1
®
AN1459.0
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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ISL8107EVAL2Z
Introduction
The ISL8107 is a single-phase PWM controller that operates
from 9V to 75V bias supply voltage. The PWM controller
drives an external high-side N-Channel MOSFET in a
non-synchronous buck converter topology. The ISL8107
features input voltage feed-forward compensation and
overcurrent protection, etc. For a more detailed description
of the ISL8107 functionality, refer to the ISL8107 Data Sheet
http://www.intersil.com/data/fn/fn6605.pdf.
The ISL8107EVAL2Z Reference Design
The ISL8107EVAL2Z evaluation board is designed to meet
the output voltage and current specifications shown in
Table 1. Schematic, bill of materials, and layout plots are
included.
Quick Start Evaluation
Figure 1 shows a photograph of the ISL8107EVAL2Z board.
Circuit Setup
The input supply of the power stage can be connected to the
terminals P5 (V
IN
) and P6 (PGND). For single supply
application, the ISL8107’s bias supply can be tied to V
IN
through J1 with shunt between pins 2 and 3. When using
separate supplies, provide the ISL8107 bias voltage through
P1 (VBIAS) with J1’s shunt between pins 1 and 2. The load
can be connected to terminal P7 (VOUT) and P8 (PGND).
TP3 and TP4 can be used for DMM to measure the output
voltage. Enabling and disabling the controller can be done
through the toggle switch, SW1.
ISL8107EVAL2Z Performance
Start-Up
Figure 2 shows the start-up waveforms of the
ISL8107EVAL2Z. Upon the VCC and VFF exceeding their
rising POR thresholds, the ISL8107 provides initially 2µA to
charge the soft-start capacitor, C
SS
, connected to the ENSS
pin. If the voltage at this pin is allowed to rise (the toggle
switch, SW1, at ON position), the voltage on ENSS pin will
ramp-up with at a slope determined by the 2µA current and
the value of the soft-start capacitor. When the voltage at
ENSS reaches 0.77V, the oscillator circuit is active, and
generates sawtooth waveform. At the same time, the
soft-start current is increased to 33µA; the ENSS voltage
then ramps up at a faster rate. The UGATE starts switching
when the ENSS voltage reaches 1.4V (Typ).
TABLE 1. ISL8107EVAL2Z DESIGN PARAMETERS
PARAMETER
MIN
TYP
MAX
Input Voltage (V
IN
)
18V
48V
75V
Output Voltage (V
OUT
)
12V
Output Voltage Ripple
30mV
Continuous Load Current
5A
Switching Frequency
200kHz
FIGURE 1. ISL8107EVAL2Z
FIGURE 2. START-UP WAVEFORMS
V
OUT
ENSS
PHASE
PGOOD
Application Note
June 9, 2009
