Application Note 1946
5
AN1946.0
July 7, 2014
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Quick Start Guide
Setup of Test Equipment
• Prepare 2 Power Supplies, 1 Electric Load, 4 Digital
Multimeters (DMM) and 1 Oscilloscope.
- The first power supply (VIN Power Supply) will be used for
the VIN power rail and should have the capability to supply
up to 60V/5A.
- The second power supply (EN Power Supply) will be used to
supply bias for EN and should have the capability to supply
5V/0.5A. This power supply is not necessary if EN is
connected to VIN with J28 and J10.
- The Electric Load (or Resistive Load) will be used as the load
for V
OUT
and should have a capability to sink up to 20A.
- The DMMs will be used to monitor the output voltage, the
output current, the input voltage and the input current.
• External Connections
- Connect the VIN Power Supply between VIN(J1) and GND(J2).
- Connect the EN Power Supply (if used) between EN and GND
(J28-center and GND side).
- Connect the Electric Load between VOUT(J26) and GND(J27).
- Place the DMMs appropriately where the parameters are to
be measured. The input and output voltage can be measured
using J4 and J24. The input and output current should be
monitored in series with the respective positive terminals of
VIN and VOUT.
NOTE: To measure the voltage of high current nodes, it is recommended to
use Kelvin connection to avoid the effect of parasitic resistances of the
connections. These connections are supplied at J4 and J24.
• Recommended Power Supply and Load set up
- Set the EN Power Supply voltage to 3.3V. At this time, the
power supply output should remain off.
- Set the VIN Power Supply voltage to 36V (15V~55V). At this
time, the power supply output should remain off.
- Set the Electric Load to 0A. At this time, the load should
remain off.
Measurement Setup
On the ISL78268 Evaluation Board, user can select the following
operation modes; fault response (Hiccup or Latch-off), switching
mode (Diode Emulation mode or Forced PWM mode) and
Average Current Limit (ACL) by changing the connection of the
HIC/LATCH and IMON/DE jumper pins.
Table 2 on page 6
shows
the detailed jumper pin settings for different operation modes.
Three typical operation modes examples are shown as follows:
1. Diode Emulation Mode Enabled/Hiccup Mode Enabled/ACL
disabled
• Short a jumper between HIC/LATCH and VCC at J13 to set
to Hiccup Mode
• Short a jumper between IMON/DE and GND at J8 to
disable the Average Current Limit
• Ensure the jumper between IMON/DE and VCC at J11 is
removed (open) to operate in DE Mode
1.1. Power-up and Initial Confirmation
• Turn on the output of VIN Power Supply. Keep EN
Power Supply output off.
- Keep the Electric Load off
- Confirm the voltage applied to VIN of the evaluation
board is correct.
- Confirm the supply current of VIN Power Supply is
less than 3µA.
- Sweep VIN from 15V to 55V
• Confirm the supply current of VIN Power supply is
less than 10µA at all input voltages.
- Set VIN Power Supply to 36V (or desired voltage)
and enable the output of the EN Power Supply.
• Keep the electric load off.
• Confirm the evaluation board output voltage is 12V.
• Confirm the PVCC voltage is 5.2V.
• Confirm the supply current of VIN Power Supply is
approximately 5mA.
• Confirm the frequency of the output clock from
CLKOUT (J19) is approximately 300kHz and the
pulse width is approximately 270ns.
• Confirm the pulse skipping switching at PHASE
node (J20).
J22
ISEN2P - GND
Test point to monitor ISEN2P waveform (Do Not short with jumper). For accurate monitoring of the voltage
difference between ISEN2P and ISEN2N, place a differential probe between Pin 2 of J22 and Pin 2 of J23.
J23
ISEN2N - GND
Test point to monitor ISEN2N waveform (Do Not short with jumper). For accurate monitoring of the voltage
difference between ISEN2P and ISEN2N, place a differential probe between Pin 2 of J22 and Pin 2 of J23.
J24
VOUT - GND
Test point to monitor the output voltage (VOUT) (Do Not short with jumper).
J26
VOUT
Positive terminal of buck regulator output (Do Not short with jumper).
J27
GND
Negative terminal of buck regulator output. (ground).
J28
EN - VIN
To enable the system automatically when VIN is applied, short J28 with a jumper and also short between Pin 2 and
Pin 3 of J10.
TABLE 1. ISL78268EV1ZB CONNECTOR/MONITOR-PIN DESCRIPTION (Continued)
CONNECTOR/
TERMINAL
SIGNAL NAME
DESCRIPTIONS
