Application Note 1181
3
AN1181.1
November 28, 2011
Figures 5 and 6 show the PHASE1 signal (which has the same
timing as UGATE1) and the output voltage ripple on VOUT1 at no
load and 3A load. The switching frequency is 1.4 MHz.
Figure 7 shows the overcurrent hiccup mode already in
operation. At time T0, the SS/EN2 is discharged to GND (it may
not have time to reach GND, due to the limited size of the
discharge transistor, plus the size of the timing capacitor). Once
SS/EN2 is below ~1V, the output should shut off, and the load
current goes to zero; this occurs by time T1. Once SS/EN2 rises
above 1V again, the VOUT2 will try to turn on again. If the output
remains shorted, the output current will be limited on each clock
cycle to an average value low enough to keep the dissipation
reasonable.
Conclusion
The ISL6442EVAL1Z evaluation board showcases a simple, but
high-performance dual regulator, providing control in a variety of
applications, with emphasis on computer systems. The
high-current MOSFET drivers of the ISL6442 yield a highly
efficient power conversion solution with a reduced number of
external components in a compact footprint.
Documentation
See the following pages for more detailed information, including:
• “Schematic” of ISL6442EVAL1Z
• Table 1, “BILL OF MATERIALS” on page 5
• “ISL6442EVAL1Z Board Layout” on page 7. Note that this
board layout has not been fully optimized for performance or
minimum board area, primarily due to the various options, test
points, and other features to make testing easier. So while it
follows most of the recommended practices, it could
potentially be improved for any given single application.
References
Datasheet:
ISL6442 datasheet
Visit us on the internet, at:
http://www.intersil.com
CH1
PHASE1
CH2 (AC)
VOUT1
(20mV/DIV)
FIGURE 5. PWM1 SWITCHING AND RIPPLE WAVEFORMS AT
NO LOAD
(2V/DIV)
0.2µs/DIV; VOUT1 = 1.8V; VIN = 6V
CH1
PHASE1
CH2 (AC)
VOUT1
(20mV/DIV)
FIGURE 6. PWM1 SWITCHING AND RIPPLE WAVEFORMS
AT 3A LOAD
(2V/DIV)
0.2µs/DIV; VOUT1 = 1.8V; VIN = 6V
FIGURE 7. PWM2 OVERCURRENT HICCUP MODE
CH1
SS/EN2
CH4
I
LOAD2
CH2
VOUT2
(1V/DIV)
2ms/DIV; VOUT2 = 3.3V; VIN = 6V; ROCSET = 2.15kW
(5A/DIV)
(2V/DIV)
T0
T1
