ISL9440AEVAL1Z datasheet(3/11 Pages) INTERSIL

3 / 11 page

AN1551.0

March 5, 2010

Load Transient Circuit Set-Up

1. Select a SOIC8 N-Channel MOSFET with VDS

breakdown >20V.

2. Install the load transient circuit as indicated on the

schematic. Refer to Figure 4 for detail.

3. R27, R22 and R25 are 10kΩ resistors for discharging

the MOSFET gates.

4. R26, R23 and R24 are current sensing resistors to

monitor the load step. For accurate measurement,

please use 5% tolerance sensing resistor or better.

To alleviate thermal stress, use 0.1Ω or smaller

resistance. The resistance of the sensing resistors

sets the current scale on the oscilloscope.

5. Apply pulse square waveform across R27, R22 or

R25. The duty cycle of the pulse waveform should be

small (<5%) to limit thermal stress on current

sensing resistor and the MOSFETs (M8, M6 or M7).

6. The amplitude of the clock sets the current step

amplitude. Adjust the clock amplitude and slew rate

to set the current step and slew rate.

7. Monitor overshoot and undershoot at corresponding

output.

FIGURE 2. PROPER TEST SET-UP

FIGURE 3. PROPER PROBE SET-UP TO MEASURE

OUTPUT RIPPLE AND PHASE NODE

RINGING

OUTPUT CAP

OR MOSFET

OUTPUT CAP

OR MOSFET

OUTPUT CAP

OR MOSFET

Application Note 1551

ISL9440AEVAL1Z Datasheet(PDF) 3 Page - Intersil Corporation