DC2851A User Guide
LT7200S
Quad 18V, ±5A
Synchronous Monolithic
Step-Down Regulator
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Quick Start Procedure
The evaluation kit DC2851A is easy to set up to evaluate
the performance of the LT7200S. See Figure 1 for proper
measurement equipment setup and follow this procedure.
1. With power off, place the jumpers in the following
positions:
JP1
JP2
JP3
JP4
JP5
JP6
RUN1 RUN2 RUN3 RUN4
MODE/
SYNC
PHMODE
ON
ON
ON
ON
FCM
LOW
2. With power off, connect the input power supply to
VEMI+ and VEMI-.
3. With power off, connect the loads from VOUT1,
VOUT2, VOUT3, and VOUT4 to GND.
4. Place the voltmeters across the output terminals to get
accurate output voltage measurements.
5. Turn on the power at the input.
NOTE: Make sure that the input voltage does not exceed
18V and VIN > VOUT.
6. Check for proper output voltages. Regulate the output
at 1.2V (±4%), 1.8V (±4%), 3.3V (±4%), and 5.0V (±4%).
NOTE: If there is no output, temporarily disconnect the
load to make sure the load is not set too high.
7. Once the proper output voltage is established, adjust
the load within the operating ranges and observe the
output voltage regulation, ripple voltage, efficiency, and
other parameters.
NOTE: When measuring the input or output voltage
ripple, take care to avoid a long ground lead on the
oscilloscope probe. Measure the output voltage ripple by
touching the probe tip directly across the output capacitor.
See Figure 2 for the proper scope technique.
8. Add an external clock to the SYNC terminal when SYNC
function is used (JP5 on the CLKIN position). Make sure t
choose the R50 resistor to set the LT7200S switching
frequency close to the synchronization frequency.
9. (Option) 4-Phase 20A Output Circuit Configuration:
DC2851A can be configured as a 4-Phase 20A output
regulator.
The following simple modifications are required:
1. Tie VIN1, VIN2, VIN3, and VIN4 together with 0Ω
resistors (R29, R30, R31).
2. Tie RUN1, RUN2, RUN3, and RUN4 together with 0Ω
resistors (R33, R34, R48).
3. Tie TRACK1, TRACK2, TRACK3, and TRACK4
together with 0Ω resistors (R58, R59, R60).
4. Tie FB1, FB2, FB3, and FB4 together with 0Ω resistors
(R55, R56, and R57). Keep the resistor divider network on
one of the 4 channels to program the desired output
voltage and remove the resistor divider networks of other
3 channels.
5. Tie ITH1, ITH2, ITH3, and ITH4 together with 0Ω
resistors (R62, R63, R64).
6. Tie 4 channel outputs together at the exposed copper
strips on the top of the board. Connect the load from VOUT
to GND.
7. Calculate and insert the inductors needed for L1, L2, L3,
and L4 (L1=L2=L3=L4).
8. Place the PHMODE jumper (JP6) to LOW.
9. Place RUN1, RUN2, RUN3, and RUN4 jumpers to ON.
