ISL6336B Datasheet, PDF (21/31 Pages) Intersil Corporation – 6-Phase PWM Controller with Light Load Efficiency Enhancement and Current Monitoring

ISL6336B
IMON to offset for the tolerance at the maximum IMON
voltage value. This can be done by connecting a resistor
from the IMON pin to VCC as shown in Figure 11. The
required value for R_VCC can be determined by using
Equation 18:
R_VCC
=
R_{-----I--M-----O----N------}⋅_---(_--V_----C_-----C_{------–-----}V_{----I--M----O-----N----O-----F---S-----–-----}V_{----I--M-----O----N----M-----A----X----})
V_IMONOFS
(EQ. 18)
where R_IMON is the resistor from IMON to GND, V_IMONOFS
is the desired offset voltage at V_IMONMAX, and V_IMONMAX
is the voltage at IMON at the maximum load current.
For example, if the maximum IMON voltage is 900mV at full
load and the required offset voltage is 50mV and R_IMON is
10kΩ then R_VCC should be 810kΩ. R_IMON should be
connected to GND near the load to increase accuracy.
EXTERNAL CIRCUIT
V_CC
ISL6336B
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 ISL6336B 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 ISL6336B
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 ISL6336B 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 ISL6336B will again command the lower MOSFETs to turn
on. The ISL6336B 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 ISL6336B 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
ISL6336B 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 ISL6336B 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
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FN6696.2
August 31, 2010