Linear Technology DEMONSTRATION CIRCUIT 470 Quick Start Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 470

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
reference voltage (V ). An external reference can be
REF
provided to program the output voltage directly. In the

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

QUICK START PROCEDURE

Refer to Figure 1 and Figure 2 for proper measurement
equipment setup and follow the procedure below:
Connect the input 5V power source to the VIN and
1.
GND pins using wires capable of handling 6A current.
If required, connect the reference voltage V
V to the VREF pin.
OUT
Turn on the 5V input power supply. Adjust R11 such
2.
that V = 2.5V.
REF
. It should read about 1.25V ±0.05V.
Measure V
3.
OUT

SOURCING CURRENT TEST (FIGURE 1)

Turn off the input power supply V
4.
Connect the load to the VOUT and GND pins with the
5.
positive terminal of the load connecting to VOUT.
HIGH EFFICIENCY TERMINATION/TRACKING POWER SUPPLY
) equals half of the
OUT
for the
REF
first.
IN
absence of the external reference, the potentiometer R11
can be used to adjust the output voltage.

SPECIFICATIONS

• V
5V typical (3V–8V)
IN
• V
V /2, preset at 1.25V by R11
OUT REF
• I ±10A continuous, ±12A
OUT
100LFM and 5V input
• 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.
R11 and R10 must be removed before applying
NOTE:
VREF.
Turn on V .
6.
IN
Increase the load current to 12A. If VREF is fixed at
7.
2.5V, VOUT should read about 1.25V±0.05V

SINKING CURRENT TEST (FIGURE 2)

Turn off the input power supply V
8.
Connect the load to the VIN and VOUT pins with the
9.
positive terminal of the load connecting to VIN and
the negative terminal of load connecting to VOUT.
Turn on V .
10.
IN
Increase the load current to 12A. If V
11.
should read about 1.25V ±0.05V.
2.5V, V
OUT
LTC3831
with air flow
MAX
first.
IN
is fixed at
REF
1