Linear Technology DC193 Quick setup guide

1
DEMO MANUAL DC193
NO DESIGN SWITCHER
OUTPUT CURRENT (A)
0.01
100
95
90
85
80
75
70 0.10 1.00
DC193 • TPC01
EFFICIENCY (%)
V
IN
= 3.3V
V
OUT
= 2.5V
PARAMETER CONDITION VALUE
Input Voltage Range Operating Input Voltage 2.5V to 6V
Maximum Input Voltage 7V
Output Voltage Set by Jumper, J1, in J1A Position 2.5V ±0.06V
Set by Jumper, J1, in J1B Position 3.3V ±0.10V
Set by Jumper, J1, in J1C Position and add Optional Adjust Resistor, R6 2.5V to 5V
Typical Supply Current I
OUT
= 0mA, V
IN
= 3.5V 165µA
LTC1626 Single-Cell Li-Ion,
High Efficiency, Step-Down
DC/DC Converter
DESCRIPTIO
U
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
PERFORMANCE SUMMARY
UWWW
The DC193 demonstration circuit is a step-down (buck)
regulatorusingtheLTC
®
1626operatingfromasingle-cell
Li-Ionbatterypack.Theoutputvoltageiseasilysetto2.5V
or 3.3V with a simple jumper selection. Other output
voltages can be programmed with an optional resistor.
ThedemoboardhighlightsthecapabilitiesoftheLTC1626,
which is able to smoothly shift from a high efficiency
switch-mode DC/DC regulator to a low-dropout linear
regulator (i.e., 100% duty cycle) when the Li-Ion battery
voltagedropstoneartheoutputvoltage.Whenthebattery
voltage rises again, the LTC1626 smoothly shifts back to
a high efficiency DC/DC converter. At low load currents,
the LTC1626 automatically switches to Burst Mode
TM
operation to reduce switching losses and maintain high
operatingefficiencies.Further,theLTC1626drawsamere
0.5µAwheninshutdownmode.Abuilt-in0.32ΩP-channel
switchallowsupto0.6Aofoutputcurrentandprovidesup
to 95% efficiency. Exclusive use of small surface mount
components results in a highly efficient application in a
very small board space.
Gerberfilesforthiscircuitboardareavailable.Callthe
LTC factory.
Efficiency vs Load Current
TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO
UUW
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2
DEMO MANUAL DC193
NO DESIGN SWITCHER
PACKAGE AND SCHEMATIC DIAGRAMS
WWU
Figure 1. DC193 Schematic Diagram
113
LB
OUT
SHDN
I
TH
PWR V
IN
PWR V
IN
C
T
PGND
SENSE
+
SENSE
–
V
FB
SGND
LTC1626
3
10
6
5
12
LB
IN
4
V
IN
V
OUT
SW
214
8
7
9
11
R1
22K
R2
1K
D1
MBR0520LT1
(J1A = 2.5V)
(J1B = 3.3V)
(J1C = ADJ)
*MOVE JUMPER TO J1C AND
ADD RESISTOR, R6, FOR V
OUT
ADJUST
R6 = 10k/[(V
OUT
/1.25) – 1]
R
SENSE

0.1Ω
L1
22µH
DC193 • SCHEMATIC
TOP VIEW
S14 PACKAGE
14-LEAD PLASTIC SOIC
1
2
3
4
5
6
7

14
13
12
11
10
9
8

PWR V
IN

V
IN

LB
OUT

LB
IN

C
T

I
TH

SENSE
–



SW
PWR V
IN

PGND
SGND
SHDN
V
FB
SENSE
+


C3
0.1µF
16V
+
C
IN
47µF
10V
V
IN
LB
IN
LB
OUT
SHDN
C1
3900pF C2 270pF
R4
10k
1%
J1A
R5
6.04k
1%
J1B
R6*
J1C
C5
100pF
C4
1000pF
+
C
OUT
100µF
6.3V
R3
10k
1%
LTC1626
PERFORMANCE SUMMARY
UWWW
PARAMETER CONDITION VALUE
Maximum Output Current 0.6A
Typical Switch ON Resistance T
J
= 25°C, V
IN
= 4.5V 0.32
T
J
= 25°C, V
IN
= 3.5V 0.40
T
J
= 25°C, V
IN
= 2.5V 0.50
SHDN Pin Thresholds Minimum Voltage for the LTC1626 to be Shutdown V
IN
–0.4V
Minimum Voltage for the LTC1626 to be Active 0.4V
Low Battery Threshold Voltage at LBI Input Pin 1.25 ±0.1V
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3
DEMO MANUAL DC193
NO DESIGN SWITCHER
PARTS LIST
QUICK START GUIDE
The DC193 demonstration board is easy to set up to
evaluatetheperformance oftheLTC1626. Pleasefollow
the procedure outlined below for proper operation.
• Select the output voltage by moving jumper J1 to
either the J1A (2.5V) or J1B (3.3V) position. If a
differentoutputvoltageisdesired,moveJ1totheJ1C
position and add optional V
OUT
adjust resistor, R6.
V
OUT
should not be programmed above 5V unless
C
OUT
ischangedfrom a6.3Vtoa10Vrating .Thevalue
of R6 is calculated as follows:
R6 = 10k/[(V
OUT
/1.25) –1)]
• Connect the input power supply to the V
IN
and GND
terminals. V
IN
should be limited to 6V.
• TheLB
OUT
pinisacurrentsinkingpin.WhentheLB
IN
pindropsbelow1.25V,the LB
OUT
pinwillsink400µA
of current.
• The LB
IN
pin is the low-battery detector input pin.
Normally, its input comes from the input voltage,
through a resistive divider network (see Figure 3).
• Connect the load between the V
OUT
and GND termi-
nals. The load current should not exceed 600mA.
• RefertoFigure4forproperarrangementofmeasure-
ment equipment setup.
• TheSHDNpinispulleddowntogroundbyR1.Toput
the LTC1626 in shutdown, connect the SHDN
pin directly to V
IN
. (The shutdown current will be
dominated by the current flowing through pull-down
resistor, R1; that is, the current measured at V
IN
will
be V
IN
/22k. To measure the shutdown current of the
LTC1626, remove R1 and switch the SHDN pin to
either GND or V
IN
.)
REFERENCE
DESIGNATOR QUANTITY PART NUMBER DESCRIPTION VENDOR TELEPHONE
C1 1 AVX 06035C392KAT 3900pF 50V X7R Chip Capacitor AVX [phone]
C2 1 AVX 06035A271KAT 270pF 50V NPO Chip Capacitor AVX [phone]
C3 1 AVX 0603YC104KAT 0.1µF 16V X7R Chip Capacitor AVX [phone]
C4 1 AVX 0603C102KAT 1000pF 50V X7R Chip Capacitor AVX [phone]
C5 1 AVX 0603A101KAT 100pF 50V NPO Chip Capacitor AVX [phone]
C
IN
1 TPSC476M010R0350 47µF 10V Tantalum Capacitor AVX [phone]
C
OUT
1 TPSC107M006R0150 100µF 6.3V Tantalum Capacitor AVX [phone]
D1 1 MBR0520LT1 0.5A 20V Schottky Rectifier Diode Motorola [phone]
R1 1 TAD CR16-223JM 22k 1/16W 5% Chip Resistor TAD [phone]
R2 1 TAD CR16-102JM 1k 1/16W 5% Chip Resistor TAD [phone]
R3, R4 2 TAD CR16-1002JM 10k 1/16W 1% Chip Resistor TAD [phone]
R5 1 TAD CR16-6041JM 6.04k 1/16W 1% Chip Resistor TAD [phone]
R
SENSE
1 LR120601R100J 0.1W 1/4W 5% Chip Resistor IRC [phone]
L1 1 CD54-220 22µH Inductor Sumida [phone]
U1 1 LTC1626CS IC LTC [phone]
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4
DEMO MANUAL DC193
NO DESIGN SWITCHER
OPERATIO
U
ThecircuitshowninFigure2operatesfrominputvoltages
from2.5Vto6V.Theoutputvoltageiseither2.5V,3.3Vor
adjustable between 2.5V and 5V, depending upon the
position of jumper J1.
This demonstration unit is intended for the evaluation of
theLTC1626switchingregulatorICandwasnotdesigned
for any other purpose.
LTC1626 OPERATION
When the load is heavy, the LTC1626 is in continuous
mode, which operates as follows: the internal P-channel
MOSFETswitchisturnedonattheendoftheoff-timeand
turned off when the inductor current has risen to the
current comparator threshold. During the off-time, the
catch diode D1 turns on. At the end of the off-time, the
P-channel MOSFET is again turned on, and the cycle
repeats.
However, when the load is relatively light, the LTC1626
automatically switches to Burst Mode operation. In this
mode, the output voltage is regulated by a hysteretic
comparator that, when tripped, shuts down the MOSFET
driveandcontrolcircuitrytoconserveDCsupplycurrent.
From the time the comparator trips until the lower com-
parator threshold is reached, the load current is supplied
by the charge stored in the output capacitor. When the
output capacitor discharges to the lower threshold, the
main loop again briefly turns on at a low current level to
rechargethecapacitor.Thiscyclerepeatsatprogressively
slower rates as the output current is reduced.
Astheinputsupplyvoltagedropsneartheoutputvoltage,
theLTC1626shiftssmoothlyfromahighefficiencyswitch-
mode DC/DC regulator to a low dropout linear regulator
(i.e., 100% duty cycle). When the battery voltage rises
again, the LTC1626 smoothly shifts back to a high effi-
ciency DC/DC converter.
Figure 2. LTC1626 Block Diagram
PGND SW
DC193 • BD
14
SGND
11
LB
OUT
3
PWR V
IN
1, 13
12
C
T
5
V
IN
2
SENSE
+
8SENSE
–
7
R
Q
S
–
+
–
+
V
TH1
SLEEP
–
+
V
TH2
C
–
+
–
+
G
S
–
+
T
OFF-TIME
CONTROL SENSE
–
V
FB
SHDN
25mV to 150mV
10
I
TH
V
OS
13k
6
REFERENCE
LB
IN
4
V
FB
9
+–
V
A3
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5
DEMO MANUAL DC193
NO DESIGN SWITCHER
OPERATIO
U
LOW-BATTERY DETECTION
Thelow-batterydetectorsensestheinputvoltagethrough
anexternalresistordivider.Thisdividedvoltageconnects
to the (–) input of a voltage comparator (LB
IN
) and is
comparedtoaninternal1.25Vreferencevoltage.Neglect-
ing LB
IN
input bias current, the following expression is
used for setting the trip voltage threshold:
1 + R
LB2

R
LB1
V
LB_TRIP
= 1.25
) )
TheLB
OUT
isanN-channelopen-drainthatgoeslowwhen
the battery voltage drops below the threshold voltage. In
shutdown,thecomparatorisdisabled andLB
OUT
isinthe
high impedance state. Figure 3 is a schematic diagram
detailing the low-battery comparator connection and
operation.
–
+
C
FILTER

0.01µFR
LB1

1%
1.25V
LTC1626
LB
IN
V
IN
LB
OUT
R
LB2

1%
DC193 • F03
Figure 3. Low-Battery Comparator
HOW TO MEASURE VOLTAGE REGULATION
When measuring voltage regulation, remember that all
measurements must be taken at the point of regulation,
that is, where the LTC1626's control loop looks for the
information to keep the output voltage constant. This
information occurs between Pin 7 and Pin 11 of the
LTC1626. These points correspond to the output termi-
nals of the demonstration board. Test leads should be
attachedtotheseterminals. Measurementsshouldnotbe
takenat the endof test leadsatthe load. Refer toFigure 4
for proper monitoring equipment configuration.
+
A
+
V
+
V
OUT
GND
+
V
LOAD
LB
OUT
LB
IN
SHDN
GND
V
IN
LTC1626
SINGLE CELL
LI-ION, STEP-DOWN
CONVERTER
DC193
+
A
DC193 • F04
Figure 4. Proper Measurement Setup
Whenperforminglineorloadregulationtests,alwayslook
at the input voltage across the input terminals. For the
purposesofthesetests,thedemonstration circuitshould
be fed from a regulated DC bench supply, so additional
variations on the DC input do not add errors to the
regulation measurements.
RIPPLE MEASUREMENT
To measure output ripple voltage, it is best to measure
directly across the output terminals.
As in the previous regulation tests, the supply must be a
regulated DC source so that the ripple on the input to the
circuitundertestdoesnotaddtotheoutputripple,causing
errors in the measurement.
The technique used to measure the output ripple is also
important. Here is a list of things to do and not do when
using a scope probe:
1. DO NOT USE THE GROUND LEADS/CLIPS THAT ARE
ATTACHED TO THE SCOPE PROBE!
2. DOATTACHTHESHIELDOFTHEPROBEBODYTOTHE
NEGATIVESIDEOFTHEOUTPUTCAPACITOR!DONOT
USE WIRE!
3. DO PUT THE TIP OF THE SCOPE PROBE DIRECTLY
ON THE POSITIVE TERMINAL OF THE OUTPUT
CAPACITOR
4. DO NOT USE A PROBE WHOSE BODY IS NOT COM-
PLETELY SHIELDED.
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6
DEMO MANUAL DC193
NO DESIGN SWITCHER
OPERATIO
U
Any unshielded lead, such as a ground lead on a scope
probe, acts as an antenna for the switching noise in the
supply. Therefore, any use of ground lead will invalidate
the measurement.
Further,beextremelycarefultoensurethatothersources
of noise do not invalidate the measurement. Noise from
the60Hzpowerlinethatfeedsthebenchsupplypowering
theLTC1626demonstrationboardcancauseerrorsinthe
measurement. This noise (especially spikes) can propa-
gate through the supply and appear on the ground of the
demonstration unit. If this is a problem, a battery can be
used to power the unit for ripple tests.
Also,bewaryofgroundloops.TheDCsupplyshouldfloat,
and the only ground should be that of the scope probe.
Never float the oscilloscope, as it may present a safety
hazard.
An alternative technique is to take a 50Ωor 75Ωpiece of
coaxandsolder theleads directlyto theoutputcapacitor.
Keep the shield over the center conductor for as great a
distance as possible. The center conductor can pick up
strayradiation whennot shielded, sominimize thelength
of exposed center conductor. The other end of the coax
should have a BNC connector for attaching to the
oscilloscope.
CHECKING TRANSIENT RESPONSE
Switching regulators take several cycles to respond to a
DC(resistive)loadcurrent.Whenaloadstepoccurs,V
OUT
shifts by an amount equal to ∆I
LOAD
• ESR, where ESR is
theeffectiveseriesresistanceofC
OUT
.∆I
LOAD
alsobegins
tochargeordischargeC
OUT
untiltheregulatorloopadapts
tothecurrentchangeandreturnsV
OUT
toitssteady-state
value. During this recovery time, V
OUT
can be monitored
for overshoot or ringing, which would indicate a stability
problem.TheexternalcomponentsshowninFigure1will
prove adequate for most applications.
Asecond,moresevere,transientiscausedbyswitchingin
loads with large (>1µF) supply bypass capacitors. The
dischargedbypasscapacitorsareeffectivelyputinparallel
withC
OUT
,causingarapid dropinV
OUT
.Noregulatorcan
deliverenough current to prevent this problemif the load
switch resistance is low and it is driven quickly. The only
solutionis tolimit therise timeof the switchdrive sothat
the load rise time is limited to approximately 25 • C
LOAD
.
Thus, a 10µF capacitor would require a 250µs rise time
limiting the charging current to about 200mA.
COMPONENTS
Component selection can be very critical in switching
power supply applications. The LTC1626 data sheet de-
tailsmore specificselection criteria formost ofthe exter-
nalcomponentssurroundingtheIC.Besuretorefertothe
data sheet if changes to this demonstration board are
anticipated.
Capacitors
InthecircuitshowninFigure1,C
IN
andC
OUT
arelowESR,
high ripple-current tantalum capacitors specifically de-
signedfor use inswitching powersupplies. ESR (equiva-
lent series resistance) is the parasitic series resistance in
the capacitor. Very often this resistance is the limiting
factor in reducing ripple at the output or input of the
supply. Standard electrolytic capacitors may cause the
feedback loop to be unstable (that is, your power supply
may become an oscillator). Also, they may cause poor
transientresponseorhavelimitedoperatinglife.Standard
capacitors generally do not have an ESR specification at
highfrequencies,forexampleat100kHz.So,althoughyou
may find a capacitor that works to your satisfaction in a
prototype, the same part may not work consistently in
production .
Standardtantalumcapacitors(mostnotably,thelowcost
ones) are not recommended for use in LTC1626 applica-
tions as they do not have the ability to take the large peak
currents that are required for the application. Tantalum
capacitors have a failure mechanism whereby they be-
come a low value resistor or short.
One alternative to tantalum and electrolytic capacitors is
organicsemiconductortypecapacitors(OSCONs)thatare
specifically made for power supply applications. They
exhibit very low ESR and are roughly one-half the size of
an equivalent electrolytic capacitor.
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7
DEMO MANUAL DC193
NO DESIGN SWITCHER
OPERATIO
U
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 represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
Inductor
The inductor size, shape, efficiency, form factor and cost
are variables that can be traded off against one another.
The only fixed requirement of the inductor used with the
LTC1626 is that it must be able to support the output DC
current and still maintain its inductance value.
Although the inductor used in the demo board is from
Sumida, there are a wide variety of inductors available
fromother manufacturers.Coilcraft's DO3316 seriesand
CoiltronicsCTXseriesarealsosuitableinthisdemoboard.
However, recharacterizing the circuit for efficiency is
necessaryifanyofthealternateinductorsareusedinplace
of the existing one.
Wesuggestyoucontactsomeoftheinductormanufactur-
ers in Table 1 and discuss your needs with them. Very
often, a standard low cost solution which will meet your
needs is on the shelf.
Sense Resistor
Thecurrentsenseresistorspecifiedinthecomponentlist
is manufactured by IRC. Alternative resistor sources in-
clude Dale and KRL/Bantry.
Schottky Diode
At high input voltages, the diode conducts most of the
time. As V
IN
approaches V
OUT
, the diode conducts only a
smallfractionofthetime.Themoststressfulconditionfor
thediodeis whentheoutputis shortcircuited.Under this
condition the diode must safely handle I
PEAK
at close to
100% duty cycle. Schottky diodes are a good choice for
lowforwarddropandfastswitchingtimes.MostLTC1626
circuitswillbewellservedbyanMBRS0520LT1Schottky
diode.
Component Manufacturers
Besides those components that are used on the demon-
strationboardothercomponentsmayalsobeused.Below
is a partial list of the manufacturers whose components
you can use for the switching regulator. Using compo-
nents other than the ones on the demonstration board
requires recharacterizing the circuit for efficiency.
Table 1. Inductor Manufacturer
MANUFACTURER PART NUMBERS
Coilcraft D03316 Series
1102 Silver Lake Road
Cary, IL 60013
(Phone) 847-639-6400
(Fax) 847-639-1469
Coiltronics International Econo-Pac
6000 Park of Commerce Blvd. Octa-Pac
Boca Raton, FL 33487
(Phone) 561-241-7876
(Fax) 561-241-9339
Dale Electronics Inc. LPT4545
E. Highway 50
P.O. Box 180
Yankton, SD 57078-0180
(Phone) 605-665-9301
(Fax) 605-665-1627
Sumida Electric Co. Ltd. CD 74B Series
5999 New Wilke Rd., Suite #110 CD 75 Series
Rolling Meadows, IL 60008 CDR105B
(Phone) 847-956-0666
(Fax) 847-956-0702
Table 2. Capacitor Manufacturers
MANUFACTURER PART NUMBERS
AVX Corporation TPS Series
P.O. Box 867
Myrtle Beach, SC 29578
(Phone) 803-946-0349
(Fax) 803-448-2170
Sanyo Video Components OS-CON Series
2001 Sanyo Avenue
San Diego, CA 92173
(Phone) 619-661-6835
(Fax) 619-661-1055
Sprague 593D Series
678 Main Street
Sanford, ME 04073
(Phone) 207-324-4140
(Fax) 207-324-7223
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8
DEMO MANUAL DC193
NO DESIGN SWITCHER
dc193f LT/TP 0298 500 • PRINTED IN USA
 LINEAR TECHNOLOGY CORPORATION 1998
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
[phone]
FAX: [phone]
●
TELEX: 499-3977
●
www.linear-tech.com
PC FAB DRAWI G
U
PCB LAYOUT A D FIL


UW
Component Side Silkscreen Component Side Component Side Mask
Solder Side Solder Side Mask Pastemask Top
DIAMETER NUMBER OF
SYMBOL (INCH) HOLES PLATED
A 0.020 7 YES
B 0.040 6 YES
C 0.072 2 NO
D 0.094 7 YES
TOTAL HOLES 22
NOTES: UNLESS OTHERWISE SPECIFIED
1. MATERIAL: 2 LAYERS, 0.062" THK. FR-4 GLASS EPOXY 2 OZ. COPPER CLAD.
2. ALL HOLES SHALL BE PLATED THRU.
3. PLATE THRU HOLES WITH COPPER .0014 MIN. THICKNESS. ALL HOLE SIZES IN HOLE
TABLE ARE AFTER PLATING.
4. SILKSCREEN: WITH WHITE EPOXY NON-CONDUCTIVE INK.
5. FINISH: ELECTRODEPOSITED TIN-LEAD COMPOSITION. BEFORE REFLOW. SOLDER
MASK OVER BARE COPPER (SMOBC).
6. SOLDER MASK: USE FILM PROVIDED, BLUE OR GREEN.
7. SCORING:
2.000"
2.000"
B (6 plcs)
C
C
D
D
D
AA
A
A
A
A
A
D
D
D
D
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