DEMO MANUAL DC368A
LT1763 500mA Low Noise
Micropower LDO Regulator
Description
Demonstration circuit DC368A is a low noise micropower
voltage regulator using the
LT
®
1763
in the 8-lead SO pack-
age. These circuits are used primarily in voltage controlled
oscillators, RF power supplies and, in larger systems, as
local regulators. The ability to tolerate a wide variety of
output capacitors makes them ideal in space- and cost-
sensitive systems.
Design files for this circuit board are available at
http://www.linear.com/demo/DC368A
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
perForMAnce sUMMArY
PARAMETER
Input Voltage Range
Output Voltage (Note 1)
Output Voltage (Note 1)
Output Voltage (Note 1)
Output Voltage (Note 1)
Output Voltage (Note 1)
Output Voltage (Note 1)
Output Voltage (Note 1)
Line Regulation
Quiescent Current
Load Regulation
SHDN Pin Threshold
Output Voltage Noise
T
A
= 25°C, V
IN
= 2.3V, V
SHDN
= 5V, I
LOAD
= 1mA, V
OUT
= 1.22V (JP2 set on Pins 1-2), unless otherwise specified.
CONDITIONS
MIN
2.3
1.208
V
IN
= 1.5V, JP2 on Pins 5-6
V
IN
= 1.8V, JP2 on Pins 7-8
V
IN
= 2.5V, JP2 on Pins 9-10
V
IN
= 3V, JP2 on Pins 11-12
V
IN
= 3.3V, JP2 on Pins 13-14
V
IN
= 5V, JP2 on Pins 15-16
∆V
IN
= 2.3V to 20V
∆I
LOAD
= 0mA
∆I
LOAD
= 1mA to 500mA
On-to-Off
Off-to-On, I
LOAD
= 1mA
I
LOAD
= 500mA, BW = 10Hz to 100kHz
0.45
1.478
1.775
2.462
2.961
3.235
4.897
1.220
1.497
1.802
2.506
3.019
3.300
5.006
1
30
0.2
0.65
0.8
20
1.8
TYP
MAX
20
1.232
1.519
1.834
2.563
3.093
3.384
5.148
5
50
1
UNITS
V
V
V
V
V
V
V
V
mV
µA
%
V
V
µV
RMS
Note 1:
Output voltage variations include ±1% tolerance of feedback divider network. For tighter voltage range, use lower tolerance resistors or use fixed
voltage output devices.
tYpicAL perForMAnce cHArActeristics
Typical Dropout Voltage
500
450
DROPOUT VOLTAGE (mV)
400
350
300
250
200
150
100
50
0
0
50 100 150 200 250 300 350 400 450 500
OUTPUT CURRENT (mA)
1763 G01
LT1763 (5V Output)
10Hz to 100kHz Output Noise
T
J
= 125C
T
J
= 25C
V
OUT
100µV/DIV
C
OUT
= 10µF
I
L
= 500mA
1ms/DIV
1763 G02
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DEMO MANUAL DC368A
pAckAge AnD scHeMAtic DiAgrAMs
LT1763CS8
TOP VIEW
OUT 1
ADJ 2
GND 3
BYP 4
8
7
6
5
IN
GND
GND
SHDN
C2
0.01µF
C3
10µF
10V
ADJ1
R1
56.2k
R2
118k
R3
261k
R4
365k
R5
422k
1.22V
USER
SELECT
1.5V
1.8V
2.5V
3V
3.3V
5V
E3
R6
768k
E4
OUT
S8 PACKAGE
8-LEAD PLASTIC SO
GND
IN
E1
C1
1µF
8
7
6
5
JP1
LT1763
IN
GND
GND
SHDN
OUT
ADJ
GND
BYP
1
2
3
4
R7
249k
2
4
6
8
JP2
10
12
14
16
1
3
5
7
9
11
13
15
SHDN
E2
DC368 F01
Figure 1. LT1763 500mA Low Noise Micropower LDO Regulator
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DEMO MANUAL DC368A
pArts List
ITEM
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
QUANTITY
0
1
1
1
4
1
1
1
1
1
1
1
1
1
1
1
1
REFERENCE
ADJ1
C1
C2
C3
E1 to E4
JP1
JP2
SHUNTS FOR JP1
SHUNTS FOR JP2
R1
R2
R3
R4
R5
R6
R7
U1
PART DESCRIPTION
OPT, 0402
CAP X5R 1µF 25V 10%, 0603
.,
CAP X7R 0.01µF 16V 5%, 0402
.,
CAP CER X7R 10µF 10V, 1210
TP TERMINAL TURRET, 1 PIN, 0.064 HOLE
,
JMP 2 PINS 1 ROW .079CC
,
CONN, SMT2X8, 0.39” GAP
SHUNTS, .079” CENTER
SHUNTS 0.39CC
RES., CHIP 56.2k 1/16W 1% 0402
RES., CHIP 118k 1/16W 1% 0402
RES., CHIP 261k 1/16W 1% 0402
RES., CHIP 365k 1/16W 1% 0402
RES., CHIP 422k 1/16W 1% 0402
RES., CHIP 768k 1/16W 1% 0402
RES., CHIP 249k 1/16W 1% 0402
IC, LT1763CS8, SO8
AVX 06033D105KAT2A
AVX 0402YC103JAT1A
TAIYO YUDEN LMK325BJ106MN
Mill-Max 2308-2
COMM-CON 2802S-02-G1
COMM-CON 6351-16P1
COMM-CON CCIJ2MM-138G
COMM-CON CTAIJ1MM-G
AAC CR05-5622FM
AAC CR05-1183FM
AAC CR05-2613FM
AAC CR05-3653FM
AAC CR05-4223FM
AAC CR05-7683FM
AAC CR05-2493FM
LINEAR TECH. LT1763CS8
MANUFACTURE/PART #
dc368afb
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DEMO MANUAL DC368A
operAtion
HOOk-UP
Solid turret terminals are provided for easy connection to
supplies and test equipment. Connect a 0V to 20V, 0.6A
power supply across the IN and GND terminals and the
load across the OUT and GND terminals. The
SHDN
pin
can be disconnected from IN via JP1 to allow for separate
shutdown control via a secondary control line. JP2 can be
used to select any of a number of common fixed output
voltages, or used in conjunction with ADJ1 to create a
custom output voltage using the formula:
ADJ1 = (V
OUT
– 1.22V)/4.93µA
Thermal Characteristics
Demonstration Circuit DC368A has been laid out to illus-
trate and achieve maximum power handling capabilities.
Although a simple two-layer board might have been suf-
ficient for electrical operation of the LT1763, the four-layer
board with vias to internal ground planes offers excellent
thermal characteristics. A two-layer board of the same
size with no thermal vias will exhibit a thermal resistance
of 60°C/W, whereas DC368A exhibits a thermal resistance
of 50°C/W.
OUTPUT CAPACITOR SELECTION
The output capacitor C3 is a 10µF X7R ceramic chip
capacitor. Should a different output capacitor be desired,
care must be exercised with the selection. Many ceramic
capacitor dielectrics exhibit strong temperature and
voltage characteristics that reduce their effective capaci-
tance to as low as 10% to 20% of nominal over the full
temperature range. For further information, see Linear
Technology Application Note 83, “Performance Verifica-
tion of Low Noise, Low Dropout Regulators,” Appendix B,
“Capacitor Selection Considerations,” reprinted below.
CAPACITOR SELECTION CONSIDERATIONS
Bypass Capacitance and Low Noise Performance
Adding a capacitor between the regulator’s V
OUT
and BYP
pins lowers output noise. A good quality, low leakage
capacitor is recommended. This capacitor bypasses the
regulator’s reference, providing a low frequency noise
pole. A 0.01µF capacitor lowers the output voltage noise
to 20µV
RMS
. Using a bypass capacitor also improves
transient response. With no bypassing and a 10µF output
capacitor, a 10mA to 500mA load step settles to within
1% of final value in under 100µs. With a 0.01µF bypass
capacitor, the output settles to within 1% for the same
load step in under 10µs; total output deviation is inside
2.5%. Regulator start-up time is inversely proportional to
bypass capacitor size, slowing to 15ms with a 0.01µF
bypass capacitor and 10µF at the output.
Output Capacitance and Transient Response
The regulators are designed to be stable with a wide range
of output capacitors. Output capacitor ESR affects stabil-
ity, most notably with small capacitors. A 3.3µF minimum
output value with ESR of 3Ω or less is recommended to
prevent oscillation. Transient response is a function of
output capacitance. Larger values of output capacitance
decrease peak deviations, providing improved transient
response for large load current changes. Bypass capaci-
tors, used to decouple individual components powered by
the regulator, increase the effective output capacitor value.
Larger values of reference bypass capacitance dictate
larger output capacitors. For 100pF of bypass capacitance,
4.7µF of output capacitor is recommended. With 1000pF
or more of bypass capacitance, a 6.8µF output capacitor
is required.
The shaded region of Figure B1 defines the regulator’s
stability range. The minimum ESR needed is set by the
amount of bypass capacitance used, while maximum
ESR is 3Ω.
Ceramic Capacitors
Ceramic capacitors require extra consideration. They
are manufactured with a variety of dielectrics, each
with different behavior across temperature and applied
voltage. The most common dielectrics are Z5U, Y5V,
X5R and X7R. The Z5U and Y5V dielectrics provide high
capacitance in a small package, but exhibit strong voltage
and temperature coefficients, as shown in Figures B2
and B3. Used with a 5V regulator, a 10µF Y5V capacitor
shows values as low as 1µF to 2µF over the operating
temperature range. The X5R and X7R dielectrics have
dc368afb
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DEMO MANUAL DC368A
operAtion
more stable characteristics and are more suitable for
output capacitor use. The X7R type has better stability
over temperature, while the X5R is less expensive and
available in higher values.
Voltage and temperature coefficients are not the only prob-
lem sources. Some ceramic capacitors have a piezoelectric
response. A piezoelectric device generates voltage across
its terminals due to mechanical stress, similar to the way
4.0
3.5
STABLE REGION
CHANGE IN VALUE (%)
3.0
2.5
ESR ( )
2.0
1.5
1.0
0.5
0
1
C
BYP
= 0
C
BYP
= 100pF
a piezoelectric accelerometer or microphone works. For a
ceramic capacitor, the stress can be induced by vibrations
in the system or thermal transients. The resulting voltages
can cause appreciable amounts of noise, especially when
a ceramic capacitor is used for noise bypassing. A ceramic
capacitor produced Figure B4’s trace in response to light
tapping from a pencil. Similar vibration-induced behavior
can masquerade as increased output voltage noise.
20
0
–20
–40
–60
–80
–100
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
X5R
C
BYP
= 330pF
C
BYP
≥1000pF
Y5V
3
2
4 5 6 7 8 9 10
OUTPUT CAPACITANCE (µF)
DC368 B1
0
2
4
8
6
10 12
DC BIAS VOLTAGE (V)
14
16
DC368 B2
Figure B1. LT1763 Regulator Stability for Various
Output and Bypass (C
BYP
) Capacitor Characteristics
40
20
CHANGE IN VALUE (%)
0
–20
–40
–60
–80
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
0
50
25
75
TEMPERATURE (C)
100
125
Y5V
X5R
Figure B2. Ceramic Capacitor DC Bias Characteristics
Indicate Pronounced Voltage Dependence. Device Must
Provide Desired Capacitance Value at Operating Voltage
20µV/DIV
–100
–50 –25
DC368 B2
20µV/DIV
DC368 B4
Figure B3. Ceramic Capacitor Temperture Characteristics
Show Large Capacitance Shift. Effect Should Be
Considered When Determining Circuit Error Budget
Figure B4. A Ceramic Capacitor Responds to Light Pencil
Tapping. Piezoelectric Based Response Approaches 80µV
P-P
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