DC524A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 524
POSITIVE INPUT TO NEGATIVE OUTPUT DC/DC CONVERTER
LTC3704
DESCRIPTION
Demonstration circuit 524 is a positive input to negative
output converter featuring the LTC3704 switching controller. The DC524 converts a 5V–15V input to a –5.2V
output and provides up to 2.5A of output current from
5V input. The converter operates at 300kHz with a high
efficiency of 89%. The DC524 is set to operate in No
RSENSE™ mode with input voltages up to 15V. However,
DC524 can be modified for higher input voltages with an
optional current sense resistor. The circuit features optional soft-start circuitry that can be enabled or disabled
with a single jumper. Also, DC524 has a jumper to program either continuous or Burst Mode™ operation. The
DC524 can be synchronized to an external clock of up to
400kHz. Please refer to LTC3704 data sheet for design
details and applications information.
The DC524 can produce up to 3A from a 5V input
source, 4A from 10V source and 5A from 15V source.
The actual current capability also depends on the operating temperature and available airflow. As MOSFET Q1
gets hot, its RDS(ON) increases and the available output
current decreases.
Design files for this circuit board are available. Call
the LTC factory.
Burst Mode is a registered trademark and No RSENSE is a trademark of Linear Technology Corporation
Table 1. Performance Summary
PARAMETER
CONDITION
VALUE
Minimum Input Voltage
4.5V
Maximum Input Voltage
No RSENSE mode
18V (or higher with some modifications)
VOUT
VIN = 5V to 15V, IOUT1 = 0A to 2.5A
–5.2V ±3%
Typical Output Ripple VOUT
VIN = 5V to 15V, IOUT1 = 0A to 2.5
50mVP–P
Nominal Switching Frequency
300kHz
QUICK START PROCEDURE
Demonstration circuit 524 is easy to set up to evaluate
the performance of the LTC3704. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:
NOTE: When measuring the input or output voltage rip-
ple, 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. See Figure 2 for
proper scope probe technique.
1. Place jumper JP1 in the ENABLE position.
2. With power off, connect the input power supply to Vin
and GND. Make sure that the input power supply has
sufficient current rating at minimum input voltage for
the required output load.
3. Turn on the power at the input.
NOTE: Make sure that the input voltage does not ex-
ceed 15V.
4. Check for the proper output voltage: Vout = –5.2V
NOTE: If there is no output, temporarily disconnect the
load to make sure that the load is not set too high.
5. Once the proper output voltage is established, adjust
the load within the operating range and observe the
output voltage regulation, ripple voltage, efficiency
and other parameters.
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 524
POSITIVE INPUT TO NEGATIVE OUTPUT DC/DC CONVERTER
–
+
+
+
–
–
+
–
OPTIONAL
EXTERNAL
CLOCK
SEE "EXTERNAL
CLOCK CONNECTION"
SECTION
+
+
LOAD
–
–
–
GND
Figure 1. Proper Measurement Equipment Setup
VIN
+
Figure 2. Scope Probe Placement for
Measuring Input or Output Ripple
CONNECTING AN EXTERNAL CLOCK
3. Remove resistor R6.
1. Turn the input power source Off.
4. Install 0Ω resistor R7.
2. Remove the Burst Mode jumper.
3. Set the clock source pulse amplitude to 5V and set
the frequency between 330 kHz and 400kHz.
4. Turn the clock source off.
5. Connect the clock source (pulse generator with TTL
output) to the middle pin of Burst Mode jumper.
6. Apply input power and observe the switching fre-
quency of 300kHz.
7. Turn the clock source on and observe the switching
frequency go up to the switching frequency of the external clock.
USING AN OPTIONAL CURRENT SENSE RESISTOR
MONITORING THE MOSFET CURRENT
Monitor the MOSFET current through the Rs1 resistor.
1. Connect a 50Ω coaxial cable across Rs1 with the
shield connected to the ground connection of Rs1.
2. Use a 50Ω surface mount resistor to connect the cen-
ter conductor of the coaxial cable to the Rs1 terminal
which is connected to the source of MOSFET Q1.
3. Set the scope input to 50Ω and connect the coaxial
cable to the scope.
4. Set the scope to 5mV/division or less. The current
scale with 1mΩ Rs1 and 5mV/div is 10A/div (50Ω resistor at the input of coaxial cable forms 2:1 divider
with 50Ω input impedance of scope).
1. Refer to LTC3704 data sheet to determine the proper
resistor value.
2. Replace current sense resistor Rs1 with the correct
value.
2
5
4
3
2
1
1
2
C
1
RUN
2
ITH
VIN 9
3
NFB
INTVCC 8
4
FREQ
5
MODE/SYNC
4
D
3
D
SENSE 10
GATE 7
C
GND 6
B
B
A
A
5
4
3
2
1
Bill Of Material
Demo Bd. #524A
Linear Technology Corporation
LTC3704EMS
6/17/2005
Item
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Qty Reference
1
1
1
1
3
1
1
1
1
1
1
2
2
1
1
1
1
1
1
1
1
1
2
1
1
1
0
6
1
4
4
1
2
CC1
CC2
CDC
CIN1
CO1,CO2,CO3
CO4
CSS1
CV1
C1
D1
D2
JP1,JP2
XJP1,XJP2
L1
Q1
Q2
RC1
RSS1
RSS2
RS1
RT1
R1
R6,R2
R3
R4
R5
R7
(OPT)
TP1-TP6
U1
Part Description
CAP., X7R 2200pF 50V 10%
CAP., NPO, 100PF, 50V, 10%
CAP., X7R 22uF 25V 20%
CAP., X5R 47uF 16V 20%
CAP., X5R 100uF 6.3V 20%
CAP., X5R 47uF 6.3V 20%
CAP., X7R, 0.1UF, 16V, 10%
CAP., Y5V 4.7uF 10V 80%
CAP., X7R 0.1uF 25V 10%
Schottky Rect., 40V/8Amp
Schottky Diode, Super-Mini
Headers, 3 Pins 2mm Ctrs.
Shunt, 2 Pins 2mm Ctrs.
Dual Inductor, QTR-Pak
Mosfet N-Chan., PowerPAK SO-8
XSTR, NPN Small Sig.
RES., Chip 20K 0.1W 1%
RES., Chip 1K 0.1W 5%
RES., Chip 100 Ohms 0.1W 5%
RES., Chip 0.001 1W 5%
RES., Chip 80.6K 0.1W 1%
RES., Chip 274K 0.1W 1%
Jumper, Chip 0 0.1W 5%
RES., CHIP, 1.24K, 0.1W, 1%
RES., CHIP, 4.02K, 0.1W, 1%
RES., Chip 133K 0.1W 1%
Jumper, Chip O 0.1W 5%
Turret, Testpoint
I.C., NoRsense DC/DC Controller
SCREW, #4-40, 1/4"
STANDOFF, #4-40 1/2"
PRINTED CIRCUIT BOARD
STENCIL
Page 1 - of - 1
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ANY
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DEMO CIRCUIT 524A
STENCIL 524A
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