DEMO MANUAL DC2375A
LTC3256EMSE
Dual Output 350mA Step-Down
Charge Pump with Watchdog Timer
DESCRIPTION
Demonstration circuit 2375A is a dual output 350mA
step-down charge pump with a watchdog timer featuring
the
LTC
®
3256EMSE.
The LTC3256 operates with a wide
input voltage range from 5.5V to 38V and is engineered
for diagnostic coverage in ISO262262 systems. The
LTC3256 can provide up to 350mA of output current from
a 12V battery with 2W less power dissipation than 2 ideal
LDOs. The DC2375A was populated with automotive grade
components for evaluation.
The LTC3256 data sheet gives a complete description of
the device, operation and application information. The data
sheet must be read in conjunction with this demo manual.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2375A
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
PERFORMANCE SUMMARY
SYMBOL
V
IN
V
IN
EMI
V
OUT5
V
OUT3
PARAMETER
V
IN
Input Voltage Range
V
IN
EMI Filter Input
OUT5 Output Voltage
OUT3 Output Voltage
Specifications are at T
A
= 25°C
CONDITIONS
MIN
5.5
5.5
0mA ≤ I
OUT5
≤ 100mA, V
IN
= 12V
0mA ≤ I
OUT3
≤ 100mA, V
IN
= 12V
4.85
3.200
5.05
3.30
TYP
MAX
38
38
5.19
3.366
UNITS
V
V
V
V
BOARD PHOTO
Figure 1.
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DEMO MANUAL DC2375A
TYPICAL APPLICATIONS
1µF
C
5.5V TO 38V
INPUT SUPPLY
V
IN
LTC3256
OUT3
1M
10µF
EN5
EN3
RT
WT
GND
PG5
PG3
RSTI
RST
WDI
REFOUT
DC2375A F02
10µF
C
–
5.0
4.5
POWER DISSIPATION (W)
5V OUTPUT
100mA MAX
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
+
OUTCP
OUT5
10µF
3.3V LOAD = 250mA
5V LOAD = 100mA
10µF
3.3V LDO OUTPUT
250mA MAX
IDEAL DUAL LDO
LTC3256
0.01µF
6.8nF
MICROCONTROLLER
INTERFACE
0.0
6
7
8
9
10 11 12
13 14 15 16
DC2375A F03
INPUT VOLTAGE (V)
Figure 2. High Efficiency Dual Output Power Supply
Figure 3. Power Dissipation vs Input Voltage
QUICK START PROCEDURE
Refer to Figure 4 for the proper measurement equipment
setup and jumper settings 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 V
IN
or
V
OUT
and GND terminals. See Figure 5 for proper scope
probe technique.
1. Make sure the jumper settings are as follows:
JP1: EN5 is on the HI position
JP2: EN3 is on the HI position
JP3: PULL-UP PWR is on the OUTCP position
JP4: RSTI is on the HI position
JP5: LED PWR is on the OUTCP position
JP6: CRT is set to INT position
JP7: CWT is set to the DIS position
2. Turn on and set PS1 to 12V.
3. Slowly increase the load OUT3 to 250mA and observe
the output ripple and the output voltage on OUT3.
4. Slowly increase the load OUT5 to 100mA and observe
the output ripple and the output voltage on OUT5.
5. Observe that I
IN
is approximately ½ the total output
current of 350mA plus the PG5, PG3 LED and I
Q
currents.
Note: Change the PULL-UP PWR and LED PWR jumpers
(JP3, JP5) to the V
EXT
position to observe I
IN
without
the added LED and resistor pull-up current. A 5V supply
can be connected to the V
EXT
terminals to power the
LEDs and pull-up the open drain outputs.
6. Decrease V
IN
to 8V and observe that I
IN
increased by
about 50mA. OUT5 is now powered by V
IN
.
7. Decrease V
IN
to 5.5V and observe that I
IN
has increased
to about another 125mA. The charge pump is now in
1:1 mode.
8. Press and hold the RST pushbutton switch, PB1, and
observe the RST LED illuminates.
9. Release the RST pushbutton.
10. Move the CWT jumper, JP7 from the DIS position to
the INT positions and observe that the RST LED pulses
on and off.
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DEMO MANUAL DC2375A
QUICK START PROCEDURE
11. Set a pulse generator with a 0 to 5V pulse and a 100ms
to 1 second period on the WDI pin and observe that
the RST LED extinguishes.
12. Decrease the pulse period below 35ms and observe
the RST LED pulses again.
13. Slowly increase the pulse period to above 2s and
observed that the RST LED stops pulsing when the
period is between about 60ms and 1.3s and starts to
pulse again above 2s.
14. Turn off the loads and supply when done evaluation.
NOTE: The reset time and watchdog time can be adjusted
using external capacitors if desired. Place the respective
jumper, CRT or CWT, to the EXT position. The external
capacitors populated on this board are 2.2nF to provide
the external time listed in the data sheet. Optional capacitor
pads, C10 and C13, are placed in parallel on the bottom
side of the board to allow additional capacitance to be
easily added to increase the RST or WDT times.
Figure 4. Proper Measurement Equipment Setup for DC2375A
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DEMO MANUAL DC2375A
QUICK START PROCEDURE
V
SIGNAL
GND
Figure 5. Measuring Input or Output Ripple
APPLICATIONS INFORMATION
Figure 6 illustrates how the input current changes as
the input voltage increases. Figure 7 illustrates how the
50
efficiency and power loss changes as the input voltage
increases.
40
150°C
25°C
–55°C
EFFICIENCY (%)
90
80
70
60
50
40
30
20
10
EFFICIENCY
I
OUT3
= 250mA
I
OUT5
= 100mA
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
LOSS
5
6
7
8
9
10 11 12 13 14 15
V
IN
(V)
DC2375A F07
POWER LOSS (W)
I
IN
(µA)
30
20
10
EN3=EN5=HIGH
5
6
7
8
9
10 11 12 13 14 15
V
IN
(V)
DC2375A F06
0.5
0.0
0
0
Figure 6. Input Operating Current
vs Input Voltage
Figure 7. Efficiency and Power Loss
vs Input Voltage
4
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DEMO MANUAL DC2375A
APPLICATIONS INFORMATION
Figure 8 and Figure 9 illustrate the radiated emission
performance without an EMI filter on the V
IN
input. These
tests were performed to CISPR 25 Class 5 peak limits
and were conducted using a 14V input, a 47Ω resistor
60
50
AMPLITUDE (dBµV/m)
40
30
20
10
0
0
200
400
600
VERTICAL POLARIZATION
PEAK DETECTOR
on OUT5 and a 13Ω resistor on OUT3. Linear Technology
has made every effort to provide useful and accurate EMI
data, but it remains the responsibility of the customer to
ensure product compliance.
CLASS 5 PEAK LIMIT
LTC3256
800
1000
DC2375A F08
FREQUENCY (MHz)
DC2375A DEMO BOARD
(WITHOUT EMI FILTER)
14V INPUT TO 5V AT 100mA
AND 3.3V AT 250mA
Figure 8. Radiated V
IN
without Filter Vertical Peak Data
60
50
AMPLITUDE (dBµV/m)
40
30
20
10
0
0
HORIZONTAL POLARIZATION
PEAK DETECTOR
CLASS 5 PEAK LIMIT
LTC3256
200
400
600
800
1000
DC2375A F09
FREQUENCY (MHz)
DC2375A DEMO BOARD
(WITHOUT EMI FILTER)
14V INPUT TO 5V AT 100mA
AND 3.3V AT 250mA
Figure 9. Radiated V
IN
without Filter Horizontal Peak Data
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