LT1460 View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LT1460 Datasheet PDF : 26 Pages
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LT1460
Applications Information
Longer Battery Life
Series references have a large advantage over older shunt
style references. Shunt references require a resistor from
the power supply to operate. This resistor must be chosen
to supply the maximum current that can ever be demanded
by the circuit being regulated. When the circuit being
controlled is not operating at this maximum current, the
shunt reference must always sink this current, resulting
in high dissipation and short battery life.
The LT1460 series reference does not require a current set-
ting resistor and can operate with any supply voltage from
VOUT + 0.9V to 20V. When the circuitry being regulated does
not demand current, the LT1460 reduces its dissipation and
battery life is extended. If the reference is not delivering load
current it dissipates only a few mW, yet the same configura-
tion can deliver 20mA of load current when demanded.
Capacitive Loads
The LT1460 is designed to be stable with capacitive loads.
With no capacitive load, the reference is ideal for fast set-
tling, applications where PC board space is a premium,
or where available capacitance is limited.
The test circuit for the LT1460-2.5 shown in Figure 1 is
used to measure the response time for various load cur-
rents and load capacitors. The 1V step from 2.5V to 1.5V
produces a current step of 1mA or 100µA for RL = 1k or
RL = 10k. Figure 2 shows the response of the reference
with no load capacitance.
The reference settles to 2.5mV (0.1%) in less than 1µs
for a 100µA pulse and to 0.1% in 1.5µs with a 1mA step.
When load capacitance is greater than 0.01µF, the refer-
ence begins to ring due to the pole formed with the output
impedance. Figure 3 shows the response of the reference
to a 1mA and 100µA load current step with a 0.01µF load
capacitor. The ringing can be greatly reduced with a DC
load as small as 200µA. With large output capacitors, ≥1µF,
VIN = 5V
CIN
0.1µF
LT1460-2.5
VOUT
RL
CL
VGEN
2.5V
1.5V
1460 F01
Figure 1. Response Time Test Circuit
the ringing can be reduced with a small resistor in series
with the reference output as shown in Figure 4. Figure 5
shows the response of the LT1460-2.5 with a RS = 2Ω and
VGEN
VOUT
VOUT
2.5V
1.5V
RL = 10k
RL = 1k
1µs/DIV
1460 F02
Figure 2. CL = 0
VGEN
VOUT
VOUT
2.5V
1.5V
RL = 10k
RL = 1k
20µs/DIV
1460 F03
Figure 3. CL = 0.01µF
VIN = 5V
CIN
0.1µF
LT1460-2.5
RS VOUT RL
CL
VGEN
2.5V
1.5V
1460 F04
Figure 4. Isolation Resistor Test Circuit
VGEN
VOUT
VOUT
2.5V
1.5V
RL = 1k
RS = 0
RL = 1k
RS = 2Ω
0.1ms/DIV
1460 F05
Figure 5. Effect of RS for CL = 1µF
1460fc
15
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