2
dc1839af
DEMO MANUAL DC1839A
QUICK START PROCEDURE
The DC1839A is easy to set up to evaluate the performance
of the LTC3634. For a proper measurement equipment
configuration, set up the circuit according to the diagram
in Figure 1.
NOTE: When measuring the input or output voltage 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 V
IN
or V
OUT
and GND terminals. See the proper scope probe
technique in Figure 2.
Please follow the procedure outlined below for proper
operation.
1. Connect the input power supply to the V
IN
and GND
terminals. Connect the loads between the V
OUT
and GND
terminals. Refer to Figure 1 for the proper measurement
equipment setup.
Before proceeding to operation, insert jumper shunts
XJP1 and XJP2 into the OFF positions of headers JP1
and JP2, shunt XJP3 into the forced continuous mode
(FCM) position of MODE header JP3, shunt XJP4 into
the 180° (out-of-phase) position of PHASE header JP4,
shunt XJP5 into the soft-start positions of TRACK/SS
header JP5, and shunt XJP6 into the V
OUT1
voltage
options of choice of header JP6: 1.2V, 1.5V, or 1.8V.
2. Apply 5V at V
IN
. Measure both V
OUT
s; they should read
0V. If desired, one can measure the shutdown supply
current at this point. The supply current should be less
than 30μA in shutdown.
3. Turn on V
OUT1
, V
DDQ
, and V
OUT2
, V
TT
, by shifting shunts
XJP1 and XJP2 from the OFF positions to the ON posi-
tions. Both output voltages should be within a tolerance
of ±1%.
4. Vary the input voltage from 3.6V to 15V, the channel 1
load current from 0 to 3A, and the channel 2 load cur-
rent from 0 to ±3A (The V
TT
channel sinks as well as
sources current. An easy way to test this capability is
shown in the test set-up diagram; connect a variable
resistor from V
IN
to V
OUT
, along with an ampmeter. The
current will be V
IN
minus V
OUT
divided by the variable
resistor value). V
DDQ
output voltage tolerance should
be within ±2%, whereas the output voltage tolerance
of V
TT
should be within ±3%.
5. Set the load current of both outputs to 3A and the input
voltage to 12V, then measure each output ripple voltage
(refer to Figure 2 for proper measurement technique);
they should each measure less than 20mVAC. Also,
observe the voltage waveform at either switch node
(pins 16 and 17 for channel 1, and 23 and 24 for chan-
nel 2) of each regulator. (Both switch node waveforms
should be rectangular in shape and 180°out-of-phase
with each other). The switching frequencies should be
between 800kHz and 1.2MHz (T = 1.25μs and 0.833μs).
6. With the board under proper operation, observe the load
regulation, efficiency, in-phase operation (by changing
jumper XJP4 to the 90° position), or Burst Mode op-
eration (by changing jumper XJP3 to the Burst Mode
position).
7. (Optional) Moving the zero ohm resistor at RV
DDQ
,
inserting it into R
DDQIN
, and applying a voltage to turret
V
DDQIN
allows channel 2 output voltage (VTTR) to be
adjusted to any desired voltage (to one-half the voltage
at VDDQIN).
When finished, insert shunts XJP1 and XJP2 to the OFF
position(s) and disconnect the power.
Warning: If the power for the demo board is carried in
long leads, the input voltage at the part could ring, which
could affect the operation of the circuit or even exceed
the maximum voltage rating of the IC. To eliminate the
ringing, a small Poscap capacitor (for instance, AVX part
number TPSY226M035R0200) is inserted on the pads
between the input power and return terminals on the bot-
tom of the demo board. The (greater) ESR of the Poscap
will dampen the (possible) ringing voltage due to the use
of long input leads. On a normal, typical PCB, with short
traces, this capacitor is not needed.
