Linear Technology DEMONSTRATION CIRCUIT 470 User manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 470
HIGH EFFICIENCY TERMINATION/TRACKING POWER SUPPLY
LTC3831
DESCRIPTION
Demonstration circuit 470 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. DC470 utilizes the LTC3831, a voltage
mode synchronous buck controller. The demo circuit
provides additional footprints for paralleling more MOS-
FETs and input/output capacitors for higher current ap-
plications. The output voltage (V
OUT
) equals half of the
reference voltage (V
REF
). An external reference can be
provided to program the output voltage directly. In the
absence of the external reference, the potentiometer R11
can be used to adjust the output voltage.
SPECIFICATIONS
• V
IN
5V typical (3V–8V)
• V
OUT
V
REF
/2, preset at 1.25V by R11
• I
OUT
± 10A continuous, ± 12A
MAX
with air flow
100LFM and 5V input
SETUP NOTES
3.3V INPUT OPERATION
The demo board uses a Si7440DP, a logic level
MOSFET, to optimize for the 5V input application. If the
input voltage is 3.3V, this MOSFET is not the best op-
tion. To achieve the best performance, one of the fol-
lowing 2 options must be implemented. Otherwise, the
MOSFETs may not be properly driven and the circuit
may not produce the rated currents.
• Replace Power MOSFETs Q1 and Q3 with sub-logic
level MOSFETs such as Si7448DP
• Stuff the optional triple charge pump circuit consist-
ing of D4, D5 and C9 and depopulate R17.
EXTERNAL REFERENCE
The output of this demo board can be programmed by
the external reference at the VREF pin.
NOTE: R11 and R10 must be removed before applying
VREF.
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 power source to the VIN and
GND pins using wires capable of handling 6A current.
If required, connect the reference voltage V
REF
for the
V
OUT
to the VREF pin.
2. Turn on the 5V input power supply. Adjust R11 such
that V
REF
= 2.5V.
3. Measure V
OUT
. It should read about 1.25V ± 0.05V.
SOURCING CURRENT TEST (FIGURE 1)
4. Turn off the input power supply V
IN
first.
5. Connect the load to the VOUT and GND pins with the
positive terminal of the load connecting to VOUT.
6. Turn on V
IN
.
7. Increase the load current to 12A. If VREF is fixed at
2.5V, VOUT should read about 1.25V
± 0.05V
SINKING CURRENT TEST (FIGURE 2)
8. Turn off the input power supply V
IN
first.
9. 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.
10. Turn on V
IN
.
11. Increase the load current to 12A. If V
REF
is fixed at
2.5V, V
OUT
should read about 1.25V ± 0.05V.
1

DEMO BOARD QUICK START GUIDE 470
HIGH EFFICIENCY TERMINATION/TRACKING POWER SUPPLY
+
–
LOAD
+
–
+
–
+
–
+–
OPTIONAL
VREF
(2.5V)
IOUT
IIN
VIN (3.3V–8V)
+–
+
–
Figure 1. Proper Measurement Equipment Setup for Output Sourcing Current
+
–
+
–
+
–
+–
LOAD
+
–
OPTIONAL
V
REF
(2.5V)
I
OUT
I
IN
V
IN
(3.3V TO 8V)
+
–
+–
Figure 2. Proper Measurement Equipment Setup for Output Sinking Current
2