DC1381A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1381A
LOW QUIESCENT CURRENT, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER
LTC3857EUH/LTC3858EUH
DESCRIPTION
Demonstration circuit 1381A is a Low Quiescent
Current, Dual Output Synchronous Buck Converter featuring the LTC3857EUH/LTC3858EUH.
The circuit is single sided layout, while the package style for the LTC3857/8EUH is a 32 lead
(5mm x 5mm) QFN package
The main features of the board include rail tracking (LTC3857EUH only), an internal 5V linear regulator for bias, RUN pins for each output, a
PGOOD signal (CH1 only) and a Mode selector
that allow the converter to run in CCM, pulse skip
or Burst Mode operation. Synchronization to an
external clock is also possible.
Two versions of the board are available. DC1381A-A is for the LTC3857EUH, while the
DC1381A-B is for the LTC3858EUH. The
Table 1.
LTC3857EUH offers lower quiescent current and
smaller burst mode ripple, while the LTC3858EUH
offers latch-off protection and increased burst
mode efficiency.
The wide input voltage range of 4.5V to 36V is
suitable for automotive or other battery fed application where low quiescent current is important.
The LT3857EUH and LTC3858EUH datasheets
give a complete description of these parts, operation and application information. The datasheets
must be read in conjunction with this quick start
guide for demo circuit 1381A.
Design files for this circuit board are available.
Call the LTC factory.
Burst Mode is a trademark of Linear Technology Corporation
Performance Summary (TA = 25°C)
PARAMETER
CONDITION
VALUE
#
Minimum Input Voltage
4.5V
Maximum Input Voltage
36V
Output Voltage VOUT1
VIN = 4.5V to 36V, IOUT1 = 0A to 5A
3.3V ±2%
Output Voltage VOUT2
VIN = 9V to 36V, IOUT2 = 0A to 3A
8.5V ±2%
Nominal Switching Frequency
350kHz
VIN = 24V
VIN = 36V
VOUT1 = 3.3V, IOUT1 = 5A
92.5%* Typical
90.4%* Typical
VOUT2 = 8.5V, IOUT1 = 3A
96.6%* Typical
95.4%* Typical
Efficiency, DC1381A-A/B
See Figures 3 to 6 for efficiency curves
* Measured at bulk output capacitor
#
Minimum input voltage required for 8.5Vout regulation is 9Vin
QUICK START PROCEDURE
Demonstration circuit 1381A is easy to set up to
evaluate
the
performance
of
the
LTC3857EUH/LTC3858EUH. 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 probing directly across
the bulk Vin or Vout capacitor. See Figure 2 for
proper scope probe technique.
1.
Place jumpers in the following positions:
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1381A
LOW QUIESCENT CURRENT, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER
JP2
Burst Mode
JP3
On
JP4
JP5
On
JP6
SS
4.
NOTE: If
there is no output, temporarily disconnect the load to make sure that the load is not
set too high.
SS
2.
With power off, connect the input power supply
to Vin and GND.
3.
Turn on the power at the input.
NOTE: Make
Check for the proper output voltages.
Vout1 = 3.234V to 3.366V,
Vout2 = 8.330V to 8.670V
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 position of jumper JP3.
sure that the input voltage does not
exceed 26V.
Iout1
+
A
Vout1
Vout1
load
-
V
+
-
Iin
A
+
V
-
Vin
+
Vin supply
-
Vout2
load
+
-
V
+
Vout2
A
Iout2
Figure 1. Proper Measurement Equipment Setup
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1381A
LOW QUIESCENT CURRENT, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER
Figure 2. Measuring Input or Output Ripple Directly Across Bulk Capacitor
RAIL TRACKING
Demonstration circuit 1381 is setup for independent soft start without tracking. The soft start
ramp-rate is determined by the value of the SS
capacitors C1 and C23. This board can also be
operated in coincident tracking mode with either
Table 2.
output as master or both can slave an external
ramp Refer to Table 2 for tracking options and to
the data sheet for more details.
Output Tracking Options
TRACK/SS JUMPERS
CONFIGURATION
JP3
JP4
TERMINALS
TRACK1
TRACK2
Soft Start Without Tracking
Vout1
SS
Vout2
No connection / Don’t care
SS
No connection / Don’t care
Coincident Tracking:
Vout1 tracking External Ramp
TRACK
Vout2 tracking External Ramp
Connect external ramp
TRACK
Connect external ramp
Vout2 tracking Vout1
SS
TRACK
No connection / Don’t care
Connect to Vout1
Vout1 tracking Vout2
TRACK
SS
Connect to Vout2
No connection / Don’t care
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1381A
LOW QUIESCENT CURRENT, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER
INDUCTOR DCR SENSING AND RESISTOR SENSING
The DCR sense circuit uses the resistive voltage
drop across the inductor to estimate the current.
In contrast to the traditional sense resistor current feedback, the DCR sensing circuit offers
lower cost and higher efficiency, but results in
less accurate current limit due to the large variation of the inductor DC resistance. Furthermore,
this indirect current sensing method cannot detect inductor saturation and requires the use of
‘soft’ saturating inductors (such as powder iron)
Table 3.
resulting in increased core losses or ‘hard’ saturating inductors (such as ferrite) with sufficiency
high current ratings resulting in increased inductor size.
For modifying the demo board for DCR sensing,
please refer to Table 3. A full load efficiency improvement of between 0.25% – 0.75% is still
possible with optional DCR sensing, but since
the inductors are ferrite based, short circuit performance may be compromised.
DCR sensing component selection
REMOVE RSENSE NETWORK
DCR NETWORK
Vout1
R8, R9 = Open, R10 = Short
R28 = 1.37kΩ
R30 = 2.74kΩ
R29 = 0Ω
C6 = 0.47µF
Vout2
R20, R21 = Open, R17 = Short
R32 = 1.91kΩ
R31 = 1.54kΩ
R33 = 0Ω
C18 = 0.47µF
FREQUENCY SYNCHRONIZATION
Demonstration circuit 1381’s Mode selector allows the converter to run in CCM, pulse skip or
Burst Mode operation by changing position of
jumper JP2. For synchronizing to an external
clock source, remove jumper JP2 entirely and
apply the external clock signal to the
PLLIN/MODE pin. Please refer to datasheet for
details on external clock signal requirements.
4
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1381A
LOW QUIESCENT CURRENT, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER
LTC3857EUH
Figure 3. Typical Efficiency vs. Load Current for A-A board – 24Vin, 3.3Vout and 8.5Vout
LTC3857EUH
Figure 4. Typical Efficiency vs. Load Current for A-A board – 36Vin, 3.3Vout and 8.5Vout
5
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1381A
LOW QUIESCENT CURRENT, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER
LTC3858EUH
Figure 5. Typical Efficiency vs. Load Current for A-B board – 24Vin, 3.3Vout and 8.5Vout
LTC3858EUH
Figure 6. Typical Efficiency vs. Load Current for A-B board – 36Vin, 3.3Vout and 8.5Vout
6
TRACK2
14V MAX
5
3
1
E 15
1
2
3
OFF
RUN1
R22
R41
OPT
R40
OPT
JP8
60
90
120
VIN
R37
[1]
R35
[1]
OPT
C29
1
SS
0.1uF
C1
97.6K 1%
R24
3
2
R25
10K
1%
3
T RA CK
JP6
T RA CK 2
CLKOUT PHASE
INTVCC
3
OFF
OPT
C28
1
2
RUN2
JP4
0
3
INTVCC
R38
OPT
R7
JP5
T RACK1
T RACK
R3
11.5K
ON
35.7K
R2
INTVCC
R36
OPT
R34
OPT
VOUT2
VIN
BURS T M ODE
PULSE SK IP
CCM
2.2uF
JP3
0
INTVCC
OPT
R26
C19
ON
6
4
2
EXTVCC
JP2
M ODE
C22
4.7uF
10V
E3
E9
E 17
E4
E2
E 10
VOUT2
E 16
1
R4
0.1uF
C23
SS
1%
R18
102K
1%
57.6K
C15
VOUT1
R23
0
OPT
C6
ITH2
R21
0
*
*
EXTVCC
R13 2.2
R1
200K
C27
C16
0.1uF
R15 2.2
100pF
15
16
17
18
19
20
21
22
23
24
25
26
27
14
SNS2+
R20
0
1000pF
TG2
SW2
BOOST2
BG2
INTVCC
EXTVCC
PGND
VIN
BG1
BOOST1
SW1
TG1
PGOOD1
C18
TRACK/SS2
PHSMD
ILIM
CLKOUT
GND
RUN2
RUN1
SGND
PLLIN/MODE
FREQ
C26
100pF
*
R9
0
PGOOD2
1000pF
*
R8
0
TRACK/SS1
ITH1
VOUT2
12
13
3
28
4
33
8
7
6
5
2
29
30
[1]
U1
0
R6
C21
R19
976K
1%
47pF
3300pF
C14
R16 15K
4700pF
R11 8.2K C4
C3 22pF
182K 1%
R5
C2 10pF
R39
200K
D2
D3
SW2 SHT 2
TG2 SHT 2
C13
47uF
50V
R14 0
INTVCC
4
4
Q3
BSZ097N04LS
INTVCC
INTVCC
C12
0.1uF
CMDSH-4E
CMDSH-4E
10V
C11 4.7uF
0.1uF
C10
TG1 SHT 2
VIN
+
BG2 SHT 2
Q4
BSZ097N04LS
4
VIN
4
BG1
SHT 2
Q2
BSZ097N04LS
BSZ097N04LS
Q1
VIN
SW1 SHT 2
*
2
R28
OPT
OPT
R30
CDEP 105-3R2M
L1 3.2uH
SNS1+
SNS1-
R29
OPT
CDE P105-7R2M
L2 7.2uH
R32
OPT
OPT
R31
0.005
*
R10
*
R17
0.008
R33
OPT
SNS2-
SNS2+
4.7uF
50V
4.7uF
50V
GND
VIN
VIN
GND
GND
GND
10uF
16V
GND
GND
E14
COUT4
+ OPT
J6
8.5V / 3A
VOUT2
VOUT2
J5
E13
E6
J4
4.5V - 36V
J3
E5
E12
J2
3.3V / 5A
VOUT1
VOUT1
C20
COUT2
+ 68uF
10V
C7
+ C5
OPT
C17
+ COUT1
220uF
4V
J1
VOUT2
VIN
COUT3
100uF
6.3V
VOUT1
E11
NOTE: WHEN DCR SENSING IS IMPLEMENTED, SHORT R10 AND R17,
DO NOT STUFF R8,R9,R20 AND R21
OPTIONAL DCR SENSING:
]2
[
EXTVCC
SGND
CLKOUT
PLLIN / MODE
100K
R27
INTVCC
INTVCC
TRACK1
PGOOD2
2
PGOOD1
S NS 11
S NS 1-
S NS 1+
32
E1
1
4
5
6
7
8
1
2
3
31
V FB 1
VFB2
11
S N S 29
SN S2-
5
6
7
8
1
2
3
S NS 1+
S N S 2+
10
G
N
SI
N
SE
5
6
7
8
R
C
D
LA
N
IO
TP
O
1
2
3
G
N
SI
N
ES
1
2
3
R
C
D
LA
N
IO
TP
O
5
6
7
8
INTVCC
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1381A
LOW QUIESCENT CURRENT, DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER
9V
>
IN
V
N
IO
T
A
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U
G
E
R
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1
53
R
T
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O
K
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6
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83
C
T
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85
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C
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SA
A
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7
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