DC1569A - Demo Manual

DEMO CIRCUIT 1569A
LT3958
QUICK START GUIDE
LT3958
High Voltage Monolithic Boost Converter
DESCRIPTION
Demonstration circuit 1569A is a High Voltage Monolithic Boost Converter featuring the LT3958. The LT3958
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 11V to 40V and the
output voltage is 48V with 500mA over the entire input
voltage range.
The LT3958 has an internal n-channel 3.3A, 84V power
switch for high voltage, power, and efficiency. The dual
paddle package provides excellent heat dissipation for
the internal power switch. The LT3958 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.
For flyback converters, SENSE1 and SENSE2 pins are
available to filter the internal flyback current sense signal.
The demonstration circuit features small 1210 case size
ceramic input and output capacitors. The internal nchannel power switch provides efficiency as high as 94%
in typical boost applications with 24W output.
The LT3958 datasheet gives a complete description of
the part, operation and applications information. The
datasheet must be read in conjunction with this Quick
Start Guide for demonstration circuit 1569A. The LT3958
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’.
Design files for this circuit board are available. Call
the LTC factory.
L, LT are trademarks of Linear Technology Corporation.
PERFORMANCE SUMMARY Specifications are at TA = 25°C
PARAMETER
Input Supply Range
Output Voltage Programmed
Switching Frequency
Maximum Output current
Input Undervoltage Lockout (falling)
Input Turn-on Voltage (rising)
Efficiency
CONDITIONS
VIN = 11V-40V, ILOAD ≤ 500mA
RT = 41.2k
VIN = 11V-40V
R1=392k, R2=53.6k
R1=392k, R2=53.6k
VIN = 12V, ILOAD = 500mA
MIN
11
TYP
48
300
500
10.3
10.9
94.6
MAX
40
UNITS
V
V
kHz
mA
V
v
%
1
LT3958
QUICK START PROCEDURE
Demonstration circuit 1569A is easy to set up to evaluate
the performance of the LT3958. 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.
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 500mA 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 40V.
5. Check for the proper output voltage (48V).
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 1. Proper Measurement Equipment Setup
2
LT3958
TERMINAL OPTIONS
DC1569A 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 q 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 13V. 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 slightly
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
SGND
SGND
INTVCC
SYNC
EN/UVLO
GND
GND
E9
E2
E1
E5
E8
SYNC
NO SYNC
E10
E4
JP1
SYNC
3
2
1
C10
4.7uF
10V
0603
C8
0.01uF
0402
41.2k
1%
0402
R4
30
33
28
34
25
VC
RT
INTVCC
SYNC
EN/UVLO
C9
0.33uF
0603
R3
10k
0402
C14
(Opt)
0402
C2
2.2uF
100V
1210
INTVCC
R2
53.6k
1%
0402
C13
(Opt)
0402
300kHz
R1
392k
1%
0402
C1
2.2uF
100V
1210
27
VIN
U1
Sumida
L1
33uH
CDRH127/LDNP-330MC
LT3958EUHE
20
SW
VIN
11V - 40V
SS
32
SGND
24
SGND
4
GND
17
SGND
23
38
SW
GND
16
SGND
37
21
SW
GND
15
9
NC
NC
NC
NC
NC
FBX
SENSE1
SENSE2
SW
GND
13
GND
14
8
SW
GND
4
12
E3
36
35
10
2
1
31
6
3
3
C11
(Opt)
0402
D1
PDS360
R8
0 Ohm
0402
2
1
R7
15.8k
1%
0402
R5
464k
1%
0402
C12
(Opt)
0402
C3
2.2uF
100V
1210
C4
2.2uF
100V
1210
C5
2.2uF
100V
1210
C6
2.2uF
100V
1210
C7
2.2uF
100V
1210
E7
E6
GND
VOUT
48V @ 500mA
LT3958
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