User Guide 046
3
UG046.0
August 28, 2015
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What’s Inside
The evaluation board includes the following materials:
• ISL70003ASEHEV2Z evaluation board
•
ISL70003ASEH
Datasheet
• UG046, “ISL70003ASEHEV2Z Evaluation Board User Guide”
Recommended Test Equipment
• 12V power supply with at least 5A current capability
• Electronic load capable of sinking current to 7A
• Digital multimeters (DMMs)
• A 500MHz dual or quad trace oscilloscope
Quick Start
1. Set the power supply voltage to 12V. Connect the positive lead
of the power supply to VIN and the negative lead of the power
supply to GND. Turn on the power supply.
2. Connect one DMM to monitor the input voltage and another
DMM to monitor the output voltage, confirm it is 3.3V.
Evaluating ISL70003ASEH
A complete evaluation of this evaluation board is easily
accomplished and the user can easily change the operating
points by changing resistor values. Following are simple
instructions as to how to change the output voltage, the V
IN
POR
and Overcurrent Protection (OCP) thresholds to allow for a
customized evaluation.
Setting Other Output Voltages
The output voltage of the regulator is programmed via an
external resistor divider that is used to scale the output voltage
relative to the 0.6V reference voltage. The output voltage is set
for 3.3V on this circuit. To modify the output voltage, substitute
R
4
for a different value according to
Equation 1
:
Changing the V
IN
POR Voltage Threshold
After the EN input requirement is met, the ISL70003ASEH
remains in shutdown until the voltage at the POR pin rises above
its threshold. The POR circuitry prevents the controller from
attempting to soft-start before sufficient bias is present at the
PVINx pins. The rising POR Vth is set for ~10.2V on this circuit,
see
Figure 6
.
The POR threshold voltage is also programmed via an external
resistor divider. To modify the rising POR threshold voltage
(V
PORR
), substitute PORR2 for a different value according to
Equation 2:
Changing the Overcurrent Protection Level
The ISL70003ASEH features dual redundancy in the overcurrent
detection circuitry, which helps avoid false overcurrent triggering
due to single-event effects. Two external 4.02k
Ω
resistors (ROCA,
ROCB) from pins OCSETA and OCSETB to AGND set the inductor
peak current threshold at ~8.96A for the Overcurrent Protection
(OCP) trip point. See
Figure 8
for the relationship between the
peak current sensed in the IC and the DC output current. Use
Equation 3
to determine the resistor value for the desired peak
inductor overcurrent protection level.
Schematic and BOM
A schematic and BOM of the ISL70003ASEHEV2Z evaluation
board are shown on
page 6
and
page 7
, respectively. The BOM
shows components that are representative of the types needed
for a design, but these components are not space qualified.
Equivalent space qualified components would be required for
flight applications.
PCB Design
PCB design is critical to high-frequency switching regulator
performance. Careful component placement and trace routing
are necessary to reduce voltage spikes and minimize
undesirable voltage drops. Selection of a suitable thermal
interface material is also required for optimum heat dissipation
and to provide lead strain relief.
Optimize load regulation by reducing noise from the power and
digital grounds into the analog ground by splitting ground into 3
planes; analog, digital and power. Bypass or ground pins
accordingly to their design preferred ground. Independently tie
each of the analog and digital grounds to power ground via a
single trace in a low noise area.
PCB Plane Allocation
On the ISL70003ASEHEV2Z, four layers of two ounce copper is
used as recommended. Layer 2 should be a dedicated ground
plane with all critical component ground connections made with
vias to this layer. Layer 3 should be a dedicated power plane split
between the input and output power rails. Layers 1 and 4 should
be used primarily for signals, but can also provide additional
power and ground islands as required. This evaluation platform is
designed with
6A maximum of output current capability.
PCB Component Placement
Components should be placed as close as possible to the IC to
minimize stray inductance and resistance. Prioritize the
placement of bypass capacitors on the pins of the IC in the order
shown: REF, SS, AVDD, DVDD, PVINx (high-frequency capacitors),
EN, PGOOD, PVINx (bulk capacitors).
Locate the output voltage resistive divider as close as possible to
the FB pin of the IC. The top leg of the divider should connect
directly to the POL and the bottom leg of the divider should
connect directly to AGND. The junction of the resistive divider
should connect directly to the FB pin.
R
4
k
15
V
OUT
0.6V
–
-------------------------------------------
=
(EQ. 1)
PORR2
100k
V
PORR
1.2V
–
0.6
-------------------------------------------------
1
–
=
(EQ. 2)
ROC(A/B) (
Ω
)
36024
I
OCP
A
-----------------------------
=
(EQ. 3)
