QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 450
DDR, HSTL, STTL TERMINATION POWER SUPPLY
LTC3717
DESCRIPTION
Demonstration circuit 450 is a termination power supply
that sinks or sources up to 12A current. Typical applica-
tions include termination power supplies for DDR or
QDR memories. DC450 utilizes the LTC3717, a Constant
On-Time, Valley Current Mode synchronous buck con-
troller. The demo circuit provides additional footprints
for paralleling more MOSFETs and input/output capaci-
tors for higher current applications. The output voltage
(V
OUT
) equals half of the reference voltage (V
REF
). The
default reference voltage is the input voltage, V
IN
. An
external reference can be provided to program the out-
put voltage directly.
SPECIFICATIONS
•
V
IN
5V–20V
•
V
OUT
V
REF
/2, preset at 1.25V
•
I
OUT
±
10A continuous,
±
12A
MAX
with air flow
100LFM
SETUP NOTES
JUMPER SETTINGS
JP1: shunt at
ADJ.
position
EXTERNAL REFERENCE
The output of this demo board can be programmed by
the external reference at the VREF pin.
NOTE:
R11 and R12 must be removed before applying
V
REF
.
APPLY 5V TO EXTVCC:
LTC3717 has an internal 5V LDO that provides the gate
drive for power MOSFETs. When an external 5V source
is available, apply this 5V to EXTVCC pin to disable the
internal LDO. This will improve efficiency for high V
IN
applications.
QUICK START PROCEDURE
Refer to Figure 1 and Figure 2 for proper measurement
equipment setup and follow the procedure below:
1.
Connect the input 5V–20V power source to the VIN
and GND pins using wires capable of handling 4A cur-
rent.
2.
Turn on the input power supply.
3.
Adjust R12 such that V
REF
= 2.5V (the default refer-
ence voltage).
4.
Measure V
OUT
. It should read about 1.25V
±
0.05V.
SOURCING CURRENT TEST (FIGURE 1)
5.
Turn off the input power supply VIN first.
6.
Connect the load to the VOUT and GND pins with the
positive terminal of the load connecting to VOUT.
7.
Turn on VIN.
8.
Increase the load current to 10A. V
OUT
should always
equal V
REF
/2
±
0.05V. If V
REF
is fixed at 2.5V, V
OUT
should read about 1.25V
±
0.05V.
SINKING CURRENT TEST (FIGURE 2)
9.
Turn off the input power supply VIN first.
10.
Connect the load to the VIN and VOUT pins with the
positive terminal of the load connecting to VIN and
the negative terminal of load connecting to VOUT.
11.
Turn on VIN.
12.
Increase the load current to 10A. If VREF is fixed at
2.5V, VOUT should read about 1.25V
±
0.05V.
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