Lattice Semiconductor L-ASC10 User Manual Download Page 14

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ASC Breakout Board

Overview of Trim and Margin

The board provides footprints for four DC-DC modules. Since all four are similarly designed and laid out, this sec-
tion will provide an overview of the DC-DC circuit rather than provide a separate section for each DC-DC. Foot-
prints are provided for both 5-pin SIP modules and DOSA power converters. The circuits shown in the schematic
appendix support the NQR002A0X4 SIP from GE Industrial and the OKY-T/3-D12 DOSA converter from Murata.
None of the components associated with the DC-DC operation (shown in Table 4) are populated on the breakout
board.

The ASC Breakout board provides footprints and circuit connections for five trimming resistors for each DC-DC.
These five resistors are shared by both the SIP and DOSA footprints because only one supply can be populated at
a time. The resistors are organized in an “H” pattern both in the schematic and on the board layout. The resistors
are named in the schematic to match the names used in the Platform Designer Trim-view calculator. The names
are listed and described in Table 5 below. Typically only three resistors are suggested by the calculator; a pull-up, a
pull-down, and a series resistor. The exact population of the “H” pattern depends on many factors that the calcula-
tor takes into account such as type of DC-DC, output voltage, and range of trim. The ASC Breakout board provides
pads and connections to support any result from the Trim Calculator. However, with certain supplies and option set-
tings, the calculator can produce a result that only uses two resistors: a pull-down and series resistor. The DC-DCs
on the ASC Breakout board are populated with the two resistor solution. A key requirement for the calculator to pro-
duce a two-resistor solution is the Bi-Polar Zero (BPZ) voltage of the Trim Cell has to match the DC-DC internal ref-
erence voltage. Otherwise the calculator will add a pull-up or pull-down resistor in attempt to offset the imbalance
between the BPZ voltage setting and DC-DC reference voltage. The values shown in the schematic have been cal-
culated for the NQR002A0X4 SIP from GE Industrial. For more information on the Trim interface and Calculator
please see AN6074,

Interfacing the Trim Output of Power Manager II Devices to DC-DC Converters

and the

Plat-

form Designer 3.1 User Guide

Table 5. Trim Resistor "H-Network" Names.

In order for the CLT circuits within the ASC to operate properly the output of the supply needs to be monitored by
the correct VMON input. The ASC Breakout board illustrates the correct connections by using TRIM1 with VMON1
for DCDC1, TRIM2 with VMON2 for DCDC2, all the way to TRIM4 with VMON4 for DCDC4. As discussed in the
Voltage Monitor Operation section, the DC-DC outputs are connected to the VMON inputs using a series resistor
with a value of 270

Ω

. The series resistor is not required in customer designs; its only function on the breakout

board is to isolate the DC-DC outputs from the VMON test point. The VMON series resistor allows another voltage

LED5

2, 4

DCDC4 control signal from GPIO5. Safe state is low.

OUT_DCDC1

2, 3

DCDC1 Output connected to VMON1 via R23.

OUT_DCDC2

2, 3

DCDC2 Output connected to VMON2 via R32.