DC1432A - Demo Manual

DEMO CIRCUIT 1432A
LTC3851AEUD/
LTC3851AEUD-1
QUICK
START GUIDE
LTC3851AEUD/
LTC3851AEUD-1
SYNCHRONOUS BUCK CONVERTER
DESCRIPTION
Demonstration circuit 1432A is a synchronous buck
converter featuring the LTC3851AEUD/ LTC3851AEUD-1.
The demo circuit is available in two versions. DC1432A-A
is configured with LTC3851AEUD which provides ISET
function, while the DC1432A-B is configured with
LTC3851AEUD-1 which provides PGOOD function.
The main features of the board include an internal 5V
linear regulator for bias and a Mode selector that allows
the converter to run in Forced CCM Mode, Pulse Skip
Mode or Burst Mode operation. Synchronization to an
external clock is also possible on this board.
The demo circuit has an optional DCR sense circuit that
allows using the inductor’s DCR as the current sensing
Table 1. Performance Summary (TA=25°C)
PARAMETER
Input Supply Range
Output Voltage Range
Nominal Switching Frequency
Full Load Efficiency
(See Figure 3 for efficiency curves)
element to save cost, footprint and improve full load efficiency about 2%.
The LTC3851AEUD/ LTC3851AEUD-1 datasheet gives a
complete description of these parts, operation and application information and must be read in conjunction with
this quick start guide for Demonstration circuit 1432A.
Design files for this circuit board are available. Call
the LTC factory.
L, LTC, LTM, LT, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are registered
trademarks of Linear Technology Corporation. Adaptive Power, C-Load, DirectSense, Easy
Drive, FilterCAD, Hot Swap, LinearView, µModule, Micropower SwitcherCAD, Multimode
Dimming, No Latency ∆Σ, No Latency Delta-Sigma, No RSENSE, Operational Filter, PanelProtect, PowerPath, PowerSOT, SmartStart, SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT,
UltraFast and VLDO are trademarks of Linear Technology Corporation. Other product names
may be trademarks of the companies that manufacture the products.
CONDITIONS
MIN
4.5
1.47
VIN = 12V, ILOAD = 15A
VIN = 12V, VOUT = 1.5V, ILOAD = 15A
TYP
1.5
350
88.9
MAX
14
1.53
UNITS
V
V
kHz
%
QUICK START PROCEDURE
Demonstration circuit 1432A is easy to set up to evaluate
the performance of the LTC3851AEUD/ LTC3851AEUD-1.
Refer to Figure 1 for proper measurement equipment
setup and follow the procedure below:
NOTE. When measuring the input or output voltage ripple, care must be
taken to avoid a long ground lead on the oscilloscope probe. Measure the
input or output voltage ripple by touching the probe tip directly across the
Vin or Vout and GND terminals. See Figure 2 for proper scope probe
technique.
1. Place jumpers in the following positions:
FREQ/PLLFLTR 350kHz
RUN On
MODE/PLLIN CCM
2. With power off, connect the input power supply to
Vin and GND.
3. Turn on the power at the input.
NOTE. Make sure that the input voltage does not exceed 14V.
1
LTC3851AEUD/ LTC3851AEUD-1
4. Check for the proper output voltage. Vout = 1.470V
to 1.530V
NOTE. If there is no output, temporarily disconnect the load to make
sure that the load is not set too high.
5. Once the proper output voltages are established, adjust the loads within the operating range and observe
the output voltage regulation, ripple voltage, efficiency and other parameters.
6. Different operating modes can be evaluated by
changing the position of MODE/PLLIN jumper and
are discussed in the next section.
Iin
A
+
V
Vin
+
Vin supply
-
Vout
+
V
Iout
-
A
+
Vout
load
-
Figure 1. Proper Measurement Equipment Setup
GND
VIN
Figure 2. Measuring Input or Output Ripple
2
LTC3851AEUD/ LTC3851AEUD-1
FREQUENCY SYNCHRONIZATION AND MODE SELECTION
Demonstration circuit 1432A’s Mode selector allows
the converter to run in Forced CCM Mode, Pulse Skip
Mode or Burst Mode operation by changing position of
MODE/PLLIN jumper. For synchronizing to an external
clock source, FREQ/PLLFLTR jumper needs to be
placed at “EXTCLK” position and MODE/PLLIN jumper
needs to be removed. Apply the external clock from the
MODE/PLLIN turret to GND. Refer to Table 2 and to the
data sheet for more details.
Table 2. Mode Selection and Synchronizing Operation Options
CONFIGURATION
Forced CCM Mode Operation
Pulse Skip Mode Operation
Burst Mode Operation
Synchronize to Ext. clock (Ext. clock apply to MODE/PLLIN turret)
MODE/PLLIN JUMPER
“CCM”
“P.S.”
“BURST”
Remove Jumper
FREQ/PLLFLTR JUMPER
“350K”
“350K”
“350K”
“EXTCLK”
RAIL TRACKING
Demonstration circuit 1432A is configured for an on
board soft start circuit. The soft start ramp rate can be
adjusted by changing the value of C24. Demonstration
Table 3. Output Tracking Options
CONFIGURATION
Soft Start Without Tracking (Default)
Vout Equals External Ramp
Vout Tracking Scaled External Ramp
circuit 1432A can also be modified to track an external
reference. Refer to Table 3 for tracking options and to
the data sheet for more details.
R32
R35
0Ω
OPEN
0Ω
OPEN
Resistor Divider
C24
0.1μF
OPEN
OPEN
TRK/SS PIN
OPEN
External Ramp
External Ramp
OPTIONAL INDUCTOR DCR CURRENT SENSING
Demonstration circuit 1432A provides an optional circuit for Inductor DCR Current Sensing. Inductor DCR
Current Sensing uses the DCR of the inductor to sense
the inductor current instead of discrete sense resistors.
The advantages of DCR sensing are lower cost, reduced board space and higher efficiency, but the disTable 4. Optional Inductor DCR Current Sensing
CONFIGURATION
Current Sense Resistor (Default)
Inductor DCR Current Sensing
RSNSE
2mΩ, 1W
0Ω Copper
advantage is a less accurate current limit. If DCR sensing is used, be sure to select an inductor current with a
sufficiently high saturation current or use an iron
powder type. Refer to Table 4 for Optional Inductor
DCR Current Sensing setup and to the datasheet for
more details.
R10
100 Ω
OPEN
R9
100 Ω
OPEN
R1
OPEN
0Ω
C30
1nF
100nF
R27
OPEN
2k Ω
3
LTC3851AEUD/ LTC3851AEUD-1
Demonstration Circuit 1432A (LTC3851AEUD/LTC3851AEUD-1)
Test Efficiency
95
90
Efficiency (%)
85
80
75
Vin=4.5V CCM
Vin=12V CCM
70
Vin=14V CCM
65
0
2
4
6
8
10
Load Current (A)
12
14
16
Figure 3. Efficiency Curve for Demonstration Circuit 1432A
Demonstration Circuit 1432A (LTC3851AEUD/LTC3851AEUD-1)
Test Efficiency
95
90
Efficiency (%)
85
80
75
Vin=12V Current Sensing Resistor
70
Vin=12V Inductor DCR Sensing
65
0
2
4
6
8
10
Load Current (A)
12
14
Figure 4. Efficiency Curve for Demonstration Circuit 1432A with Optional Inductor DCR Current Sensing
4
16
[1]
C26
LTC3851AEUD-1
-B
100K
OPT
R42
OPT
U1
OPT
C29
R38
49.9K
1%
3 50K
C24
R32 0
OPT
R42
[1]
ILIM
1K
R43
PGOOD
ISET
E9
INTVCC
R41
0
R39
43.2K
1%
OPT
R35
0.1uF 10V
JP1
3
R46
7
4
3
2
1
C20
1nF
10nF
C22
ILIM
FB
ITH
TK/SS
RUN
U1
[1]
200K 1%
JP3
3
4
B URST P .S .
MODE/PLLIN
2
16
INTVCC
E XT CL K R31
FREQ/PLLFLTR
1
VIN
VOUT
C32
470pF
C28
OPT
R48
OPT
R47
97.6K 1%
R30
R40
6.49K
1%
3300pF
LTC3851AEUD
OPT
C23
3
OFF
-A
E9
E2
E1
JP2
ON
1
RUN
ASSY
[1]
TRK/SS
RUN
E4
2
MODE/PLLIN
2
14
R45
OPT
OPT
10
9
11
12
R44
1nF
C30
INTVCC
BG
VIN
BOOST
100
C31
4.7uF
10V
R9
2.2
R37
0
R36
3
7
8
C25
0.1uF
10V
100
2
4
R10
C27
2.2uF
10V
C19
1uF
BG
TG
Q5
OPT
Si4816BDY
VIN
5
6
1
1
GND
8
13
TG
15
5
FREQ/PLLFLTR
GND
17
MODE/PLLIN
SENSE-
SW
SW
TG
CMDSH-3
2
BG
VIN
INTVCC
D2
INTVCC
1
SW
CIN4
OPT
4
4
5
Q1
RJK0305DPB
Q2
OPT
4
Q4
OPT
4
Q3
RJK0329DPB
1
2
3
5
1
2
3
5
1
2
3
CCM
SENSE+
6
5
1
2
3
INTVCC
CIN3
22uF
25V
OPT
OPT
C18
R1
OPT
R29
OPT
R27
0.4uH
CIN5
OPT
OPTI ONAL DCR
SENSI NG
L1
CIN6
22uF
25V
CIN7
OPT
0.002 OHM
RSNSE
VIN
COUT3
47uF
6.3V
+ COUT1
330uF
2.5V
VOUT
+ CIN1
150uF
16V
E8
J4
+ COUT2
330uF
2.5V
J3
E7
E6
J2
J1
E5
GND
GND
1.5V / 15A
VOUT
VOUT
GND
GND
4.5V - 14V
VIN
VIN
LTC3851AEUD/ LTC3851AEUD-1
Figure 5. Demonstration Circuit 1432A Schematic
5
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