isl6307b Intersil Corporation, isl6307b Datasheet - Page 22

• 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

determined by the frequency of the soft-start oscillator which
is defined by the resistor Rss from SS pin to GND. The 2
soft-start ramp times, Assuming the output voltage is 0V
before soft-start, TD2 and TD4 can be calculated based on
the following equations.
For example, when VID is set to 1.5V and the Rss is set at
100kΩ, the first soft-start ramp time TD2 will be 704µs and
the second soft-start ramp time TD4 will be 256µs.
Fault Monitoring and Protection
The ISL6307B actively monitors output voltage and current
to detect fault conditions. Fault monitors trigger protective
measures to prevent damage to a microprocessor load. One
common power good indicator is provided for linking to
external system monitors. The schematic in Figure 12
outlines the interaction between the fault monitors and the
power good signal.
VR_RDY Signal
The VR_RDY pin is an open-drain logic output to indicate
that the soft-start period is completed and the output voltage
is within the regulated range. VR_RDY is pulled low during
shutdown and releases high after a successful soft-start and
a fix delay time, TD5. TD5 is fixed delay with typical value at
85µs. VR_RDY will be pulled low when an undervoltage or
overvoltage condition is detected, or the controller is
disabled by a reset from EN_PWR, EN_VTT, POR, or VID
OFF-code.
TD2
TD4
=
=
1.1xR
----------------------- - µs
(
------------------------------------------------ µs
6.25x25
V
VID
VR_RDY, 5V/DIV
FIGURE 11. SOFT-START WAVEFORMS
6.25x25
SS
–
1.1
VOUT, 500mV/DIV
(
TD1
)xR
)
SS
(
TD2
)
EN_VTT, 1V/DIV
500µs/DIV
22
TD3 TD4
TD5
(EQ. 15)
(EQ. 16)
ISL6307B
Undervoltage Detection
The undervoltage threshold is set at 50% of the VID voltage.
When the output voltage at VSEN is below the undervoltage
threshold, VR_RDY gets pulled low. When the output
voltage comes back to 60% of the VID voltage, VR_RDY will
return back to high.
Overvoltage Protection
Regardless of the VR being enabled or not, the ISL6307B
overvoltage protection (OVP) circuit will be active after its
POR. The OVP thresholds are different under different
operation conditions. When VR is not enabled and before
the 2nd soft-start, the OVP threshold is 1.275V. Once the
controller detects a valid VID input, the OVP trip point will be
changed to the VID voltage plus 175mV.
Two actions are taken by the ISL6307B to protect the
microprocessor load when an overvoltage condition occurs.
At the inception of an overvoltage event, all PWM outputs
are commanded low instantly (less than 20ns) until the
voltage at VDIFF falls below 0.4V. This causes the Intersil
drivers to turn on the lower MOSFETs and pull the output
voltage below a level that might cause damage to the load.
The PWM outputs remain low until VDIFF falls below 0.4V,
and then PWM signals enter a high-impedance state. The
Intersil drivers respond to the high-impedance input by
turning off both upper and lower MOSFETs. If the
overvoltage condition reoccurs, the ISL6307B will again
command the lower MOSFETs to turn on. The ISL6307B will
continue to protect the load in this fashion as long as the
overvoltage condition recurs.
VDIFF
FIGURE 12. POWER GOOD AND PROTECTION CIRCUITRY
REFERENCE
DAC
50%
VID + 0.175V
UV
AND CONTROL LOGIC
+
-
SOFT-START, FAULT
OV
EACH CHANNEL
REPEAT FOR
OC2
OC
+
-
+
-
I
OC1
AVG
2V
+
-
100µA
I
R IOUT
1
March 9, 2006
VR_RDY
100µA
I
OVP
AVG
IOUT
FN9225.0