LT3022EMSE-1.8#PBF Linear Technology, LT3022EMSE-1.8#PBF Datasheet - Page 16

• Manufacturer Part Number: LT3022EMSE-1.8#PBF
• Description: IC, LDO REG, 1A, 1.8V, MSOP-16
• Manufacturer: Linear Technology

Specifications of LT3022EMSE-1.8#PBF

• Primary Input Voltage: 2.1V
• Output Voltage Fixed: 1.8V
• Dropout Voltage Vdo: 145mV
• No. Of Pins: 16
• Output Current: 1A
• Operating Temperature Range: -40°C To +125°C
• Peak Reflow Compatible (260 C): Yes
• Msl: MSL 1 - Unlimited
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LT3022/LT3022-1.2
LT3022-1.5/LT3022-1.8
APPLICATIONS INFORMATION
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. In the case where the input is grounded, there is
less than 1μA of reverse output current. If the LT3022 IN
pin is forced below the OUT pin or the OUT pin is pulled
above the IN pin, input current drops to less than 10μA
typically. This occurs if the LT3022 input is connected to
a discharged (low voltage) battery and either a backup
battery or a second regulator circuit holds up the output.
The state of the SHDN pin has no effect on the reverse
output current if OUT is pulled above IN.
Input Capacitance and Stability
The LT3022 design is stable with a minimum of 10μF
capacitor placed at the IN pin. Very low ESR ceramic
capacitors may be used. However, in cases where long
wires connect the power supply to the LT3022’s input and
ground, use of low value input capacitors combined with
an output load current of greater than 20mA may result
in instability. The resonant LC tank circuit formed by the
wire inductance and the input capacitor is the cause and
not a result of LT3022 instability.
The self-inductance, or isolated inductance, of a wire
is directly proportional to its length. However, the wire
diameter has less infl uence on its self inductance. For
example, the self-inductance of a 2-AWG isolated wire
with a diameter of 0.26" is about half the inductance of a
30-AWG wire with a diameter of 0.01". One foot of 30-AWG
wire has 465nH of self-inductance.
16
Several methods exist to reduce a wire’s self-inductance.
One method divides the current fl owing towards the
LT3022 between two parallel conductors. In this case,
placing the wires further apart reduces the inductance;
up to a 50% reduction when placed only a few inches
apart. Splitting the wires connects two equal inductors
in parallel. However, when placed in close proximity to
each other, mutual inductance adds to the overall self
inductance of the wires. The most effective technique to
reducing overall inductance is to place the forward and
return current conductors (the input wire and the ground
wire) in close proximity. Two 30-AWG wires separated by
0.02" reduce the overall self-inductance to about one-fi fth
of a single wire.
If a battery, mounted in close proximity, powers the LT3022,
a 10μF input capacitor suffi ces for stability. However,
if a distantly located supply powers the LT3022, use a
larger value input capacitor. Use a rough guideline of 1μF
(in addition to the 10μF minimum) per 8 inches of wire
length. The minimum input capacitance needed to stabilize
the application also varies with power supply output
impedance variations. Placing additional capacitance on
the LT3022’s output also helps. However, this requires
an order of magnitude more capacitance in comparison
with additional LT3022 input bypassing. Series resistance
between the supply and the LT3022 input also helps stabilize
the application; as little as 0.1Ω to 0.5Ω suffi ces. This
impedance dampens the LC tank circuit at the expense of
dropout voltage. A better alternative is to use higher ESR
tantalum or electrolytic capacitors at the LT3022 input in
place of ceramic capacitors.
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