Linear Technology DC1216A-D - 100MHz PLL Synthesizer Reference Clock Source DC1216A-D DC1216A-D 데이터 시트
제품 코드
DC1216A-D
LT1761 Series
15
1761sff
APPLICATIONS INFORMATION
The LT1761 series are 100mA low dropout regulators with
micropower quiescent current and shutdown. The devices
are capable of supplying 100mA at a dropout voltage of
300mV. Output voltage noise can be lowered to 20μV
micropower quiescent current and shutdown. The devices
are capable of supplying 100mA at a dropout voltage of
300mV. Output voltage noise can be lowered to 20μV
RMS
over a 10Hz to 100kHz bandwidth with the addition of a
0.01μF reference bypass capacitor. Additionally, the refer-
ence bypass capacitor will improve transient response of
the regulator, lowering the settling time for transient load
conditions. The low operating quiescent current (20μA)
drops to less than 1μA in shutdown. In addition to the
low quiescent current, the LT1761 regulators incorporate
several protection features which make them ideal for use
in battery-powered systems. The devices are protected
against both reverse input and reverse output voltages.
In battery backup applications where the output can be
held up by a backup battery when the input is pulled to
ground, the LT1761-X acts like it has a diode in series with
its output and prevents reverse current fl ow. Additionally,
in dual supply applications where the regulator load is
returned to a negative supply, the output can be pulled
below ground by as much as 20V and still allow the device
to start and operate.
0.01μF reference bypass capacitor. Additionally, the refer-
ence bypass capacitor will improve transient response of
the regulator, lowering the settling time for transient load
conditions. The low operating quiescent current (20μA)
drops to less than 1μA in shutdown. In addition to the
low quiescent current, the LT1761 regulators incorporate
several protection features which make them ideal for use
in battery-powered systems. The devices are protected
against both reverse input and reverse output voltages.
In battery backup applications where the output can be
held up by a backup battery when the input is pulled to
ground, the LT1761-X acts like it has a diode in series with
its output and prevents reverse current fl ow. Additionally,
in dual supply applications where the regulator load is
returned to a negative supply, the output can be pulled
below ground by as much as 20V and still allow the device
to start and operate.
Adjustable Operation
The adjustable version of the LT1761 has an output voltage
range of 1.22V to 20V. The output voltage is set by the
ratio of two external resistors as shown in Figure 1. The
device servos the output to maintain the ADJ pin voltage
at 1.22V referenced to ground. The current in R1 is then
equal to 1.22V/R1 and the current in R2 is the current in
R1 plus the ADJ pin bias current. The ADJ pin bias cur-
rent, 30nA at 25°C, fl ows through R2 into the ADJ pin.
The output voltage can be calculated using the formula in
Figure 1. The value of R1 should be no greater than 250k
to minimize errors in the output voltage caused by the
range of 1.22V to 20V. The output voltage is set by the
ratio of two external resistors as shown in Figure 1. The
device servos the output to maintain the ADJ pin voltage
at 1.22V referenced to ground. The current in R1 is then
equal to 1.22V/R1 and the current in R2 is the current in
R1 plus the ADJ pin bias current. The ADJ pin bias cur-
rent, 30nA at 25°C, fl ows through R2 into the ADJ pin.
The output voltage can be calculated using the formula in
Figure 1. The value of R1 should be no greater than 250k
to minimize errors in the output voltage caused by the
ADJ pin bias current. Note that in shutdown the output is
turned off and the divider current will be zero. Curves of
ADJ Pin Voltage vs Temperature and ADJ Pin Bias Cur-
rent vs Temperature appear in the Typical Performance
Characteristics.
turned off and the divider current will be zero. Curves of
ADJ Pin Voltage vs Temperature and ADJ Pin Bias Cur-
rent vs Temperature appear in the Typical Performance
Characteristics.
The adjustable device is tested and specifi ed with the ADJ
pin tied to the OUT pin for an output voltage of 1.22V.
Specifi cations for output voltages greater than 1.22V will
be proportional to the ratio of the desired output voltage
to 1.22V: V
pin tied to the OUT pin for an output voltage of 1.22V.
Specifi cations for output voltages greater than 1.22V will
be proportional to the ratio of the desired output voltage
to 1.22V: V
OUT
/1.22V. For example, load regulation for an
output current change of 1mA to 100mA is –1mV typical
at V
at V
OUT
= 1.22V. At V
OUT
= 12V, load regulation is:
(12V/1.22V)(–1mV) = –9.8mV
Bypass Capacitance and Low Noise Performance
The LT1761 regulators may be used with the addition of a
bypass capacitor from OUT to the BYP pin to lower output
voltage noise. A good quality low leakage capacitor is rec-
ommended. This capacitor will bypass the reference of the
regulator, providing a low frequency noise pole. The noise
pole provided by this bypass capacitor will lower the output
voltage noise to as low as 20μV
bypass capacitor from OUT to the BYP pin to lower output
voltage noise. A good quality low leakage capacitor is rec-
ommended. This capacitor will bypass the reference of the
regulator, providing a low frequency noise pole. The noise
pole provided by this bypass capacitor will lower the output
voltage noise to as low as 20μV
RMS
with the addition of a
0.01μF bypass capacitor. Using a bypass capacitor has the
added benefi t of improving transient response. With no
bypass capacitor and a 10μF output capacitor, a 10mA to
100mA load step will settle to within 1% of its fi nal value
in less than 100μs. With the addition of a 0.01μF bypass
capacitor, the output will stay within 1% for a 10mA to
100mA load step (see LT1761-5 Transient Response in
Typical Performance Characteristics section). However,
regulator start-up time is proportional to the size of the
bypass capacitor, slowing to 15ms with a 0.01μF bypass
capacitor and 10μF output capacitor.
added benefi t of improving transient response. With no
bypass capacitor and a 10μF output capacitor, a 10mA to
100mA load step will settle to within 1% of its fi nal value
in less than 100μs. With the addition of a 0.01μF bypass
capacitor, the output will stay within 1% for a 10mA to
100mA load step (see LT1761-5 Transient Response in
Typical Performance Characteristics section). However,
regulator start-up time is proportional to the size of the
bypass capacitor, slowing to 15ms with a 0.01μF bypass
capacitor and 10μF output capacitor.
IN
1761 F01
R2
LT1761
OUT
V
IN
V
OUT
ADJ
GND
R1
+
V
V
R
R
I
R
V
V
I
nA
OUT
ADJ
ADJ
ADJ
¥
§
¦
´
¶
µ
o
1 22
1
2
1
2
1 22
30
AT 25 C
OUTPUT RANGE = 1.22V TO 20V
Figure 1. Adjustable Operation