ISL6336CRZ-T Datasheet, PDF (21/31 Pages) Intersil Corporation – 6-Phase PWM Controller with Light Load Efficiency Enhancement and Current Monitoring

ISL6336, ISL6336A
EXTERNAL CIRCUIT
V_CC
ISL6336, ISL6336A
INTERNAL CIRCUIT
R_VCC
IMON
R_IMON
C_IMON
+
V_IMON
-
I_AVG
NEAR LOAD GND
FIGURE 11. IMON RESISTOR DIVIDER
Fault Monitoring and Protection
The ISL6336, ISL6336A 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
VR_RDY signal.
VR_RDY
UV
50%
DAC
SOFT-START, FAULT
AND CONTROL LOGIC
-
OC
+
105µA
I_AVG
VDIFF
+
OV
-
-
OC
+
1.11V
I_MON
VID + 0.175V
FIGURE 12. VR_RDY AND PROTECTION CIRCUITRY
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 fixed delay time, t_D5 (see Figure 9). VR_RDY will be pulled
low when an undervoltage, overvoltage, or overcurrent
condition is detected, or if the controller is disabled by a
reset from EN_PWR, EN_VTT, POR, or VID OFF-code.
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 ISL6336,
ISL6336A 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 ISL6336, ISL6336A to protect
the microprocessor load when an overvoltage condition
occurs.
At the inception of an overvoltage event, all PWM outputs
are commanded low instantly (in less than 20ns). This
causes the Intersil drivers to turn on the lower MOSFETs and
pull the output voltage down to avoid damaging the load.
When the voltage at VDIFF falls below the DAC plus 75mV,
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 ISL6336, ISL6336A will again command the
lower MOSFETs to turn on. The ISL6336, ISL6336A will
continue to protect the load in this fashion as long as the
overvoltage condition occurs.
Once an overvoltage condition is detected, normal PWM
operation ceases until the ISL6336, ISL6336A 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
ISL6336, ISL6336A has two levels of overcurrent protection.
Each phase is protected from a sustained overcurrent
condition by limiting its peak current, while the combined
phase currents are protected on an instantaneous basis.
In instantaneous protection mode, the ISL6336, ISL6336A
utilizes the sensed average current I_AVG to detect an
overcurrent condition. See “Channel-Current Balance” on
page 15 for more detail on how the average current is
measured. The average current is continually compared with
a constant 105µA reference current, as shown in Figure 12.
Once the average current exceeds the reference current, a
comparator trips and causes the converter to shutdown.
The voltage at the IMON pin is used for average current
protection (compared to the instantaneous current protection
described above). The current out of the IMON pin is equal to
the sensed average current, I_AVG. With a resistor from IMON
to GND, the voltage at IMON will be proportional to the
21
FN6504.1
May 28, 2009