ISL6567 Intersil Corporation, ISL6567 Datasheet - Page 12

• Manufacturer Part Number: ISL6567
• Description: Multipurpose Two-Phase Buck PWM Controller
• Manufacturer: Intersil Corporation

OVERCURRENT PROTECTION
The individual channel currents, as sensed via the PHASE
pins and scaled via the ISEN resistors, as well as their
combined average are continuously monitored and
compared with an internal overcurrent (OC) reference. If the
combined channel current average exceeds the reference
current, the overcurrent comparator triggers an overcurrent
event. Similarly, an OC event is also triggered if either
channel’s current exceeds the OC reference for 7
consecutive switching cycles.
As a result of an OC event, output drives turn off both upper
and lower MOSFETs, and the SS capacitor is discharged via
a 20μA current source. The behavior following this standard
response varies depending whether the controller is
operating in internal (using internal reference; MON > 3.5V)
or external reference mode (using external reference; MON
< 3.5V). As shown in Figure 6, the soft-start capacitor
discharge prompted by the OC event is followed by two SS
cycles, during which the ISL6567 stays off. Following the
dormant SS cycles, the controller attempts to re-establish
the output. Should the OC condition been removed, the
output voltage is ramped up and operation resumes as
normal. Should the OC condition still be present and result in
another OC event, the entire behavior repeats until the OC
condition is removed or the IC is disabled. Figure 7 details
the OC behavior while in external reference mode. Following
the OC event, the output drives are turned off, the ISL6567
latches off, and the SS capacitor is discharged to ground.
Resetting the OC latch involves removal of bias power or
cycling of the EN pin (pictured in Figure 7). Should the OC
event been removed, the controller initiates a new SS cycle
and restores the output voltage.
GND>
GND>
GND>
GND>
FIGURE 6. OVERCURRENT BEHAVIOR WHILE IN INTERNAL
OUTPUT CURRENT
REFERENCE MODE
12
OUTPUT VOLTAGE
EN
SS
ISL6567
ISL6567
SETTING THE OUTPUT VOLTAGE
The ISL6567 uses a precision internal reference voltage to
set the output voltage. Based on this internal reference, the
output voltage can thus be set from 0.6V up to a level deter-
mined by the input voltage, the maximum duty cycle, and the
conversion efficiency of the circuit; the following equation
estimates this maximum amplitude the output voltage can be
regulated to. Obviously, insure that the input voltage and all
the voltages sampled by the ISL6567 do not exceed the con-
troller’s absolute maximum limits, or any other limits specified
in this document.
V
GND>
GND>
GND>
GND>
OUTMAX
FIGURE 8. SETTING THE OUTPUT VOLTAGE AT THE INPUT
FIGURE 7. OVERCURRENT BEHAVIOR WHILE IN EXTERNAL
DIFFERENTIAL
AMPLIFIER
AMPLIFIER
ERROR
V
OUTPUT CURRENT
=
REF
SS
d
OF THE DIFFERENTIAL AMPLIFIER
REFERENCE MODE
MAX
X1
+
-
⋅
V
ISL6567
IN
+
-
⋅
Efficiency
VDIFF
RGND
FB
EXTERNAL CIRCUIT
VSEN
OUTPUT VOLTAGE
EN
R
1
R
P
R
S
March 20, 2007
To V
+
FN9243.2
-
OUT