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PDF LT1962EMS8-2.5 Data sheet ( Hoja de datos )
| Número de pieza | LT1962EMS8-2.5 | |
| Descripción | 300mA/ Low Noise/ Micropower LDO Regulators | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s Low Noise: 20µVRMS (10Hz to 100kHz)
s Output Current: 300mA
s Low Quiescent Current: 30µA
s Wide Input Voltage Range: 1.8V to 20V
s Low Dropout Voltage: 270mV
s Very Low Shutdown Current: < 1µA
s No Protection Diodes Needed
s Fixed Output Voltages: 2.5V, 3V, 3.3V, 5V
s Adjustable Output from 1.22V to 20V
s Stable with 3.3µF Output Capacitor
s Stable with Aluminum, Tantalum or
Ceramic Capacitors
s Reverse Battery Protection
s No Reverse Current
s Overcurrent and Overtemperature Protected
s 8-Lead MSOP Package
U
APPLICATIO S
s Cellular Phones
s Battery-Powered Systems
s Noise-Sensitive Instrumentation Systems
Final Electrical Specifications
LT1962 Series
300mA, Low Noise,
Micropower
LDO Regulators
April 2000
DESCRIPTIO
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 20µVRMS 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 pro-
tection, current limiting, thermal limiting and reverse
current protection. The parts come in fixed output volt-
ages 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
VIN
3.7V TO
20V
3.3V Low Noise Regulator
IN OUT
1µF SENSE
LT1962-3.3
SHDN BYP
+
0.01µF
3.3V AT 300mA
20µVRMS NOISE
10µF
GND
1962 TA01
400
350
300
250
200
150
100
50
0
0
Dropout Voltage
50 100 150 200 250 300
LOAD CURRENT (mA)
1962 TA02
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
1
1 page  
LT1962 Series
APPLICATIO S I FOR ATIO
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 20µVRMS
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 sev-
eral 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 re-
turned 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
IN OUT
VIN LT1962
ADJ
GND
R2 +
VOUT
R1
1962 F02
VOUT = 1.22V1+ RR21 + (IADJ)(R2)
VADJ = 1.22V
IADJ = 30nA AT 25°C
OUTPUT RANGE = 1.22V TO 20V
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: VOUT/1.22V. For example, load regulation for an
output current change of 1mA to 300mA is – 2mV typical
at VOUT = 1.22V. At VOUT = 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 VOUT 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 20µVRMS 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 capaci-
tors. 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
5
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| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LT1962EMS8-2.5.PDF ] | |
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