DC368A - Demo Manual

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 package. 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 costsensitive 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
TA = 25°C, VIN = 2.3V, VSHDN = 5V, ILOAD = 1mA, VOUT = 1.22V (JP2 set on Pins 1-2), unless otherwise specified.
PARAMETER
CONDITIONS
MIN
Input Voltage Range
TYP
2.3
MAX
UNITS
20
V
Output Voltage (Note 1)
1.208
1.220
1.232
V
Output Voltage (Note 1)
VIN = 1.5V, JP2 on Pins 5-6
1.478
1.497
1.519
V
Output Voltage (Note 1)
VIN = 1.8V, JP2 on Pins 7-8
1.775
1.802
1.834
V
Output Voltage (Note 1)
VIN = 2.5V, JP2 on Pins 9-10
2.462
2.506
2.563
V
Output Voltage (Note 1)
VIN = 3V, JP2 on Pins 11-12
2.961
3.019
3.093
V
Output Voltage (Note 1)
VIN = 3.3V, JP2 on Pins 13-14
3.235
3.300
3.384
V
Output Voltage (Note 1)
VIN = 5V, JP2 on Pins 15-16
4.897
5.006
5.148
V
Line Regulation
∆VIN = 2.3V to 20V
1
5
mV
Quiescent Current
∆ILOAD = 0mA
30
50
µA
Load Regulation
∆ILOAD = 1mA to 500mA
0.2
1
%
SHDN Pin Threshold
On-to-Off
1.8
V
Output Voltage Noise
0.45
0.65
Off-to-On, ILOAD = 1mA
0.8
ILOAD = 500mA, BW = 10Hz to 100kHz
20
V
µVRMS
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
LT1763 (5V Output)
10Hz to 100kHz Output Noise
DROPOUT VOLTAGE (mV)
450
400
TJ = 125C
350
300
250
VOUT
100µV/DIV
TJ = 25C
200
150
100
50
0
0
50 100 150 200 250 300 350 400 450 500
OUTPUT CURRENT (mA)
COUT = 10µF
IL = 500mA
1ms/DIV
1763 G02
1763 G01
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DEMO MANUAL DC368A
package and schematic diagrams
LT1763CS8
TOP VIEW
OUT 1
8
IN
ADJ 2
7
GND
GND 3
6
GND
BYP 4
5
SHDN
1.22V
C2
0.01µF
S8 PACKAGE
8-LEAD PLASTIC SO
IN
E1
8
JP1
SHDN
C1
1µF
7
6
5
E2
LT1763
IN
OUT
GND
ADJ
GND
GND
SHDN
BYP
C3
10µF
10V
USER
SELECT
1.5V
R1
56.2k
ADJ1
2
1
1.8V
4
2.5V
R2
118k
6
2
8
3V
R3
261k
3.3V
R4
365k
R5
422k
10
12
14
16
9
11
13
15
5V
E3
R6
768k
E4
OUT
GND
JP2
3
1
4
3
5
7
R7
249k
DC368 F01
Figure 1. LT1763 500mA Low Noise Micropower LDO Regulator
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DEMO MANUAL DC368A
PARTS LIST
ITEM
QUANTITY
REFERENCE
PART DESCRIPTION
MANUFACTURE/PART #
1
0
ADJ1
OPT, 0402
2
1
C1
CAP., X5R 1µF 25V 10%, 0603
AVX 06033D105KAT2A
3
1
C2
CAP., X7R 0.01µF 16V 5%, 0402
AVX 0402YC103JAT1A
4
1
C3
CAP CER X7R 10µF 10V, 1210
TAIYO YUDEN LMK325BJ106MN
5
4
E1 to E4
TP, TERMINAL TURRET, 1 PIN, 0.064 HOLE
Mill-Max 2308-2
6
1
JP1
JMP, 2 PINS 1 ROW .079CC
COMM-CON 2802S-02-G1
7
1
JP2
CONN, SMT2X8, 0.39” GAP
COMM-CON 6351-16P1
8
1
SHUNTS FOR JP1
SHUNTS, .079” CENTER
COMM-CON CCIJ2MM-138G
9
1
SHUNTS FOR JP2
SHUNTS 0.39CC
COMM-CON CTAIJ1MM-G
10
1
R1
RES., CHIP 56.2k 1/16W 1% 0402
AAC CR05-5622FM
11
1
R2
RES., CHIP 118k 1/16W 1% 0402
AAC CR05-1183FM
12
1
R3
RES., CHIP 261k 1/16W 1% 0402
AAC CR05-2613FM
13
1
R4
RES., CHIP 365k 1/16W 1% 0402
AAC CR05-3653FM
14
1
R5
RES., CHIP 422k 1/16W 1% 0402
AAC CR05-4223FM
15
1
R6
RES., CHIP 768k 1/16W 1% 0402
AAC CR05-7683FM
16
1
R7
RES., CHIP 249k 1/16W 1% 0402
AAC CR05-2493FM
17
1
U1
IC, LT1763CS8, SO8
LINEAR TECH. LT1763CS8
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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:
pole. A 0.01µF capacitor lowers the output voltage noise
to 20µVRMS. 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.
ADJ1 = (VOUT – 1.22V)/4.93µA
Output Capacitance and Transient Response
Thermal Characteristics
The regulators are designed to be stable with a wide range
of output capacitors. Output capacitor ESR affects stability, 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 capacitors, 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.
Demonstration Circuit DC368A has been laid out to illustrate and achieve maximum power handling capabilities.
Although a simple two-layer board might have been sufficient 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 capacitance to as low as 10% to 20% of nominal over the full
temperature range. For further information, see Linear
Technology Application Note 83, “Performance Verification 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 VOUT 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
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
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4
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 problem sources. Some ceramic capacitors have a piezoelectric
response. A piezoelectric device generates voltage across
its terminals due to mechanical stress, similar to the way
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.
4.0
20
3.5
STABLE REGION
2.5
ESR (Ω)
CHANGE IN VALUE (%)
0
3.0
2.0
CBYP = 0
CBYP = 100pF
1.5
1.0
0.5
0
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
CBYP = 330pF
CBYP≥1000pF
–40
–60
Y5V
–80
–100
3
2
4 5 6 7 8 9 10
OUTPUT CAPACITANCE (µF)
1
X5R
–20
0
2
4
8
6
10 12
DC BIAS VOLTAGE (V)
DC368 B1
Figure B1. LT1763 Regulator Stability for Various
Output and Bypass (CBYP) Capacitor Characteristics
14
16
DC368 B2
Figure B2. Ceramic Capacitor DC Bias Characteristics
Indicate Pronounced Voltage Dependence. Device Must
Provide Desired Capacitance Value at Operating Voltage
40
CHANGE IN VALUE (%)
20
X5R
0
–20
–40
Y5V
–60
–80
20µV/DIV
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
–100
–50 –25
0
50
25
75
TEMPERATURE (C)
100
125
DC368 B2
Figure B3. Ceramic Capacitor Temperture Characteristics
Show Large Capacitance Shift. Effect Should Be
Considered When Determining Circuit Error Budget
20µV/DIV
DC368 B4
Figure B4. A Ceramic Capacitor Responds to Light Pencil
Tapping. Piezoelectric Based Response Approaches 80µVP-P
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DEMO MANUAL DC368A
operation
Output Voltage Noise
Measuring output voltage noise can be a tricky process,
further complicated by the low levels of noise inherent
in a circuit such as this. Consideration must be given
to regulator operating conditions, as well as the noise
bandwidth of interest. Linear Technology has invested an
enormous amount of time to provide accurate, relevant
data to customers regarding noise performance. For further
information on measuring output voltage noise, see Linear
Technology Application Note 83, “Performance Verification
of Low Noise, Low Dropout Regulators.”
Noise Testing Considerations
What noise bandwidth is of interest and why is it interesting? In most systems, the range of 10Hz to 100kHz is the
information signal processing area of concern. Additionally,
linear regulators produce little noise energy outside this
region.1 These considerations suggest a measurement
bandpass of 10Hz to 100kHz, with steep slopes at the
band limits. Figure 2 shows a conceptual filter for LDO
noise testing. The Butterworth sections are the key to
IN
5Hz SINGLE ORDER
HIGHPASS
GAIN = 60dB
10Hz 2nd ORDER
BUTTERWORTH HP
steep slopes and flatness in the passband. The small input
level requires 60dB of low noise gain to provide adequate
signal for the Butterworth filters. Figure 3 details the filter
scheme. The regulator under test is at the diagram’s center.2
A1–A3 make up a 60dB gain highpass section. A1 and
A2, extremely low noise devices (<1nV√Hz), comprise a
60dB gain stage with a 5Hz highpass input. A3 provides a
10Hz, 2nd order Butterworth highpass characteristic. The
LTC®1562 filter block is arranged as a 4th order Butterworth lowpass. Its output is delivered via the 330µF‑100Ω
highpass network. The circuit’s output drives a thermally
responding RMS voltmeter.3 Note that all circuit power
is furnished by batteries, precluding ground loops from
corrupting the measurement.
Note 1: Switching regulators are an entirely different proposition,
requiring very broadband noise measurement.
Note 2: Component choice for the regulator, more critical than might
be supposed, is discussed in “Capacitor Selection Considerations.”
Note 3: The choice of the RMS voltmeter is absolutely crucial to
obtaining meaningful measurements. See Appendix C, Application
Note 83 “Understanding and Selecting RMS Voltmeters.”
100kHz 4th ORDER
BUTTERWORTH LP
5Hz SINGLE ORDER
HIGHPASS
10Hz TO 100kHz
DC368 F02
Figure 2. Filter Structure for Noise Testing LDOs. Butterworth
Sections Provide Appropriate Response in Desired Frequency Range
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DEMO MANUAL DC368A
operation
EXTERNAL INPUT
+
+
330µF
+
INPUT
100Ω
100Ω
A1
LT1028
6.19k
3.16k
1µF
4.99k
A3
LT1224
–
2k
2.49k
5.9K
VIN
IN
+
NORMAL
INPUT
–
–
4.5V
4.7µF 4.7µF
A2
LT1028
–4.5V
5VOUT
OUT
LT1763-5
0.01µF
SHDN
BYP
GND
+
10µF
RLOAD
(TYPICALLY
150mA)
TYPICAL REGULATOR UNDER TEST
10k
10k
1
20
5.62k
2
19
13k
10k
3
18
10k
4
17
5
16
6
15
7
14
110k
8
13
110k
17.8k
9
12
43.2k
10
11
–4.5V
4.5V
110k
LTC1562
–4.5V
OUTPUT TO THERMALLY RESPONDING
RMS VOLTMETER
0.1V FULL SCALE = 100µVRMS NOISE
10Hz TO 100kHz BW
330µF
100Ω
+
ALL RESISTORS 1% METAL FILM
4.7µF CAPACITORS = MYLAR, WIMA MKS-2
330µF CAPACITORS = SANYO OSCON
±4.5V DERIVED FROM 6AA CELLS
POWER REGULATOR FROM APPROPRIATE
NUMBER OF D SIZE BATTERIES
110k
DC368 F03
Figure 3. Implementation of Figure 2. Low Noise Amplifiers Provide Gain and Initial
Highpass Shaping. LTC1562 Filter Supplies 4th Order Butterworth Lowpass Characteristic
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DEMO MANUAL DC368A
pcb layout and film
Silkscreen Top
Paste Mask Top
Solder Mask Top
Layer 1, Component Side*
Layer 4, Solder Side*
Layer 3, GND Plane*
Layer 2, GND Plane*
Solder Mask Bottom
* These layers are shorted to L1 with Vias and function as heat dispersants.
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DEMO MANUAL DC368A
pc fab drawing
2.000
D
A
C
2.000
C
A
C
D
B
C
NOTES: UNLESS OTHERWISE SPECIFIED
1. MATERIAL: FR4 OR EQUIVALENT EPOXY, 2 OZ. COPPER CLAD
THICKNESS 0.062 0.006 TOTAL OF 4 LAYERS.
2. FINISH: ALL PLATED HOLES 0.001 MIN./0.005 MAX. COPPER PLATE
ELECTRODEPOSITED TIN-LEAD COMPOSITION BEFORE REFLOW.
SOLDER MASK OVER BARE COPPER (SMOBC).
3. SOLDER MASK: BOTH SIDES USING LPI OR EQUIVALENT.
4. SILKSCREEN: USING WHITE EPOXY NON-CONDUCTIVE INK.
5. UNUSED SMD COMPONENTS SHOULD BE FREE OF SOLDER.
6. FILL UP ALL VIAS WITH SOLDER.
7. SCORING:
0.020
NUMBER
SYMBOL DIAMETER OF HOLES
A
0.02
25
B
0.035
2
C
0.064
4
D
0.07
2
TOTAL HOLES
33
PLATED
YES
YES
YES
NO
0.017
dc368afb
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation
that the interconnection of its circuits as described herein will not infringe on existing patent rights.
9
DEMO MANUAL DC368A
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions:
This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT
OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete
in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety
measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.
If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date
of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU
OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS
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ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
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arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all
appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or
agency certified (FCC, UL, CE, etc.).
No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance,
customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.
LTC currently services a variety of customers for products around the world, and therefore this transaction is not exclusive.
Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and
observe good laboratory practice standards. Common sense is encouraged.
This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC application engineer.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation
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10 Linear Technology Corporation
LT 0713 REV B • PRINTED IN USA
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