LINEAR TECHNOLOGY
DESCRIPTION
PRE-RELEASE
DEMO MANUAL DC(1775)
LTC1775 High Power
No R
SENSE
Stepdown Controller
efficiencies in excess of 95% are
readily achieved without sacrificing
the advantages of current mode
control such as inherent current
limiting, excellent rejection of line
transients, and simple compensation.
At low output currents, the
LTC1775 automatically changes to
Burst Mode
TM
operation to reduce
switching losses and maintain high
operating efficiency. Additionally,
the supply current can be shut down
to less than 20uA to maximize battery
life in portable applications. This
board is intended for applications
such as notebook computers,
automotive electronics, and
distributed power systems.
Gerber
files for this circuit board are
available. Call the LTC factory.
Demonstration Circuit (1775) is
a constant frequency stepdown (buck)
regulator for high power applications
using the LTC1775 No R
SENSE
controller.
The regulator delivers up to 10A at
fixed output voltages of 3.3V and 5V.
The output voltage can also be
adjusted with an external feedback
divider from 1.19V up to 12V. Input
voltages can range from 4.5V up to
28V.
The LTC1775 controller uses a
current mode, constant frequency
architecture to switch a pair of N-
channel power MOSFETs. Current mode
control is provided without using a
sense resistor by monitoring the
voltage drop across the MOSFET
switches in order to determine the
inductor current. By eliminating the
power loss in the sense resistor,
PERFORMANCE SUMMARY
SYMBOL
V
IN
I
OUT(MAX)
V
OUT
∆V
OUT(RIPPLE)
∆V
OUT(LOADREG)
∆V
OUT(LINEREG)
I
Q
I
EXTVCC
V
RUN/SS
f
Operating Temperature Range 0C to 50C
VALUE
4.5V to
28V
10A
3.3V, 5V
1.19V to
12V
50mV
100mV
-0.2%
0.05%
300uA
15uA
550uA
1.4V
150kHz
CONDITIONS
Input Voltage Range (Maximum input voltage limited by external MOSFET
and input capacitor)
Maximum Output Current
Output Voltage (Jumper selectable)
Output Voltage (Adjustable, limited by output capacitor)
Output Voltage Ripple at V
IN
=10V, V
OUT
=5V, I
OUT
=5A
Output Voltage Ripple at V
IN
=10V, V
OUT
=5V, I
OUT
=0.5A (Burst Mode)
Load Regulation, I
OUT
=0A to 10A, Continuous Mode
Line Regulation, V
IN
=4.5V to 20V, Continuous Mode
Supply Current at V
IN
=10V, I
OUT
=0A, FCB=INTV
CC
(Burst Mode), EXTV
CC
=5V
Supply Current in Shutdown at V
IN
=10V
EXTV
CC
Pin Current at V
IN
=10V, I
OUT
=0A, FCB=INTV
CC
(Burst Mode), EXTV
CC
=5V
RUN/SS Pin Threshold
Switching Frequency, SYNC=0V
TYPICAL PERFORMANCE CHARACTERISTICS AND BOARD PHOTO
CBU:manual.doc
December 17, 2002
LINEAR TECHNOLOGY CONFIDENTIAL
1
LINEAR TECHNOLOGY
PRE-RELEASE
DEMO MANUAL DC(1775)
PACKAGE AND SCHEMATIC DIAGRAMS
TOP VIEW
(Package Drawing)
S PACKAGE
16-LEAD PLASTIC SO
(Schematic Drawing)
CBU:manual.doc
December 17, 2002
LINEAR TECHNOLOGY CONFIDENTIAL
2
LINEAR TECHNOLOGY
PARTS LIST
PRE-RELEASE
DEMO MANUAL DC(1775)
This parts list is out of date, use latest list from J. Larson.
REFERENCE
DESIGNATOR
C
1
C
B
C
C1
C
C2
C
F
C
IN1
-C
IN3
C
OUT1
, C
OUT2
C
OUT3
C
SS
C
VCC
D1
D
B
D
Z
E1-E9
JP1-JP4
JP5-JP6
JP7
JP1-JP7
L1
M1, M2
Q
1
, Q
3
, Q
5
Q
2
, Q
4
Q
5
R
1
R
2
R
3
R
C1
R
F
R
Z
U1
QUANTITY
1
1
1
1
1
3
2
1
1
1
1
1
1
9
4
2
1
7
1
2
3
2
3
1
1
1
1
1
1
1
PART NUMBER
DESCRIPTION
Optional
0.47uF 16V Y5V Chip Capacitor
2.2nF 50V 10% NPO Chip Capacitor
220pF 50V 10% NPO Chip Capacitor
0.1uF 50V X7R Chip Capacitor
22uF 50V Y5U Chip Capacitor
270uF 16V 20% OS-CON Capacitor
10uF 16V 10% Chip Capacitor
0.1uF 16V X7R Chip Capacitor
4.7uF 16V 20% Tantalum Capacitor
1A 40V Schottky diode
100mA 30V Schottky diode
6.8V 20mA zener diode
Turret Terminal
2 Pin Header
3 Pin Header
4 Pin Header
Jumper
4.8uH 10A Inductor
N-channel MOSFET
NPN Transistor
PNP Transistor
NPN Transistor
11kΩ 1/10W 1% Chip Resistor
100kΩ Potentiometer
10Ω 1/10W 1% Chip Resistor
10kΩ 1/10W 5% Chip Resistor
1Ω 1/10W 5% Chip Resistor
1.5kΩ 1/10W 5% Chip Resistor
VENDOR
TELEPHONE
?
08055C222
08055A221
0805YC104MAT
THCR70E1H226
ZT
16SP270M
GRM235Y5V106
Z
0805YC104MAT
TAJA475H020R
MBRS140T3
CMDSH-3
CMPZ5253B
2501-2
?
?
?
CC1J2MM-138-
G
ETQPAF4RH
SUD50N03-10
FMMT619
FMMT720
FCX619
CR10-113JM
3266 Y-1-104
CR10-100JM
CR10-103JM
CR10-1R0JM
CR10-152JM
LTC1775CS
AVX
AVX
AVX
AVX
United
Chemi-con
Sanyo
Murata
AVX
AVX
Motorola
Central
Central
Mill-Max
Comm Con
Comm Con
Comm Con
Comm Con
Panasonic
Siliconix
Zetex
Zetex
Zetex
Tad
Bourns
Tad
Tad
Tad
Tad
LTC
CBU:manual.doc
December 17, 2002
LINEAR TECHNOLOGY CONFIDENTIAL
3
LINEAR TECHNOLOGY
QUICK START GUIDE
Please follow the procedure below to
quickly and easily configure the
demonstration circuit for
evaluation.
1. Refer to Figure 4 for the correct
arrangement of measurement
equipment.
2. Select the desired output voltage
with the V
PROG
pin jumper JP7. The
upper position (5V) sets the output
to 5V and the middle position (3.3V)
sets the output to 3.3V. Placing the
jumper JP7 in the lower (12V)
position and removing the jumper JP3
(ADJ BYPASS) makes the output
adjustable from 1.2V to 12V with the
potentiometer R2.
3. Set the SYNC pin jumper JP6 to
the lower position (150K) for 150KHz
operation.
4. Set the FCB pin jumper JP5 to the
upper position (BURST) to enable
Burst Mode operation.
5. Remove the EXTV
CC
supply jumper
(JP4) so that the LTC1775 supplies
its own gate drive.
6. Check that the gate drive jumpers
JP1 and JP2 are in place. This
disables the optional gate drive
buffers.
7. Connect the input power supply
across the IN terminal (E6) and the
input GND terminal (E7) located at
the bottom of the board. Be careful
not to apply input voltages above
28V or else the MOSFETs may be
damaged.
8. Connect the load between the OUT
terminal (E9) and the output GND
terminal (E8) located on the right
side of the board.
PRE-RELEASE
DEMO MANUAL DC(1775)
CBU:manual.doc
December 17, 2002
LINEAR TECHNOLOGY CONFIDENTIAL
4
LINEAR TECHNOLOGY
OPERATION
(Insert text A)
An optional 6V EXTV
CC
supply derived
from the input voltage is provided
on the board. This can be connected
using jumper JP4.
(Insert text B)
External Driver Buffers
The LTC1775 drivers are adequate for
driving up to about 30nC into the
MOSFET switches. When using large
single, or multiple, MOSFET
switches, external buffers may be
needed to provide additional gate
drive capability. The demonstration
circuit includes optional external
bipolar driver buffers. These are
bypassed when jumpers JP1 and JP2
are in place. By removing these
jumpers, the external buffers become
active. This makes it easy to
compare the converter behavior and
efficiency with and without external
buffers. Note that the bipolar
drivers reduce the signal swing at
the MOSFET gates. Thus, it is
recommended that the 6V EXTV
CC
circuit be used (set jumper JP4)
when the driver buffers are active.
PRE-RELEASE
DEMO MANUAL DC(1775)
CBU:manual.doc
December 17, 2002
LINEAR TECHNOLOGY CONFIDENTIAL
5
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