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ISL91108IIA-EVZ/ISL91108IIN-EVZ Evaluation Board
User Guide
Evaluation Board Features
• ISL91108 high efficiency buck-boost regulator
• Input voltage rating from 1.8V to 5.5V
• Resistor programmable output voltage on the
ISL91108IIA-EVZ evaluation board
• Fixed 3.3V output voltage on the ISL91108IIN-EVZ
evaluation board
• Up to 1.5A output current (PVIN = 3.0V, V
OUT
= 3.3V)
• 2.5MHz switching frequency
• Jumper selectable EN (enabled/disabled)
• Jumper selectable MODE (auto-PFM/forced-PWM)
• Connectors, testpoints, and jumpers for easy evaluation
Required Equipment
• Power supply capable of delivering up to 5.5V and 4A
• Electronic load
• Multimeter to measure voltages and currents
• Oscilloscope
Testpoints, Connectors, and
Jumpers
Quick Setup Guide
1. Install jumper on J3, shorting EN to VIN.
2. Install jumper on J4, shorting MODE to VIN.
3. Connect power supply to J1, with voltage setting between
1.8V and 5.5V.
4. Connect electronic load to J2.
5. Place scope probes on VOUT testpoint, and other testpoints
of interest.
6. Turn on the power supply.
7. Monitor the output voltage startup sequence on the
scope. The waveforms will look similar to that shown in
Figures 1 and 2.
8. Turn on the electronic load.
9. Measure the output voltage with the voltmeter. The voltage
should regulate within data sheet spec limits.
10. To determine efficiency, measure input and output voltages
at the Kelvin sense testpoints (S+ and S-) which are part of
J1 and J2 headers. The bench power supply can be
connected to the PVIN and GND headers on J1. The
electronic load can be connected to the VOUT and GND
headers on J2. Measure the input and output currents.
Calculate efficiency based on these measurements.
11. To test external sync, remove the jumper at J4, then apply
an external clock between 2.75MHz and 3.25MHz on the
MODE input (the center pin of header J4).
TABLE 1. DESCRIPTION OF TEST POINTS
TEST POINT(S)
DESCRIPTION
TP1
LX1 (Input side of power inductor)
TP2
LX2 (Output side of power inductor)
TP3
V
OUT
TABLE 2. DESCRIPTION OF CONNECTORS
CONNECTOR
DESCRIPTION
J1
Header for connecting input power. Includes S+ and S-
sense lines.
J2
Header for connecting external load. Includes S+ and
S- sense lines.
TABLE 3. DESCRIPTION OF JUMPERS
JUMPER
DESCRIPTION
J3
Jumper to select EN input logic state. Set EN = V
IN
to
enable device, or set EN = GND to disable device.
J4
Jumper to select MODE input logic state. Set
MODE = V
IN
to enable auto-PFM mode, or set
MODE = GND to select forced PWM mode.
To use external sync feature, remove this jumper and
apply an external clock between 2.75MHz and
3.25MHz on the center pin on the J4 header.
March 11, 2014
AN1903.1
Application Note 1903
Author: Sameer Dash
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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