DC1479A - Demo Manual

DEMO CIRCUIT 1479A
QUICK START GUIDE
LTC3865EUH
DUAL 15A SYNCHRONOUS BUCK
CONVERTER with PIN SELECTABLE OUTPUTS
DESCRIPTION
Demonstration circuit 1479A is a dual output synchronous buck DC/DC converter featuring the
LTC3865EUH. The input voltage range is from 4.5V
to 14V. The outputs are 1.5V/15A and 1.2V/15A.
Each output voltage can be precisely programmed to
a preset value within 1% error with the VID pins. The
demo board uses a high density, two sided drop-in
layout. The package of LTC3865EUH is a small, low
thermal impedance 5mm x 5mm 32-Lead QFN.
The light load operation mode of the converter is determined with the MODE/PLLIN pin. Use JP3 jumper
to select burst mode, pulse skipping mode or forced
continuous mode operation. Switching frequency is
pre-set at about 500KHz. This frequency can be
Table 1.
modified by changing R7 value at the FREQ pin. The
converter can also be externally synchronized from
250kHz to 770kHz through MODE/PLLIN pin (SYNC
terminal on the board). The maximum current sense
threshold can be adjusted by connecting ILIM pin to
SGND, float or INTVcc (with optional R42 and R44).
To shut down a channel, force its RUN pin below
1.2V (Jumper: OFF). The power good output
(PGOOD terminal) is low when either channel output
exceeds +/-10% regulation window.
Design files for this circuit board are available. Call
the LTC factory.
Performance Summary (TA = 25°C)
PARAMETER
CONDITION
Input Voltage Range
VALUE
4.5V to 14V
Output Voltage, VOUT1
VIN = 4.5-14V, IOUT1 = 0A to 15A
1.5V ±1%
(Note)
Output Voltage, VOUT2
VIN = 4.5-14V, IOUT2 = 0A to 15A
1.2V ±1%
(Note)
Maximum Output Current, IOUT1
VIN = 4.5-14V, VOUT1 = 1.5V
15A
Maximum Output Current, IOUT2
VIN = 4.5-14V, VOUT2 = 1.2V
15A
Typical full load Efficiency, channel 1
VIN = 12V, VOUT1 = 1.5V, IOUT1 = 15A
85%
Typical full load Efficiency, channel 2
VIN = 12V, VOUT2 = 1.2V, IOUT2 = 15A
83.4%
Typical Switching Frequency
500kHz
Note: VOUT1, VOUT2 are measured directly on output capacitors Cout1 and Cout4.
1
LTC3865EUH
QUICK START PROCEDURE
Demonstration circuit 1479A is easy to set up to
evaluate the performance of the LTC3865EUH. Refer
to Figure 1 for the proper measurement equipment
setup and follow the procedure below:
Jumper positions:
JP1,2 (RUN1/RUN2): ON
JP3 (MODE): CCM
the (-) lead and the probe tip needs to touch the (+)
lead.
Note: 2. Do not apply load from Vo1+ to Vo1- or
from Vo2+ to Vo2- turrets. These are only intended
to conveniently measure the output voltage. Heavy
load currents may damage the sense traces.
To accurately measure the output voltages and efficiency, please directly measure Vout1 and Vout2 on
output capacitors Cout1 and Cout4.
1. With power off, connect the input power supply to Vin (4.5V-14V) and GND (input return).
2. Connect the load #1 between Vout1 and GND
(Initial load: no load); connect the load #2 between Vout2 and GND (Initial load: no load).
3. Connect the DVMs to the input and outputs.
4. Turn on the input power supply and check for
the proper output voltages. With current VID
pin setting, Vout1 should be 1.5V+/-1%; Vout2
should be 1.2V+/-1%.
5. Once the proper output voltages are established, adjust the loads within the operating
range and observe the output voltage regulation, ripple voltage and other parameters.
6. If necessary, change the resistor options on
VID pins for another output voltage according
to table 2.
Note: 1. When measuring the output or input voltage ripple, do not use the long ground lead on the
oscilloscope probe. See Figure 2 for the proper
scope probe technique. Short, stiff leads need to be
soldered to the (+) and (-) terminals of an output
capacitor. The probe’s ground ring needs to touch
2
LTC3865EUH
OUTPUT VOLTAGE PROGRAMMING
The output voltages of both channels can be programmed to preset values. There are two VID pins for
each channel: VID11, VID12 for Vout1, and VID21,
VID22 for Vout2. See Table 2 for details.
Table 2. Output voltage programming
VID11/VID21
VID12/VID22
VOUT1/VOUT2 (V)
INTVCC
INTVCC
5.0 (Vin > 5V)
INTVCC
FLOAT
3.3
INTVCC
GND
2.5
FLOAT
INTVCC
1.8
FLOAT
FLOAT
FLOAT
GND
1.5
GND
INTVCC
1.2
GND
FLOAT
1.0
GND
GND
1.1
0.6 or external divider
SINGLE OUTPUT / DUAL PHASE OPERATION
A single output / dual phase converter may be preferred for high output current applications. The benefits of single output / dual phase operation are lower
ripple current through the input and output capacitors, improved load step response and simplified
thermal design. To implement single output / dual
phase operation, make the following modifications:
Tie VOUT1 to VOUT2. Use a piece of
heavy copper foil if possible.
1.
2.
3.
Tie VFB1 to VFB2 by stuffing 0Ω at R50.
4.
Tie TRK/SS1 to TRK/SS2 by stuffing 0Ω
at R52.
5.
Tie RUN1 to RUN2 by stuffing 0Ω at
R55.
6.
Remove channel 2 ITH compensation
network (C44, R35) and float VID21,
VID22 pins.
Tie ITH1 to ITH2 by stuffing 0Ω at R49.
3
LTC3865EUH
RAIL TRACKING
Demonstration circuit 1479A is configured for independent turn-on of VOUT1 and VOUT2. The ramp-rate
for VOUT1 is determined by the TRK/SS1 cap at C2
and the ramp-rate for VOUT2 is determined by the
TRK/SS2 cap at C47. This board can be modified on
the bench to allow VOUT1 to track an external signal.
Table 3.
VOUT1 Tracking Options (1.5V)
CONFIGURATION
Soft Start Without Tracking (original board)
External Coincident Tracking
Table 4.
It can also be modified to allow VOUT2 to track
VOUT1 or to allow VOUT2 to track an external signal.
Tables 3 and 4 cover the rail tracking options for each
rail.
R3
0Ω
17.8kΩ
TRACK1 DIVIDER
R2
Not stuffed
20.0kΩ
TRK/SS1 CAP
C2
0.1uF
Not Stuffed
VOUT2 Tracking Options (1.2V)
CONFIGURATION
Soft Start Without Tracking (original board)
R36
0Ω
TRACK2 DIVIDER
R34
R37
Not stuffed
Not stuffed
TRK/SS2 CAP
C47
0.1uF
Coincident Tracking to VOUT1 (1.5V)
0Ω
10.0kΩ
20.0kΩ
Not Stuffed
External Coincident Tracking
10.0kΩ
Not stuffed
20.0kΩ
Not Stuffed
INDUCTOR DCR SENSING
Demonstration circuit 1479A provides an optional
circuit for DCR sensing. DCR 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 disadvantage 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. Tables
5 and 6 show an example of how to modify the
DC1479A for DCR sensing using these parameters:
VOUT1 = 1.5V / 15A
VOUT2 = 1.2V / 15A
VIN = 4.5V to 14V
Fsw = 500kHz, typical
L1,2 = Vishay IHLP-4040DZERR47M11
(0.47uH, DCR = 1.53mΩ typ, 1.68mΩ max)
ILIM = FLOATING (R42,R44 = OPEN)
4
LTC3865EUH
Table 5.
VOUT1 Configured as a 1.5V/15A Converter Using DCR Sensing or a Discrete Sense Resistor
CONFIGURATION
DCR Sensing
Discrete RSENSE
(original board)
Table 6.
RS1
Short with Cu
strip or very
short & thick
piece of wire
2mΩ
L1
IHLP4040DZERR47M11
IHLP4040DZERR47M11
RSENSE
FILTER
RESISTORS
SENSE
FIILTER
CAP
R29,R30
Open
100Ω
DCR FILTER/DIVIDER
RESISTORS
SENSE1- TO L1JUMPER
TOP
BOTTOM
C14
0.22uF
R45
1.40kΩ
R47
15.4kΩ
R61
0Ω
1nF
Open
Open
Open
VOUT2 Configured as a 1.2V/15A Converter Using DCR Sensing or a Discrete Sense Resistor
CONFIGURATION
DCR Sensing
Discrete RSENSE
(original board)
RS2
Short with Cu
strip or very
short & thick
piece of wire
2mΩ
L2
IHLP4040DZERR47M11
IHLP4040DZERR47M11
RSENSE
FILTER
RESISTORS
SENSE
FIILTER
CAP
DCR FILTER/DIVIDER
RESISTORS
TOP
BOTTOM
SENSE1- TO L1JUMPER
R39,R40
Open
C15
0.22uF
R51
1.40kΩ
R53
15.4kΩ
R62
0Ω
100Ω
1nF
Open
Open
Open
5
LTC3865EUH
Figure 1. Proper Measurement Equipment Setup
+
COUT
VOUT
-
GND
Figure 2. Measuring Output Voltage Ripple
6
LTC3865EUH
95
Efficiency (%)
90
85
1.5Vo
1.2Vo
80
75
70
0
3
6
9
12
15
Load current (A)
Figure 3. Efficiency vs load current (Vin=12V, 500kHz, CCM)
7
E4
PGOOD
EXTVCC
0.1uF
OPT
ITH1
100K
R46
220pF
15K
SHT 2 TRK/SS2
C42
R31
C41 1nF
1uF INTVCC
C47
C50
OPT
R34
0.1uF
C2
R37
OPT
R2
SHT 2
SHT 2 TRK/SS1
12K
R35
C43 220pF
ITH2
SHT 2
1nF
C44
R7 162K 1%
10K
4
JP3
30
29
27
12
6
3
RUN2
4
14
20
13
11
TRK/SS2 7
ITH2
ITH1
TRK/SS1 2
RUN1
3
2
VID11
PGOOD
EXTVCC
ILIM
RUN2
TRK/SS2
ITH2
ITH1
TRK/SS1
RUN1
FREQ
MODE/PLLIN
VID21
VFB1
VFB2
1. DO NOT APPLY LOAD FROM THE VO1+ TO VO1- OR FROM THE VO2+ TO VO2- TURRETS.
THESE ARE ONLY INTENDED TO KELVIN SENSE THE OUTPUT VOLTAGE ACROSS COUT1
AND COUT4.
NOTES: UNLESS OTHERWISE SPECIFIED,
SHT 2 VFB2
SHT 2 VID12
SHT 2 VID11
PGOOD
GND
E2
ILIM
E3
0
C1
OPT
R3
0
R1
R36 0
VOUT1
E9
E1
E10
RUN2
EXTVCC
SHT 2
SHT 2
TRK/SS2
TRK/SS1
SHT 2 RUN1
SHT 2 VID21
SHT 2 VID22
SHT 2 VFB1
SYNC
E19
MODE
P S BM CCM
1
INTVCC
1
V ID 22
28
5
V ID 12
v os e ns e1
U1
R27 0
VINF
R9
1nF
C14
R39
100
S2-
S2+
1nF
C15
0
R25
INTVCC
S1+
S1-
R29
100
R43 0
9
10
15
16
17
18
19
21
22
23
24
25
26
31
32
OPT
R33
SENSE2-
SENSE2+
SW2
TG2
BOOST2
PGND
BG2
INTVCC
VIN
BG1
BOOST1
TG1
SW1
SENSE1+
SENSE1-
LTC3865EUH
v os ens e2
8
R40
100
0.1uF
C17
R18
0
R30
100
SHT 2
VIN
S2-
SHT 2
S2+ SHT 2
0.1uF
C21
CMDSH-3
D2
4.7uF
C11
2.2
CMDSH-3
D1
0.1uF
C20
SW1 SHT 2
S1-
S1+ SHT 2
BG1 SHT 2
4
4
SW2 SHT 2
TG2 SHT 2
BG2 SHT 2
INTVCC
TG1 SHT 2
4
Q1
RJK0305DPB
4
VIN
Q3
RJK0305DPB
Q2
RJK0330DPB
Q4
RJK0330DPB
10uF
L1
0.47uH
L2
0.47uH
10uF
CIN2
CIN3
VIN
VL2-
VL1-
0.002
RS2
0.002
RS1
COUT4
100uF
6.3V
COUT1
100uF
6.3V
+ COUT5
220uF
4V
+ COUT2
220uF
4V
CIN1
180uF
16V
+ COUT6
220uF
4V
VOUT2
+ COUT3
220uF
4V
VOUT1
VIN
1
+
C36
4.7uF
6.3V
C32
4.7uF
6.3V
2
R4
5
6
7
8
1
2
3
SGND
33
5
6
7
8
1
2
3
5
6
7
8
1
2
3
5
6
7
8
1
2
3
INTVCC
VIN+
VIN-
GND
GND
VOUT1
1.5V / 15A
VO1+
VO2+
GND
VO2-
E14
J6
VOUT2
1.2V / 15A
J5
E13
VO1-
E12
J4
J3
E11
E6
J2
VIN
4.5V-14V
J1
E5
LTC3865EUH
8
BG1
TG2
SW2
BG2
SHT 1
SHT 1
SHT 1
SHT 1
SHT 1
SHT 1
SHT 1
4
Q8
OPT
4
Q6
OPT
4
4
OPT
R69
Q7
OPT
Q5
OPT
VID22
VID12
VID21
VID11
E17
E18
E15
E16
R67
10K
INTVCC
R70
10K
R68
OPT
INTVCC
R63
OPT
INTVCC
R66
OPT
R64
OPT
INTVCC
R65
10K
VID22
VID12
VID21
VID11
SW1
SHT 1
SHT 1
TG1
SHT 1
5
6
7
8
1
2
3
5
6
7
8
1
2
3
5
6
7
8
1
2
3
5
6
7
8
1
2
3
VIN
OPT
CIN4
OPT
CIN5
VIN
SHT 1 S2-
SW2
SHT 1 S1-
NOT E:
WHEN DCR SENSING IS
IM PLEM ENT ED, SHORT RSENSE1
A ND RS ENS E2. DO NOT S T UFF
R29,R30,R39 A ND R40
OPT IONAL DCR SE NSING
R45
OPT
R51
OPT
GND
GND
SW1
FLOAT
INTVCC
GND
FLOAT
INTVCC
GND
GND
GND
FLOAT
FLOAT
FLOAT
INTVCC
FLOAT
INTVCC
INTVCC
INTVCC
VID12/VID22
VID11/VID21
S2-
OPT
R53
S1-
OPT
R47
R62 OPT
OPT
R61
1.1
1.0
1.2
1.5
VL2-
S2+ SHT 1
VL1-
S1+ SHT 1
0.6 or external divider
1.8
2.5
3.3
5.0 (Vin > 5V)
VOUT1/VOUT2 (V)
JP2
3
1
2
RUN1
SHT 1
TRK/SS1
SHT 1
VFB1
OPT
OPT
R55
OPT
R52
RUN2
SHT 1
TRK/SS2
SHT 1
VFB2
ITH2
SHT 1
R49
OPT
R50
ITH1
SHT 1
R44
OPT
OPT
R42
OPT
OPT
OPT
R38
OPT
R28
R41
VIN
OPT
C38
OPT
R26
C48
OPT IONAL JUM PE RS FOR
SINGLE OUT PUT /DUAL PHA SE
OPERAT ION
INTVCC
ON
OFF
3
JP1
RUN2
OFF
ON
1
2
RUN1
VIN
ILIM SHT 1
RUN2 SHT 1
RUN1 SHT 1
LTC3865EUH
9
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