isl6307b Intersil Corporation, isl6307b Datasheet - Page 23

• Manufacturer Part Number: isl6307b
• Description: 6-phase Vr11 Pwm Controller With 8-bit Vid Code Capable Of Precision Rds On Or Dcr Differential Current Sensing For Applications In Which Supply Voltage Is Higher Than 5v
• Manufacturer: Intersil Corporation

Once an overvoltage condition is detected, normal PWM
operation ceases until the ISL6307B is reset. Cycling the
voltage on EN_PWR, EN_VTT or VCC below the POR-
falling threshold will reset the controller. Cycling the VID
codes will not reset the controller.
Overcurrent Protection
ISL6307B has two levels of overcurrent protection. Each
phase is protected from a sustained overcurrent condition on
a delayed basis, while the combined phase currents are
protected on an instantaneous basis.
In instantaneous protection mode, the ISL6307B takes
advantage of the proportionality between the load current
and the average current, I
condition. See the Channel-Current Balance section for
more detail on how the average current is measured. The
average current is continually compared with a constant
100µA reference current as shown in Figure 12. Once the
average current exceeds the reference current, a
comparator triggers the converter to shutdown.
In individual overcurrent protection mode, the ISL6307B
continuously compares the current of each channel with the
same 100µA reference current. If any channel current
exceeds the reference current continuously for eight
consecutive cycles, the comparator triggers the converter to
shutdown.
The overcurrent protection level for the above two OCP
modes can be adjusted by changing the value of current
sensing resistors. In addition, ISL6307 can also adjust the
average OCP threshold level by adjusting the value of the
resistor from IOUT to GND. This provides additional safety
for the voltage regulator.
The following equation can be used to calculate the value of
the resistor R
OCP2
R
IOUT
.
=
-------------------------------
I
AVG OCP2
IOUT
,
2
based on the desired OCP level I
AVG
23
, to detect an overcurrent
AVG,
(EQ. 17)
ISL6307B
At the beginning of overcurrent shutdown, the controller
places all PWM signals in a high-impedance state within
20ns commanding the Intersil MOSFET driver ICs to turn off
both upper and lower MOSFETs. The system remains in this
state a period of 4096 switching cycles. If the controller is still
enabled at the end of this wait period, it will attempt a soft-
start. If the fault remains, the trip-retry cycles will continue
indefinitely (as shown in Figure 13) until either controller is
disabled or the fault is cleared. Note that the energy
delivered during trip-retry cycling is much less than during
full-load operation, so there, there is no thermal hazard
during this kind of operation.
Current Sense Output
The ISL6307B has 2 current sense output pins IDROOP and
IOUT; they are identical. In typical application, IDROOP pin
is connected to FB pin for the application where load line is
required. IOUT pin was designed for load current
measurement. As shown in typical application schematics
on pages 4 to 7, load current information can be obtained by
measuring the voltage at IOUT pin with a resistor connecting
IOUT PIN to ground. When the programmable temperature
compensation function of ISL6307B is properly used, the
output current at IOUT pin is proportional to load current as
shown in Figure 14.
FIGURE 13. OVERCURRENT BEHAVIOR IN HICCUP MODE.
0A
0V
OUTPUT CURRENT, 50A/DIV
F
OUTPUT VOLTAGE,
500mV/DIV
SW
= 500kHz
2ms/DIV
March 9, 2006
FN9225.0