DEMO MANUAL DC252
DESIGN-READY SWITCHER
LTC1736 5-Bit VID Constant
Frequency Synchronous DC/DC Converter
ciently. Output voltages can be configured according to
Intel mobile VID standards of 0.9V to 2.0V. An internal
power-good circuit monitors the output voltage for out-of-
regulation conditions. External frequency synchronization
is provided, as are three modes of operation: Burst Mode
TM
operation to reduce switching losses and maintain high
operating efficiencies, burst inhibit/forced continuous
mode and a low noise pulse-skipping mode that provides
constant frequency operation down to 1% maximum load
currents with low quiescent current. This results in a
power supply that has very high efficiency, low ripple and
fast transient response.
Gerber files for this circuit board
are available. Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.
DESCRIPTIO
Demonstration Circuit DC252 is designed for mobile 5-bit
VID-programmed notebook CPU applications using the
LTC
®
1736 switching regulator controller. A high perfor-
mance, constant frequency current mode architecture
generates a precise low voltage CPU core supply. Protec-
tion features include an externally defeatable overcurrent
latchoff and internal current foldback for overload condi-
tions. A soft-latched crowbar monitors the output voltage
for overvoltage protection. OPTI-LOOP
TM
compensation
allows the transient response to be optimized over a wide
range of output capacitance and ESR values. The circuit
was designed for a 5V to 24V input range but allows a 4.5V
to 28V range (limited by the external MOSFETs). Strong
output drivers easily handle large power MOSFETs effi-
PERFOR A CE SU
PARAMETER
Input Voltage Range
Output
CONDITIONS
(Maximum Input Voltage Limited By External MOSFET and Input Capacitor)
Output Voltage (Programmed with a 5-Bit Mobile VID Code)
Max Output Current (Continuous)
Max Output Current (Peak)
Typical Output Ripple Measured with 10MHz Bandwidth (Burst Mode Operation) I
O
= 100mA
Typical Output Ripple Measured with 10MHz Bandwidth (Continuous) I
O
= 5A
V
IN
Line Regulation 5V to 24V
TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTOS
Efficiency
100
EXTV
CC
= 5V
90
EFFICIENCY (%)
80
70
V
IN
= 24V
60
50
40
10mA
V
IN
= 5V
Component Side
V
IN
= 15V
100mA
1A
LOAD CURRENT (A)
10A
252 TA01
U
WW
U W
U
U W
ARY
VALUE
5V to 24V
0.9V to 2.0V
11.0A
12A
45mV
P-P
20mV
P-P
0.002%/V
Solder Side
1
DEMO MANUAL DC252
DESIGN-READY SWITCHER
PERFOR A CE SU
PARAMETER
I
OUT
I
Q
I
EXTVCC
V
RUN
Frequency
CONDITIONS
Load Regulation: No Load to Full Rated Output
Supply Current (Typical), No Load, V
IN
= 15V, FCB = INTV
CC
Supply Current in Shutdown (Typical), V
IN
= 15V
EXTV
CC
Pin Current, V
EXTVCC
= 5V, V
IN
= 10V, FCB = INTV
CC,
No Load, V
OUT
= 1.6V
Run Pin Threshold (Typical)
Operating Frequency (Typical), C
OSC
= 47pF
PACKAGE A D SCHE ATIC DIAGRA
JP1
BURST MODE
OFF
ON
INTV
CC
FCB/SYNC
E4
RUN
E3
JP2
LATCHOFF
R6
680k
CF1
0.1µF
U1
1
C
OSC
2
TG
24
R8
0Ω
C
B1
0.22µF
23
M2
FDS6680A
RF1
4.7Ω
C
IN1
22µF
30V
C
OSC1
47pF
C
SS1
0.1µF
C
C2
330pF R
C1
33k
C
C1
47pF
4
FCB
5
SGND
PGOOD
E1
JP3
PGOOD
INTV
CC
C1
47pF
9
C3
47pF
V
FB
10
V
OSENSE
11
VID0
12
VID1
6
PGOOD
R1
100k
C
S1
1000pF
7
SENSE
–
SENSE
+
RUN/SS
3
I
TH
BOOST
SW
LTC1736
V
IN
22
L1
1.2µH
R
CS1
0.004Ω
R
S1
10Ω
M1, M3
FDS6680A
2X
21
D1
CMDSH-3
INTV
CC
20
C2
19 4.7µF
+
BG
PGND
18
8
EXTV
CC
17
EXTV
CC
E2
VIDV
CC
16
VID4
15
VID3
14
VID2
13
LSB
JP4
B0
MSB
B4
R5, 10Ω
R2, 10Ω
247 F01
Figure 1. Demo Board Schematic
2
W
WW
W
U
U W
ARY
VALUE
– 0.3%
950µA
15µA
850µA
1.3V
270kHz
LTC1736CG24
TOP VIEW
C
OSC
RUN/SS
I
TH
FCB
SGND
+V
IN
E10
C
IN3
22µF
30V
GND
E9
PGOOD
SENSE
–
SENSE
+
V
FB
1
2
3
4
5
6
7
8
9
24 TG
23 BOOST
22 SW
21 V
IN
20 INTV
CC
19 BG
18 PGND
17 EXTV
CC
16 VIDV
CC
15 VID4
14 VID3
13 VID2
+
+
V
OSENSE
10
VID0 11
VID1 12
G PACKAGE
24-LEAD PLASTIC SSOP
V
OUT
0.9V TO 2V/11A
E7
V
OSNS
E11
C4
1µF
D2
MBRS340T3
+
CO1, CO2, C04, C06
180µF
4V
X4
GND
E8
DEMO MANUAL DC252
DESIGN-READY SWITCHER
PARTS LIST
REFERENCE
C1, C3
C2
C4
CC1
CC2
CB1
CF1, CSS1
CIN1, CIN3
CIN1, CIN3
CO1, CO2, CO4, CO6
CO1, CO2, CO4
CO3, CO5
C
OSC1
CS1
D1
D2
E1, GND, +V
IN
, V
OSNS
, V
OUT1
E2, E3, E4, E8, E9, GND,
+V
IN
, +V
OUT
JP1
JP2, JP3
JP4
L1
M1, M2, M3
R1
R2, R5, RS1
R6
R8
RC1
RCS1
RF1
U1
QUANTITY PART NUMBER
2
1
1
1
1
1
2
2
OPT
4
OPT
OPT
1
1
1
1
5
8
1
2
1
1
3
1
3
1
1
1
1
1
1
8
08055A470JAT1A
TACR475M010R
0805ZC105MAT1A
08055A470JAT1A
08055A331MAT1A
08055A224KAT1A
08055A104MAT1A
30SC22M
THCR70E1H2262T
EEFUE0G181R
T510X447MOO6AS
4SP820M
08055A470JAT1A
08055A102MAT1A
CMDSH-3
MBRS340T3
1593-2
1502-2
2802S-03-G2
2802S-02-G2
2202S-05-G2
ETQP6F1R2HFA
FDS6680A
CR10-104JM
CR10-100FM
CR10-685JM
CR10-0R0JM
CR10-333JM
LRF2010-01-R004F
CR10-470JM
LTC1736CG
CCIJ2mm-138-G
DESCRIPTION
47pF 50V 5% NPO Capacitor
4.7µF 10V 20% Tantalum Capacitor
1µF 10V 20% X7R Capacitor
47pF 50V 5% NPO Capacitor
330pF 50V 5% NPO Capacitor
0.22µF 50V 20% X7R Capacitor
0.1µF 50V 20% X7R Capacitor
22µF 30V OS-CON Capacitor
22µF 50V 20% Y5U Capacitor
180µF 4V SP Capacitor
470µF 6.3V Low ESR Tantalum Capacitor
820µF 4V OS-CON Capacitor
47pF 50V 5% NPO Capacitor
1000pF 50V 5% NPO Capacitor
BVR = 30V, 0.1A Schottky Diode
BVR = 40V, 3A Schottky Diode
Turret Terminal (Small)
Turret Terminal
2mm 3-Pin Header
2mm 2-Pin Header
2mm Dual 5-Pin Header
1.2µH Inductor
30V 0.013Ω N-Channel MOSFET
100k 1/10W 5% Chip Resistor
10Ω 1/10W, 1% Chip Resistor
680k 1/10W 5% Chip Resistor
0Ω 1/10W Chip Resistor
33k 1/10W 5% Chip Resistor
0.004Ω 1/2W 1% Resistor
4.7Ω 1/10W, 5% Chip Resistor
IC, LTC1736CG24
JUMPER
VENDOR
AVX
AVX
AVX
AVX
AVX
AVX
AVX
SANYO
MARCON
PANASONIC
KEMET
SANYO
AVX
AVX
CENTRAL
ON SEMICONDUCTOR
KEYSTONE
KEYSTONE
COMM CON
COMM CON
COMM CON
PANASONIC
FAIRCHILD
TAD
TAD
TAD
TAD
TAD
IRC
TAD
LTC
COMM CON
TELEPHONE
(843) 946-0362
(207) 282-5111
(843) 946-0362
(843) 946-0362
(843) 946-0362
(843) 946-0362
(843) 946-0362
(619) 661-6835
(847) 696-2000
(201) 348-7522
(408) 986-0424
(619) 661-6835
(843) 946-0362
(843) 946-0362
(516) 435-1110
(800) 282-9855
(718) 956-8900
(718) 956-8900
(626) 301-4200
(626) 301-4200
(626) 301-4200
(201) 348-7522
(408) 822-2126
(800) 508-1521
(800) 508-1521
(800) 508-1521
(800) 508-1521
(800) 508-1521
(361) 992-7900
(714) 255-9123
(408) 432-1900
(626) 301-4200
3
DEMO MANUAL DC252
DESIGN-READY SWITCHER
QUICK START GUIDE
This demonstration board is easy to set up to evaluate
the performance of the LTC1736. Please follow the
procedure outlined below for proper operation. Sol-
dered wire connections are required to properly evalu-
ate the performance of this switching regulator.
• Refer to Figure 2 for proper connection of monitoring
and measurement equipment.
• Connect the input power supply to the V
IN
and GND
terminals on the right-hand side of the board with
soldered connections. Do not increase V
IN
over 28V
or the MOSFET(s) WILL BE DAMAGED.
• Connect the load between the V
OUT
and GND termi-
nals on the right side of the board with soldered
connections.
• The RUN pin can be left unconnected. To shut down
the LTC1736, tie this pin to ground.
• If an external 5V supply is used, connect it to EXTV
CC
.
• Set the jumper JP1 so that FCB selects the desired
mode:
JP1
On
Off
Open
MODE
Burst Mode Operation, Connect PGood to FCB/Sync
Forced Continuous
Apply External Clock to FCB/Sync
• Jumper JP2 determines if the overcurrent latchoff is
enabled. With JP2 installed this function is disabled.
Remove JP2 to enable.
JP2
Installed
Removed
OVERCURRENT LATCHOFF
Disabled
Enabled
• Active loads can cause confusing results. Refer to the
active load discussion in the Operation section.
A
+V
IN
• Set jumper JP4 for the desired output voltage. (See
Table 1.)
VID CPU POWER CONVERTER
RUN
OPTIONAL EXTERNAL
HIGH FREQUENCY
SOURCE CONNECTION
JP2 LATCHOFF
+
–
I
IN
+
–
V
IN
FCB/SYNC
OFF
ON
PGOOD
JP1 BURST
JP4
GND
V
O
PROG
B4
V
OSNS
+V
OUT
V
OUT
GND
EXT CLOCK
(REMOVE JP1 IF USED)
EXTV
CC
JP3
PGOOD
B0
–
LOAD
+
I
OUT
A
GND
LTC1736CG
DEMO CIRCUIT DC252A
(408) 432-1900
Figure 2
OPTIONAL REMOTE
V
OUT
SENSE CONNECTION
252 F02
I TRODUCTIO
The circuit in Figure 1 highlights the capabilities of the
LTC1736.
The LTC1736 is a synchronous step-down switching
regulator controller that drives external N-channel power
MOSFETs using a fixed frequency architecture with OPTI-
LOOP compensation. OPTI-LOOP compensation effectively
removes the constraints placed on C
OUT
by other controllers
for proper operation (such as restrictions on very low
ESRs). Burst Mode operation provides high efficiency at
4
U
low load currents. Operating efficiencies typically exceed
80% over more than two decades of load current range.
Do not use spring clip leads when testing this circuit.
Soldered wire connections are required to properly test
the performance of the PC board.
This demonstration circuit is intended for the evaluation of
the LTC1736 switching regulator IC and was not designed
for any other purpose.
U
DEMO MANUAL DC252
DESIGN-READY SWITCHER
OPERATIO
The operating frequency is set by an external capacitor,
C
OSC1
, allowing maximum flexibility in optimizing effi-
ciency. In this application, the frequency is set to 270kHz.
A multifunction control pin, FCB, inhibits Burst Mode
operation (reducing noise and RF interference), as well as
allowing synchronization to an external oscillator.
Soft-start is provided by an external capacitor, C
SS1
,
which can be used to properly sequence supplies. The
operating current level is user programmable via an exter-
nal current sense resistor and is set to 11A. Short-circuit
current is limited to approximately 4A by internal current
foldback.
Measuring Voltage Regulation
When trying to measure voltage regulation, remember
that all measurements must be taken at the point of
regulation. This point is where the LTC1736’s control loop
looks for the information to keep the output voltage
constant. In this demonstration board it is located be-
tween Pin 5 (SGND) of the LTC1736 and the sense side of
R
S1
. This point corresponds to the V
OSNS
terminal of the
board. Output voltage test leads should be attached di-
rectly to this terminal. The load should be placed across
the V
OUT
(E7) and GND (E8) terminals. Measurements
should not
be taken at the end of test leads at the load; refer
to Figure 2 for the proper monitoring equipment configu-
ration.
This applies to line regulation (input to output voltage
regulation) as well as load regulation tests. In doing line
regulation tests, always look at the input voltage across
the input terminals.
Remote Output Voltage Sensing
Remote output voltage sensing can be accomplished by
connecting the V
OSNS
terminal with another wire directly
to the load. A 10Ω resistor, R
S1
, connects V
OUT
to V
OSNS
to avoid open sense conditions. Never under any circum-
stance connect the load to V
OSNS
!
Output Voltage Programming
The output voltage is digitally set to levels between 0.925V
and 2.00V using the voltage identification (VID) inputs B0
to B4 set by jumper JP4. The internal 5-bit DAC configured
U
as a precision resistor voltage divider sets the output
voltage in 50mV/25mV increments according to Table 1.
Table 1. VID Output Voltage Programming
B4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
B3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
B2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
B1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
B0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
V
OUT
(V)
2.000V
1.950V
1.900V
1.850V
1.800V
1.750V
1.700V
1.650V
1.600V
1.550V
1.500V
1.450V
1.400V
1.350V
1.300V
*
1.275V
1.250V
1.225V
1.200V
1.175V
1.150V
1.125V
1.100V
1.075V
1.050V
1.025V
1.000V
0.975V
0.950V
0.925V
**
Note:
*, ** Represents codes without a defined output voltage as
specified in Intel specifcations. The LTC1736 interprets these codes as a
valid input and produces output voltage as follows: [01111] = 1.250V,
[11111] = 0.900V.
5
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