QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 518
SLIC POSITIVE INPUT TO NEGATIVE OUTPUT DC/DC CONVERTER
1
LTC3704
DESCRIPTION
Demonstration circuit 518 is a positive input to
negative output SLIC (Subscriber Line Interface
Circuit) converter featuring the LTC3704 switch-
ing controller. DC518 converts 4.5V to 15V input
to –24V and –70V output and provides over
200mA of output current from a 5V input. The
converter operates at 200kHz with high efficiency
of up to 92%. The DC518 is set to operate with
current sense resistor RS1 and input voltages up
to 15V. However, DC518 can be modified for No-
Rsense
TM
operation with a 5V input voltage, pro-
vided that MOSFET drain voltage does not exceed
36V (main output set between 0V and -24V). The
circuit features an optional soft-start circuit that can
be enabled or disabled with a single jumper.
DC518 has a jumper to program either continuous
or Burst-Mode operation and can be synchronized
to an external clock of up to 400kHz. Please refer
to the LTC3704 data sheet for design details and
applications information.
The DC518 can produce up to 200mA at both out-
puts from a 5V input source.
Design files for this circuit board are available.
Call the LTC factory.
Table 1.
Performance Summary
PARAMETER CONDITION
VALUE
Minimum Input Voltage
4.5V
Maximum Input Voltage
15V
V
OUT1
V
IN
= 5V to 15V, I
OUT1
= 0A to 0.2A
-24V ±3%
V
OUT2
V
IN
= 5V to 15V, I
OUT2
= 0A to 0.2A
-70V ±10%
Typical Output Ripple V
OUT1
V
IN
= 5V to 15V, I
OUT1
= 0A to 0.2A
200mV
P–P
Typical Output Ripple V
OUT2
V
IN
= 5V to 15V, I
OUT2
= 0A to 0.2A
500mV
P–P
Nominal Switching Frequency
200kHz
QUICK START PROCEDURE
Demonstration circuit 518 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 volt-
age 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. See Figure 2 for proper scope probe
technique.
1.
Place jumper JP1 in the Vin position. The “Pre
Reg” position is an optional bias source for appli-
cations modified for Vin higher than 36V. A bias
circuit including Q4 and D5 is installed on the
board in order to facilitate modifications for higher
Vin.
2.
With power off, connect the input power supply to
Vin and GND. Make sure that the input power sup-
ply has sufficient current rating at minimum input
voltage for the required output load.
3.
Turn on the power at the input.
