LT1120A
8
1120afb
For more information www.linear.com/LT1120A
Figure 1. Bypassing Reference
Other than placing large capacitive loads on the reference,
no other precautions are necessary and the reference is
stable with nominal stray capacitances.
applicaTions inForMaTion
affects the transient response; low output currents have
long recovery times from load transients. At high operat-
ing temperatures the minimum load current increases and
having too low of a load current may cause the output
to go unregulated. Devices are tested for minimum load
current at high temperature. The output voltage setting
resistors to the feedback terminal can usually be used to
provide the minimum load current.
Frequency Compensation
The LT1120A is frequency compensated by a dominant
pole on the output. An output capacitor of 10µF is usu
-
ally large enough to provide good stability. Increasing
the output capacitor above 10µF further improves sta-
bility. In order to ensure stability, a feedback capacitor
is needed between the output pin and the feedback pin.
This is because stray capacitance can form another pole
with the large value of feedback resistors used with the
LT1120A. Also, a feedback capacitor minimizes noise
pickup and improves ripple rejection.
With the large dynamic operating range of the output
current, 10000:1, frequency response changes widely.
Low AC impedance capacitors are needed to insure
stability. While solid tantalum are best, aluminum elec-
trolytics can be used but larger capacitor values may be
needed.
1120A F01
20Ω
6
10µF
OUTPUT
REF
+
20Ω
6
10µF
REF
+
OUTPUTOR
Overload Protection
The main regulator in the LT1120A is current limited at
approximately 250mA. The current limit is stable with
both input voltage and temperature.
Like most other IC regulators, a minimum load is required
on the output of the LT1120A to maintain regulation. For
most standard regulators this is normally specified at
5mA. Of course, for a micropower regulator this would be
a tremendously large current. The output current must be
large enough to absorb all the leakage current of the pass
transistor at the maximum operating temperature. It also
