6

LT1460-5

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, result-

ing in high dissipation and short battery life.

The LT1460-5 series reference does not require a current

setting resistor and can operate with any supply voltage

lated does not demand current, the LT1460-5 reduces its

dissipation and battery life is extended. If the reference is

not delivering load current it dissipates less than 1mW on

a 7.5V supply, yet the same configuration can deliver

20mA of load current when demanded.

Capacitive Loads

The LT1460-5 is designed to be stable with capacitive

loads. With no capacitive load, the reference is ideal for

fast settling or applications where PC board space is a

premium. The test circuit shown in Figure 1 is used to

measure the response time for various load currents and

load capacitors. The 1V step from 5V to 4V produces a

current step of 1mA or 100

Figure 2 shows the response of the reference with no load

capacitance.

The reference settles to 5mV (0.1%) in less than 2

µs for a

100

µA pulse and to 0.1% in 3µs with a 1mA step. When

load capacitance is greater than 0.01

µF, the reference

begins to ring due to the pole formed with the output

impedance. Figure 3 shows the response of the reference

to a 1mA and 100

µA load with a 0.01µF load capacitor.

Fast Turn-On

It is recommended to add a 0.1

µF or larger input capacitor

to the input pin of the LT1460-5. This helps stability with

large load currents and speeds up turn-on. The LT1460-5

can start in 10

µs, but it is important to limit the dv/dt of the

input. Under light load conditions and with a very fast

input, internal nodes overslew and this requires finite

recovery time. Figure 4 shows the result of no bypass

LT1460-5

1460-5 F01

0.1

µF

5V

4V

Figure 1. Response Time Test Circuit

7.5V

0V

0V

20

µs/DIV

1460-5 F04

5V

4V

10

µs/DIV

1460-5 F03

5V

4V

2

µs/DIV

1460-5 F02