Datasheet

LTC1798 Series
6
1798fc
Figure 1. Reference Output Load Transient Response, 1µF Output Capacitor
10ms/DIV
V
OUT
100mV/DIV
I
OUT
1mA
0mA
1798 F01a
Longer Battery Life
Series references have an advantage over shunt style
references. To operate, shunt references require a resistor
between the power supply and the output. This resistor
must be chosen to supply the maximum current that is
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 power dissipation and short battery life.
The LTC1798 series low dropout references do not require
a current setting resistor and can operate with any supply
voltage from (V
OUT(NOMINAL
) + 0.2V) to 12.6V. When the
circuitry being regulated does not demand current, the
LTC1798 series reduces its dissipation and battery life is
extended. If the reference is not delivering load current it
BLOCK DIAGRAM
–
+
IN
6
1798 BD
2
4
OUT
3 (LTC1798)FB
2.385V
GND
R1
R2
NOTE: R1 AND R2 ARE NOT CONNECTED FOR LTC1798
0.5ms/DIV
V
OUT
100mV/DIV
I
OUT
1mA
0mA
1798 F01b
APPLICATIONS INFORMATION
dissipates only 10.8µW when operating on a 2.7V supply
for LTC1798-2.5, yet the same connection can deliver
10mA of load current when demanded.
Output Bypass Capacitor
The LTC1798 series is designed to be stable with or without
capacitive loads. With no capacitive load, the reference
is ideal for fast settling applications, or where PC board
space is at a premium.
In applications with significant output loading changes, an
output bypass capacitor of up to 1µF can be used to improve
the output transient response. Figure 1 shows the response
of the reference to a 1mA to 0µA load step with a 1µF output
capacitor. If more than 1µF of output capacitance is required,
a resistor in series with the capacitor is recommended