DEMO MANUAL DC195
NO-DESIGN SWITCHER
LTC1627 Monolithic
Synchronous Step-Down Regulator
DESCRIPTIO
Demonstration circuit DC195 is a constant-frequency
step-down converter using an LTC
®
1627 monolithic syn-
chronous regulator. It provides low input voltage, high
efficiency conversion for cell phones and other portable
electronics operating from one or two Li-Ion cells or three
to six NiCd cells. Constant 350kHz operation and up to
500mA output capability in an SO-8 package provide a low
noise, space-efficient solution for wireless applications.
The circuit highlights the capability of the the LTC1627.
Designed to work at low voltages, the input voltage (V
IN
)
can range from 2.65V to 8.5V. At input voltages lower than
PERFOR A CE SU
SYMBOL
V
IN
V
OUT
PARAMETER
Input Voltage Range
Output Voltage
I
Q
Forced Continuous Supply Current
V
IN
= 5V, SYNC/FCB = 0V, RUN/SS = 2V, I
OUT
= 0mA
TM
Burst Mode Enabled Supply Current V
IN
= 5V, SYNC/FCB = 2V, RUN/SS = 2V, I
OUT
= 0mA
Shutdown Current
V
IN
= 5V, RUN/SS = 0V, I
OUT
= 0mA
TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTOS
LTC1627 Efficiency Curve
100
JP1 = “≥ 5V”
90
EFFICIENCY (%)
JP1 = “< 5V”
80
EFFICIENCY (%)
90
100
V
IN
= 5V
LTC1627 Efficiency Curve
80
V
IN
= 8.5V
70
V
IN
= 3.6V
V
OUT
= 2.5V
60
1
10
100
LOAD CURRENT (mA)
1000
195 TPC01
70
V
OUT
= 3.3V
JP1 = “≥ 5V”
60
1
10
100
LOAD CURRENT (mA)
1000
195 TPC02
U
WW
U W
U W
U
4.5V, a charge pump bootstrapped to the SW node can be
enabled via a jumper to produce a negative supply. This
supply is used by the top driver to increase the gate
overdrive of the top P-channel MOSFET, lowering its
R
DS(ON)
and increasing efficiency. At V
IN
< 2.5V, the
LTC1627 shuts down and draws just a few microamperes,
making it ideal for single lithium-ion battery applications.
The output voltage is programmable from 1.8V to 3.3V via
a second jumper.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
ARY
CONDITIONS
JUMPER POSITION
JP1 = “≥ 5V”
JP1 = “< 5V”
See Figure 2
JP2 = “1.8V”
JP2 = “2.5V”
JP2 = “2.9V”
JP2 = “3.3V”
JP2 = “OPEN”
JP1 = “≥ 5V,” JP2 = “3.3V”
JP1 = “≥ 5V,” JP2 = “3.3V”
JP1 = “≥ 5V,” JP2 = “3.3V”
VALUE
2.65V to 8.5V
2.65V to 4.5V
1.82V
±
0.043V
2.52V
±
0.06V
2.94V
±
0.07V
3.33V
±
0.079V
Note 1
3.5mA
200µA
15µA
Demo Board
1
DEMO MANUAL DC195
NO-DESIGN SWITCHER
DESCRIPTIO
At low output currents, the LTC1627 automatically switches
to Burst Mode operation to reduce switching losses and
maintain high operating efficiencies. In switching-noise
sensitive applications, Burst Mode operation can be inhib-
PERFOR A CE SU
SYMBOL
I
OUT
f
OSC
V
RIPPLE
V
OUT
V
FCB
V
SYNC
V
RUN/SS
PARAMETER
Minimum Output Current
Operating Frequency
Typical Output Ripple
Typical Load Regulation
Forced Continuous Threshold Voltage
Synchronize Threshold Voltage
Minimum Shutdown Threshold Voltage
Note 1:
Programmable via optional R5. V
OUT
= 0.8V(1 + 210k/R5)
PACKAGE A D SCHE ATIC DIAGRA S
C4
47pF
OPTIONAL
C
C1
1
I
TH
SYNC/FCB
8
E1
SYNC/FCB
R
C
C
SS
, 0.1µF
2
RUN/SS
LTC1627
V
DR
V
IN
SW
7
3
4
V
FB
GND
6
5
L1, 10µH
R6
210k
R7
10Ω
C1
0.1µF
E2
RUN/SS
D1
BAT54S
JP1
V
IN
< 5V
JP1
V
IN
≥
5V
+
C
OUT
100µF
6.3V
* D2 IS FOR PROTECTION AGAINST MISAPPLIED INPUT VOLTAGES WITH JP1 IN THE "< 5V" POSITION.
** SPACE IS PROVIDED FOR AN OPTIONAL RESISTOR TO PROGRAM A CUSTOM OUTPUT VOLTAGE. THE OUTPUT VOLTAGE MUST NOT EXCEED 3.3V.
Figure 1. LTC1627 Constant Frequency, High Efficiency Converter
2
+
C2
0.1µF
W
WW
W
U
U
ited by grounding the SYNC/FCB pin or synchronizing it
with an external clock.
Gerber files for this circuit board
are available. Call the LTC factory.
U W
ARY
CONDITIONS
V
IN
= 5V, V
OUT
= 3.3V
V
IN
= 3V, V
OUT
= 2.5V
Unsynchronized
Synchronized
I
OUT
= 500mA, V
IN
= 5V, V
OUT
= 3.3V
0mA < I
OUT
< 0.5A, V
IN
= 5V, V
OUT
= 3.3V
JUMPER POSITION
JP1= “≥ 5V”
JP1= “< 5V”
All
All
JP1= “≥ 5V”
JP1= “≥ 5V”
All
All
All
VALUE
500mA
500mA
350kHz
385kHz to 525kHz
30mV
P-P
0.5%
0.8V
1.2V
0.4V
TOP VIEW
I
TH
1
RUN/SS 2
8
7
6
5
SYNC/FCB
V
DR
V
IN
SW
LTC1627CS8
V
FB
3
GND 4
S8 PACKAGE
8-LEAD PLASTIC SO
D2*
10V
C3
0.1µF
C
IN
22µF
16V
E6
V
IN
≤
8.5V
E5
V
OUT
E4
V
OSENSE
R4
66.5k
3.3V
R5**
OPTIONAL
OPEN
E3/E7
GND
R1
165k
1.8V
R2
97.6k
2.5V
R3
78.7k
JP2
2.9V
DC195 • SCHEMATIC
DEMO MANUAL DC195
NO-DESIGN SWITCHER
PARTS LIST
REFERENCE
DESIGNATOR
C
IN
C
OUT
C1, C2, C3, C
SS
C4
C
C1
D1
E1 to E6
JP1
JP2
JP1, JP2
L1
D2
R1
R2
R3
R4
R6
R7
R5
R
C
U1
1
LTC1627CS8
1
6
1
1
2
1
1
1
1
1
1
1
1
BAT54S
2501-2
3914-04-G2
3914-10-G2
50633-R
CD54-150MC
MMBZ5240B
CR16-1653FM
CR16-9762FM
CR16-7872FM
CR16-6652FM
CR16-2103FM
CR16-100JM
QUANTITY
1
1
4
1
PART NUMBER
TPSC226M016R0375
TPSC107M006R0150
0603YC104KAT
06035A470JAT
DESCRIPTION
22µF 16V TPS Tantalum Capacitor
100µF 6V TPS Tantalum Capacitor
0.1µF 16V X7R Chip Capacitor
47pF 50V NPO Chip Capacitor
Optional
Dual Schottky Diode in SOT-23
Turret, Testpoint
0.05" Double Row Header
0.05" Double Row Header
0.05" Center Shunt
15µH 20% Inductor
10V Zener Diode in SOT-23
165k 1% 1/16W Chip Resistor
97.6k 1% 1/16W Chip Resistor
78.7k 1% 1/16W Chip Resistor
66.5k 1% 1/16W Chip Resistor
210k 1% 1/16W Chip Resistor
10Ω 5% 1/16W Chip Resistor
Optional
Optional
Monolithic Synchronous Step-Down Regulator
LTC
(408) 432-1900
Zetex
Mill-Max
COMM CON
COMM CON
COMM CON
Sumida
Motorola
TAD
TAD
TAD
TAD
TAD
TAD
(516) 543-7100
(516) 922-6000
(818) 301-4200
(818) 301-4200
(818) 301-4200
(847) 956-0666
(602) 244-3576
(800) 508-1521
(800) 508-1521
(800) 508-1521
(800) 508-1521
(800) 508-1521
(800) 508-1521
VENDOR
AVX
AVX
AVX
AVX
TELEPHONE
(803) 448-9411
(803) 448-9411
(803) 946-0362
(803) 946-0362
3
DEMO MANUAL DC195
NO-DESIGN SWITCHER
QUICK START GUIDE
This demonstration board is easily set up to evaluate the
performance of the LTC1627 IC. Please follow the proce-
dure outlined below for proper operation.
• Refer to Figure 6 for proper connection of monitoring
equipment to ensure correct measurement.
• Connect the input power supply to the V
IN
and GND
terminals on the left-hand side of the board. Do not
increase V
IN
over 10V or the Zener, D2, will be
damaged. Select the appropriate position of jumper
JP1 for the V
IN
voltage (position “V
IN
< 5V” for V
IN
< 4.5V only).
• Connect the load between the V
OUT
and GND
terminals on the right side of the board.
• The RUN/SS pin can be left unconnected. To shut
down the LTC1627, tie this pin to GND.
• Set the desired output voltage with jumper JP2, as
shown in Figure 2 and Table 1.
1.8V
2.5V
Table 1. Maximum Allowable Input Voltage vs Selected
Output Voltage and JP1 Position
JP2 OUTPUT VOLTAGE
1.8V
2.5V
2.9V
3.3V
N/A
Note 1:
The silkscreen label “< 5V” on the demo board is a simplified
notation. The actual voltage should be
≤
4.25V.
JP2
MAXIMUM V
IN
FOR JP1 POSITION
“≥ 5V”
8.5V
8.5V
8.5V
8.5V
“< 5V” (Note 1)
4.5V
4.5V
4.5V
4.5V
2.9V
3.3V OPEN
DC195 • F02
Figure 2. Output Voltage Selection (JP2)
(3.3V Position Shown)
OPERATIO
The circuit in Figure 1 highlights the capabilities of the
LTC1627. The application circuit is set up for a variety of
output voltages. Output voltages from 1.8V to 3.3V or user
programmable voltages can be obtained by selecting the
appropriate jumper position.
The LTC1627 is a monolithic synchronous step-down
switching regulator using a fixed-frequency architecture.
Burst Mode operation provides high efficiency at low load
currents. Operating efficiencies typically exceed 90% over
two decades of load current range. 100% duty cycle
provides low dropout operation, which extends operating
time in battery-operated systems.
Do not use small spring-clip leads when testing this
circuit. Small spring-clip leads are very convenient for
small-signal bench testing and voltage measurements,
but should not be used with this circuit. Soldered wire
connections are required to properly ascertain the perfor-
mance of the PC board.
4
U
This demonstration board is intended for the evaluation of
the LTC1627 switching regulator IC and was not designed
for any other purpose.
The operating frequency of this demo circuit is 350kHz,
the frequency of the LTC1627’s internal oscillator. For
higher frequencies, SYNC/FCB (E1) can be synchronized
with an external clock. Burst Mode operation is automati-
cally disabled when the SYNC/FCB pin is externally driven.
Grounding SYNC/FCB also disables Burst Mode opera-
tion, potentially reducing noise and interference.
Soft start is provided by an external capacitor, C
SS
, which
can be used to properly sequence supplies. The maximum
operating current level is 0.5A.
This demo board is optimized for 3.3V outputs and 5V
input. Output voltages from 1.8V to 3.3V are available by
selecting the appropriate jumper position of JP2. For other
output voltages, select the OPEN (E) position and add an
DEMO MANUAL DC195
NO-DESIGN SWITCHER
OPERATIO
V
IN
1.5µA
SLOPE
COMP
SYNC/FCB
8
0.4V
OSC
6 V
IN
0.6V
–
6Ω
V
FB
3
+
–
V
IN
FREQUENCY
SHIFT
EN
0.8V
REFERENCE
UVLO
TRIP = 2.5V
SHUTDOWN
appropriate resistor value in the space provided. The
output voltage must never exceed 3.3V because the output
capacitor may be damaged. The input supply can range
from 2.65V to 8.5V.
Main Control Loop (Refer to Functional Diagram)
The LTC1627 uses a constant-frequency, current mode
step-down architecture. Both the main and synchronous
switches, consisting of top P-channel and bottom
N-channel power MOSFETs, are internal. During normal
operation, the internal top power MOSFET is turned on
U
BURST
DEFEAT Y
X
Y = “0” WHEN X IS A CONSTANT “1”
V
IN
V
IN
+
0.8V
–
SLEEP
0.12V
+
EA
+
BURST
–
2.25µA
V
IN
RUN/SS 2
RUN/
SOFT START
1 I
TH
–
I
COMP
+
S
R
Q
Q
7 V
DR
ANTI
SHOOT THRU
–
OVDET
0.86V
+
SWITCHING
LOGIC
AND
BLANKING
CIRCUIT
5 SW
0.8V
–
FCB
I
RCMP
+
–
4 GND
DC195 • FD
+
Figure 3. Functional Block Diagram
during each cycle when the oscillator sets the RS latch,
and turned off when the current comparator, I
COMP
, resets
the RS latch. The peak inductor current at which I
COMP
resets the RS latch is controlled by the voltage on the I
TH
pin, which is the output of error amplifier EA. The V
FB
pin
allows EA to receive an output feedback voltage from an
external resistive divider. When the load current increases,
it causes a slight decrease in the feedback voltage relative
to the 0.8V reference, which, in turn, causes the I
TH
voltage
to increase until the average inductor current matches the
new load current. While the top MOSFET is off, the bottom
5
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