DC1544A - Demo Manual

DEMO CIRCUIT 1544
LT3957
QUICK START GUIDE
LT3957
Boost, SEPIC, Flyback and Inverting Converter with 5A,
40V Switch
DESCRIPTION
Demonstration circuit 1544 is a Boost, SEPIC, Flyback
and Inverting Converter with 5A, 40V Switch featuring
the LT3957. The LT3957 can be configured as a boost,
flyback, SEPIC, and inverting converter, but the demonstration circuit is assembled as a boost. The input voltage range is 4.5V to 20V and the output voltage is 24V
with 600mA over the entire input voltage range.
datasheet must be read in conjunction with this Quick
Start Guide for demonstration circuit 1544A. The LT3957
is assembled in a 36-lead plastic UHE package with two
thermally enhanced pads for SW and GND. Proper board
layout is essential for both proper operation and maximum thermal performance. See the datasheet section
‘Layout Considerations’.
The LT3957 has an internal n-channel 5A, 40V power
switch for high voltage, power, and efficiency. The dual
paddle package provides excellent heat dissipation for
the internal power switch. The LT3957 current-mode
dc/dc converter features adjustable switching frequency,
soft-start, compensation, shutdown and undervoltage
lockout with hysteresis, and a feedback pin (FBX) that
can be used in both positive and negative applications. A
SYNC input can be used to synchronize the switching at
a frequency higher than the IC is programmed.
The demonstration circuit features small 1210 case size
ceramic input and output capacitors. The internal nchannel power switch provides efficiency as high as 95%
in typical boost applications with 14.4W output.
The LT3957 datasheet gives a complete description of
the part, operation and applications information. The
PARAMETER
Minimum Input Supply Voltage
Maximum Input Supply Voltage
Output Voltage Programmed
Switching Frequency
Guaranteed Maximum Output current
Input Undervoltage Lockout (falling)
Input Turn-on Voltage (rising)
Efficiency
Figure 1. DC1544A 12VIN Efficiency
Design files for this circuit board are available. Call
the LTC factory.
L, LT are trademarks of Linear Technology Corporation.
CONDITIONS
VIN = 4.5V-20V, ILOAD ≤ 600mA
RT = 41.2k
VIN = 4.5V-20V
R1=200k, R2=95.3k
R1=200k, R2=95.3k
VIN = 12V, ILOAD = 600mA
4.5
20
24
300
600
3.8
4.2
95
UNITS
V
V
V
kHz
mA
V
v
%
1
LT3957
QUICK START PROCEDURE
Demonstration circuit 1544 is easy to set up to evaluate
the performance of the LT3957. Refer to Figure 2 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.
1. Place jumpers in the following positions:
JP1 NO SYNC
2. With power off, connect the input power supply to
VIN and GND.
NOTE. Connect power to GND, not SGND.
3. Connect a load of 600mA or less to VOUT and GND
terminals (not SGND).
4. Turn on the power at the input.
NOTE. Make sure that the input voltage does not exceed 20V.
5. Check for the proper output voltage (24V).
NOTE. If there is no output, temporarily disconnect the load to make
sure that the load is not set too high.
6. Once the proper output voltage is established, adjust
the load and input within the operating ranges and
observe the output voltage regulation, ripple voltage,
efficiency and other parameters.
Figure 2. Proper Measurement Equipment Setup
2
LT3957
TERMINAL OPTIONS
DC1544A has both GND and SGND terminals. The schematic shows that the GND and SGND pins of the IC are
not tied together outside the IC. They are internally connected. It is important that power ground currents do not
run on the SGND components. SGND is used to terminate the signal ground components such as compensation and feedback. Input and output power as well as
input and output caps, catch diodes, etc. should all connect to the GND plane. The SGND terminals are provided
in case the customer would like to make signal ground
measurements, but they do not need to be used. Improperly connecting input power to the SGND terminal
results in noisy behavior of the IC.
EN/UVLO (enable / undervoltage lockout) is provided as
a terminal so that the part can quickly be placed in shutdown by tying EN/UVLO to GND. The EN/UVLO pin is
already being used as an undervoltage lockout threshold
for the VIN with resistors R1 and R2. Undervoltage lock-
out stops the IC from switching when VIN is too low, but
shutdown further reduces the VIN pin quiescent current
when EN/UVLO is tied directly to GND. It is okay to leave
the EN/UVLO terminal floating.
INTVCC is provided as a terminal to be able to power
INTVCC externally or to tie INTVCC directly to VIN when
VIN remains below 8V. It is okay to leave the INTVCC
terminal floating.
SYNC is provided as a terminal to be able to externally
synchronize the internal power switching frequency. If
SYNC is not used, the terminal should be left floating and
the JP1 position should be set at ‘NO SYNC’. If SYNC is
used, the switching frequency of SYNC should be 20%
higher than the programmed switching frequency of the
IC and the JP1 position must be set at ‘SYNC’. Please
see the datasheet for details regarding the use of SYNC
and the switching frequency range.
3
E9
E2
E1
E5
E8
SYNC
NO SYNC
E10
JP1
3
2
1
C9
4.7uF
10V
0603
300kHz
R1
200k
1%
0402
C13
OPT
0402
C2
2.2uF
50V
1210
C7
22nF
0402
0402
30
33
28
34
25
C8
0.33uF
0603
R3
6.8k
0402
R4 41.2k 1%
INTVCC
R2
95.3k
1%
0402
C12
OPT
0402
C1
2.2uF
50V
1210
NOTES: UNLESS OTHERWISE SPECIFIED,
1. ALL CAPACITORS AND RESISTORS ARE 0402.
2. ALL CAPACITOR VALUES ARE IN MICROFARADS.
3. ALL RESISTOR VALUES ARE IN OHMS.
SGND
SGND
INTVCC
SYNC
EN/UVLO
GND
GND
E4
VC
RT
INTVCC
SYNC
EN/UVLO
V IN
VIN
4.5V - 20V
U1
LT3957EUHE
SW
E3
27
SS
32
SG N D
37
SG N D
24
38
GND
17
SG N D
4
21
SW
GND
16
SG N D
23
20
SW
GND
15
9
NC
NC
NC
NC
NC
FBX
SENSE1
SENSE2
SW
GND
13
GND
14
8
SW
GND
4
12
L1 10uH
CDRH104RNP-100NC
36
35
10
2
1
31
6
3
3
C10
OPT
0402
D1
PDS360
R7
0
0402
2
1
R6
15.8k
1%
0402
R5
226k
1%
0402
C11
OPT
0402
C3
4.7uF
50V
1210
C4
4.7uF
50V
1210
C5
4.7uF
50V
1210
VOUT
C6
24V @ 600mA
4.7uF
50V
1210 E7
GND
E6
LT3957
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