55 65 dB
I
LOAD
= 300mA
Current Limit VIN = 7V, V
OUT
= 0V 700 mA
V
IN
= V
OUT(NOMINAL)
+ 1V, ∆V
OUT
= –0.1V ● 320 mA
Input Reverse Leakage Current VIN = –20V, V
OUT
= 0V ● 1mA
Reverse Output Current LT1962-2.5 V
OUT
= 2.5V, VIN < 2.5V 10 20 µA
(Note 11) LT1962-3 V
OUT
= 3V, VIN < 3V 10 20 µA
LT1962-3.3 V
OUT
= 3.3V, VIN < 3.3V 10 20 µA
LT1962-5 V
OUT
= 5V, VIN < 5V 10 20 µA
LT1962 (Note 4) V
OUT
= 1.22V, VIN < 1.22V 5 10 µA
PARAMETER CONDITIONS MIN TYP MAX UNITS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. (Note 2)
Note 6: To satisfy requirements for minimum input voltage, the LT1962
(adjustable version) is tested and specified for these conditions with an
external resistor divider (two 250k resistors) for an output voltage of
2.44V. The external resistor divider will add a 5µA DC load on the output.
Note 7: Dropout voltage is the minimum input to output voltage differential
needed to maintain regulation at a specified output current. In dropout, the
output voltage will be equal to: VIN – V
DROPOUT
.
Note 8: GND pin current is tested with VIN = V
OUT(NOMINAL)
and a current
source load. This means the device is tested while operating in its dropout
region. This is the worst-case GND pin current. The GND pin current will
decrease slightly at higher input voltages.
Note 9: ADJ pin bias current flows into the ADJ pin.
Note 10: SHDN pin current flows into the SHDN pin. This current is
included in the specification for GND pin current.
Note 11: Reverse output current is tested with the IN pin grounded and the
OUT pin forced to the rated output voltage. This current flows into the OUT
pin and out the GND pin.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: Absolute maximum input to output differential voltage can not be
achieved with all combinations of rated IN pin and OUT pin voltages. With
the IN pin at 20V, the OUT pin may not be pulled below 0V. The total
measured voltage from in to out can not exceed ±20V.
Note 3: The LT1962 regulators are tested and specified under pulse load
conditions such that T
J
≈ TA. The LT1962 is 100% tested at TA = 25°C.
Performance at –40°C and 125°C is assured by design, characterization
and correlation with statistical process controls.
Note 4: The LT1962 (adjustable version) is tested and specified for these
conditions with the ADJ pin connected to the OUT pin.
Note 5: Operating conditions are limited by maximum junction
temperature. The regulated output voltage specification will not apply for
all possible combinations of input voltage and output current. When
operating at maximum input voltage, the output current range must be
limited. When operating at maximum output current, the input voltage
range must be limited.
ELECTRICAL CHARACTERISTICS
Page 4
4
LT1962 Series
reducing output voltage noise to a typical 20µV
RMS
over a
10Hz to 100kHz bandwidth. If not used, this pin must be
left unconnected.
GND (Pin 4): Ground.
SHDN (Pin 5): Shutdown. The SHDN pin is used to put the
LT1962 regulators into a low power shutdown state. The
output will be off when the SHDN pin is pulled low. The
SHDN pin can be driven either by 5V logic or opencollector logic with a pull-up resistor. The pull-up resistor
is required to supply the pull-up current of the opencollector gate, normally several microamperes, and the
SHDN pin current, typically 1µA. If unused, the SHDN pin
must be connected to VIN. The device will not function if
the SHDN pin is not connected.
NC (Pins 6, 7): No Connect. For best thermal performance, these pins are not internally connected. For improved power handling capabilities, these pins can be
connected to the PC board.
IN (Pin 8): Input. Power is supplied to the device through
the IN pin. A bypass capacitor is required on this pin if the
device is more than six inches away from the main input
filter capacitor. In general, the output impedance of a
battery rises with frequency, so it is advisable to include a
bypass capacitor in battery-powered circuits. A bypass
capacitor in the range of 1µF to 10µF is sufficient. The
LT1962 regulators are designed to withstand reverse
voltages on the IN pin with respect to ground and the OUT
pin. In the case of a reverse input, which can happen if a
battery is plugged in backwards, the device will act as if
there is a diode in series with its input. There will be no
reverse current flow into the regulator and no reverse
voltage will appear at the load. The device will protect both
itself and the load.
OUT (Pin 1): Output. The output supplies power to the
load. A minimum output capacitor of 3.3µF is required to
prevent oscillations. Larger output capacitors will be
required for applications with large transient loads to limit
peak voltage transients. See the Applications Information
section for more information on output capacitance and
reverse output characteristics.
SENSE (Pin 2): Sense. For fixed voltage versions of the
LT1962 (LT1962-2.5/LT1962-3/LT1962-3.3/LT1962-5),
the SENSE pin is the input to the error amplifier. Optimum
regulation will be obtained at the point where the SENSE
pin is connected to the OUT pin of the regulator. In critical
applications, small voltage drops are caused by the resistance (RP) of PC traces between the regulator and the load.
These may be eliminated by connecting the SENSE pin to
the output at the load as shown in Figure 1 (Kelvin Sense
Connection). Note that the voltage drop across the external PC traces will add to the dropout voltage of the
regulator. The SENSE pin bias current is 10µA at the
nominal rated output voltage. The SENSE pin can be pulled
below ground (as in a dual supply system where the
regulator load is returned to a negative supply) and still
allow the device to start and operate.
ADJ (Pin 2): Adjust. For the adjustable LT1962, this is the
input to the error amplifier. This pin is internally clamped
to ±7V. It has a bias current of 30nA which flows into the
pin. The ADJ pin voltage is 1.22V referenced to ground and
the output voltage range is 1.22V to 20V.
BYP (Pin 3): Bypass. The BYP pin is used to bypass the
reference of the LT1962 to achieve low noise performance
from the regulator. The BYP pin is clamped internally to
±0.6V (one VBE). A small capacitor from the output to this
pin will bypass the reference to lower the output voltage
noise. A maximum value of 0.01µF can be used for
Figure 1. Kelvin Sense Connection
IN
SHDN
1962 F01
R
P
OUT
V
IN
SENSE
GND
LT1962
R
P
4
2
1
5
8
+
+
LOAD
UU
U
PI FU CTIO S
Page 5
5
LT1962 Series
The LT1962 series are 300mA low dropout regulators with
micropower quiescent current and shutdown. The devices
are capable of supplying 300mA at a dropout voltage of
300mV. Output voltage noise can be lowered to 20µV
RMS
over a 10Hz to 100kHz bandwidth with the addition of a
0.01µF reference bypass capacitor. Additionally, the refer-
ence bypass capacitor will improve transient response of
the regulator, lowering the settling time for transient load
conditions. The low operating quiescent current (30µA)
drops to less than 1µA in shutdown. In addition to the low
quiescent current, the LT1962 regulators incorporate several protection features which make them ideal for use in
battery-powered systems. The devices are protected
against both reverse input and reverse output voltages. In
battery backup applications where the output can be held
up by a backup battery when the input is pulled to ground,
the LT1962-X acts like it has a diode in series with its
output and prevents reverse current flow. Additionally, in
dual supply applications where the regulator load is returned to a negative supply, the output can be pulled below
ground by as much as 20V and still allow the device to start
and operate.
Adjustable Operation
The adjustable version of the LT1962 has an output
voltage range of 1.22V to 20V. The output voltage is set by
the ratio of two external resistors as shown in Figure 2. The
device servos the output to maintain the ADJ pin voltage
at 1.22V referenced to ground. The current in R1 is then
equal to 1.22V/R1 and the current in R2 is the current in R1
plus the ADJ pin bias current. The ADJ pin bias current,
30nA at 25°C, flows through R2 into the ADJ pin. The
Figure 2. Adjustable Operation
output voltage can be calculated using the formula in
Figure 2. The value of R1 should be no greater than 250k
to minimize errors in the output voltage caused by the ADJ
pin bias current. Note that in shutdown the output is turned
off and the divider current will be zero.
The adjustable device is tested and specified with the ADJ
pin tied to the OUT pin for an output voltage of 1.22V.
Specifications for output voltages greater than 1.22V will
be proportional to the ratio of the desired output voltage to
1.22V: V
OUT
/1.22V. For example, load regulation for an
output current change of 1mA to 300mA is –2mV typical
at V
OUT
= 1.22V. At V
OUT
= 12V, load regulation is:
(12V/1.22V)(–2mV) = –19.7mV
Bypass Capacitance and Low Noise Performance
The LT1962 regulators may be used with the addition of a
bypass capacitor from V
OUT
to the BYP pin to lower output
voltage noise. A good quality low leakage capacitor is
recommended. This capacitor will bypass the reference of
the regulator, providing a low frequency noise pole. The
noise pole provided by this bypass capacitor will lower the
output voltage noise to as low as 20µV
RMS
with the
addition of a 0.01µF bypass capacitor. Using a bypass
capacitor has the added benefit of improving transient
response. With no bypass capacitor and a 10µF output
capacitor, a 10mA to 300mA load step will settle to within
1% of its final value in less than 100µs. With the addition
of a 0.01µF bypass capacitor, the output will settle to
within 1% for a 10mA to 300mA load step in less than
10µs, with total output voltage deviation of less than 2.5%.
However, regulator start-up time is inversely proportional
to the size of the bypass capacitor, slowing to 15ms with
a 0.01µF bypass capacitor and 10µF output capacitor.
Output Capacitance and Transient Response
The LT1962 regulators are designed to be stable with a
wide range of output capacitors. The ESR of the output
capacitor affects stability, most notably with small capacitors. A minimum output capacitor of 3.3µF with an ESR of
3Ω or less is recommended to prevent oscillations. The
LT1962-X is a micropower device and output transient
response will be a function of output capacitance. Larger
values of output capacitance decrease the peak deviations
IN
1962 F02
R2
OUT
V
IN
V
OUT
ADJ
GND
LT1962
R1
+
VV
R
R
IR
VV
InA
OUT ADJ
ADJ
ADJ
=+
+
()()
=
=°
122 1
2
1
2
122
30
.
.
AT 25 C
OUTPUT RANGE = 1.22V TO 20V
APPLICATIO S I FOR ATIO
WUUU
Page 6
6
LT1962 Series
and provide improved transient response for larger load
current changes. Bypass capacitors, used to decouple
individual components powered by the LT1962, will increase the effective output capacitor value. With larger
capacitors used to bypass the reference (for low noise
operation), larger values of output capacitance are needed.
For 100pF of bypass capacitance, 4.7µF of output capaci-
tor is recommended. With a 1000pF bypass capacitor or
larger, a 6.8µF output capacitor is recommended.
Extra consideration must be given to the use of ceramic
capacitors. Ceramic capacitors are manufactured with a
variety of dielectrics, each with different behavior across
temperature and applied voltage. The most common
dielectrics used are Z5U, Y5V, X5R and X7R. The Z5U and
Y5V dielectrics are good for providing high capacitance in
a small package, but exhibit strong voltage and temperature coefficients as shown in Figures 3 and 4. When used
with a 5V regulator, a 10µF Y5V capacitor can exhibit an
effective value as low as 1µF to 2µF over the operating
temperature range. The X5R and X7R dielectrics result in
more stable characteristics and are more suitable for use
as the output capacitor. The X7R type has better stability
across temperature, while the X5R is less expensive and
is available in higher values.
Voltage and temperature coefficients 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,
Figure 4. Ceramic Capacitor Temperature Characteristics
Figure 3. Ceramic Capacitor DC Bias Characteristics
DC BIAS VOLTAGE (V)
CHANGE IN VALUE (%)
1962 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
1962 F04
–25 0
50 100 125
Y5V
CHANGE IN VALUE (%)
X5R
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
similar to the way a piezoelectric accelerometer or microphone works. For a ceramic capacitor the stress can be
induced by vibrations in the system or thermal transients.
The resulting voltages produced can cause appreciable
amounts of noise, especially when a ceramic capacitor is
used for noise bypassing. A ceramic capacitor produced
Figure 5’s trace in response to light tapping from a pencil.
Similar vibration induced behavior can masquerade as
increased output voltage noise.
Figure 5. Noise Resulting from Tapping on a Ceramic Capacitor
LT1962-5
C
OUT
= 10µF
C
BYP
= 0.01µf
I
LOAD
= 100mA
V
OUT
500µV/DIV
100ms/DIV
1962 F05
Thermal Considerations
The power handling capability of the device will be limited
by the maximum rated junction temperature (125°C). The
power dissipated by the device will be made up of two
components:
APPLICATIO S I FOR ATIO
WUUU
Page 7
7
LT1962 Series
The power dissipated by the device will be equal to:
I
OUT(MAX)(VIN(MAX)
– V
OUT
) + I
GND(VIN(MAX)
)
where,
I
OUT(MAX)
= 100mA
V
IN(MAX)
= 6V
I
GND
at (I
OUT
= 100mA, VIN = 6V) = 2mA
So,
P = 100mA(6V – 3.3V) + 2mA(6V) = 0.28W
The thermal resistance will be in the range of 110°C/W to
140°C/W depending on the copper area. So the junction
temperature rise above ambient will be approximately
equal to:
0.28W(125°C/W) = 35.3°C
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
T
JMAX
= 50°C + 35.3°C = 85.3°C
Protection Features
The LT1962 regulators incorporate several protection
features which make them ideal for use in battery-powered
circuits. In addition to the normal protection features
associated with monolithic regulators, such as current
limiting and thermal limiting, the devices are protected
against reverse input voltages, reverse output voltages
and reverse voltages from output to input.
Current limit protection and thermal overload protection
are intended to protect the device against current overload
conditions at the output of the device. For normal operation, the junction temperature should not exceed 125°C.
The input of the device will withstand reverse voltages of
20V. Current flow into the device will be limited to less than
1mA (typically less than 100µA) and no negative voltage
will appear at the output. The device will protect both itself
and the load. This provides protection against batteries
which can be plugged in backward.
The output of the LT1962 can be pulled below ground
without damaging the device. If the input is left open circuit
or grounded, the output can be pulled below ground by
20V. For fixed voltage versions, the output will act like a
large resistor, typically 500k or higher, limiting current
1. Output current multiplied by the input/output voltage
differential: (I
OUT
)(VIN – V
OUT
), and
2. GND pin current multiplied by the input voltage:
(I
GND
)(VIN).
The GND pin current can be estimated using specification
in the Electrical Characteristics table. Power dissipation
will be equal to the sum of the two components listed
above.
The LT1962 series regulators have internal thermal limiting designed to protect the device during overload conditions. For continuous normal conditions, the maximum
junction temperature rating of 125°C must not be
exceeded. It is important to give careful consideration to
all sources of thermal resistance from junction to ambient.
Additional heat sources mounted nearby must also be
considered.
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 can also be used to spread the heat generated by power devices.
The following table lists thermal resistance for several
different board sizes and copper areas. All measurements
were taken in still air on 1/16" FR-4 board with one ounce
copper.
Table 1. Measured Thermal Resistance
COPPER AREA THERMAL RESISTANCE
TOPSIDE* BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT)
2500mm22500mm
2
2500mm
2
110°C/W
1000mm22500mm
2
2500mm
2
115°C/W
225mm22500mm
2
2500mm
2
120°C/W
100mm22500mm
2
2500mm
2
130°C/W
50mm22500mm
2
2500mm
2
140°C/W
*Device is mounted on topside.
Calculating Junction Temperature
Example: Given an output voltage of 3.3V, an input voltage
range of 4V to 6V, an output current range of 0mA to
100mA and a maximum ambient temperature of 50°C,
what will the maximum junction temperature be?
APPLICATIO S I FOR ATIO
WUUU
Page 8
8
LT1962 Series
flow to less than 40µA. For adjustable versions, the output
will act like an open circuit; no current will flow out of the
pin. If the input is powered by a voltage source, the output
will source the short-circuit current of the device and will
protect itself by thermal limiting. In this case, grounding
the SHDN pin will turn off the device and stop the output
from sourcing the short-circuit current.
The ADJ pin of the adjustable device can be pulled above
or below ground by as much as 7V without damaging the
device. If the input is left open circuit or grounded, the ADJ
pin will act like an open circuit when pulled below ground
and like a large resistor (typically 100k) in series with a
diode when pulled above ground.
In situations where the ADJ pin is connected to a resistor
divider that would pull the ADJ pin above its 7V clamp
voltage if the output is pulled high, the ADJ pin input
current must be limited to less than 5mA. For example, a
resistor divider is used to provide a regulated 1.5V output
from the 1.22V reference when the output is forced to 20V.
The top resistor of the resistor divider must be chosen to
limit the current into the ADJ pin to less than 5mA when the
ADJ pin is at 7V. The 13V difference between OUT and ADJ
pin divided by the 5mA maximum current into the ADJ pin
yields a minimum top resistor value of 2.6k.
In circuits where a backup battery is required, several
different input/output conditions can occur. The output
voltage may be held up while the input is either pulled to
ground, pulled to some intermediate voltage or is left open
circuit. Current flow back into the output will follow the
curve shown in Figure 6.
When the IN pin of the LT1962 is forced below the OUT pin
or the OUT pin is pulled above the IN pin, input current will
typically drop to less than 2µA. This can happen if the input
of the device is connected to a discharged (low voltage)
battery and the output is held up by either a backup battery
or a second regulator circuit. The state of the SHDN pin will
have no effect on the reverse output current when the
output is pulled above the input.
Figure 6. Reverse Output Current
1962i LT/TP 0400 4K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2000
Linear T echnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear-tech.com
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS
LT1120 125mA Low Dropout Regulator with 20µA I
Q
Includes 2.5V Reference and Comparator
LT1121 150mA Micropower Low Dropout Regulator 30µA IQ, SOT-223 Package
LT1129 700mA Micropower Low Dropout Regulator 50µA Quiescent Current
LT1175 500mA Negative Low Dropout Micropower Regulator 45µA IQ, 0.26V Dropout Voltage, SOT-223 Package
LT1521 300mA Low Dropout Micropower Regulator with Shutdown 15µA IQ, Reverse Battery Protection
LT1529 3A Low Dropout Regulator with 50µA I
Q
500mV Dropout Voltage
LTC1627 High Efficiency Synchronous Step-Down Switching Regulator Burst ModeTM Operation, Monolithic, 100% Duty Cycle
LT1761 100mA, Low Noise, Low Dropout Micropower Regulator in SOT-23 20µA Quiescent Current, 20µV
RMS
Noise
LT1762 150mA, Low Noise, LDO Micropower Regulator 25µA Quiescent Current, 20µV
RMS
Noise
LT1763 500mA, Low Noise, LDO Micropower Regulator 30µA Quiescent Current, 20µV
RMS
Noise
LT1764 3A, Fast Transient Response Low Dropout Regulator 340mV Dropout Voltage
LT1772 Constant Frequency Current Mode Step-Down DC/DC Controller Up to 94% Efficiency, SOT-23 Package, 100% Duty Cycle
LT1963 1.5A, Fast Transient Response Low Dropout Regulator SO-8, SOT-223 Packages
Burst Mode is a trademark of Linear Technology Corporation.
APPLICATIO S I FOR ATIO
WUUU
OUTPUT VOLTAGE (V)
01
REVERSE OUTPUT CURRENT (µA)
30
40
50
60
70
80
90
100
897
1962 F06
20
10
0
23
465
10
LT1962
LT1962-2.5
LT1962-3
LT1962-3.3
LT1962-5
TJ = 25°C
V
IN
= 0V
CURRENT FLOWS
INTO OUTPUT PIN
V
OUT
= V
ADJ
(LT1962)
Loading...