ISL6261A Datasheet, PDF (16/34 Pages) Intersil Corporation – Single-Phase Core Regulator for IMVP-6 Mobile CPUs

ISL6261A
Protection
The ISL6261A provides overcurrent (OC), overvoltage (OV),
undervoltage (UV) and over-temperature (OT) protections as
shown in Table 3.
Overcurrent is detected through the droop voltage, which is
designed as described in the “Component Selection and
Application” section. The OCSET resistor sets the
overcurrent protection level. An overcurrent fault will be
declared when the droop voltage exceeds the overcurrent
set point for more than 120µs. A way-overcurrent fault will be
declared in less than 2µs when the droop voltage exceeds
twice the overcurrent set point. In both cases, the UGATE
and LGATE outputs will be tri-stated and PGOOD will go low.
The overcurrent condition is detected through the droop
voltage. The droop voltage is equal to I_core × R_droop, where
R_droop is the load line slope. A 10μA current source flows out
of the OCSET pin and creates a voltage drop across R_OCSET
(shown as R₁₀ in Figure 2). Overcurrent is detected when
the droop voltage exceeds the voltage across R_OCSET.
Equation 1 gives the selection of R_OCSET.
R_OCSET
=
I _OC × R_droop
10μA
(EQ. 1)
For example: The desired overcurrent trip level, I_oc, is 30A,
R_droop is 2.1mΩ, Equation 1 gives R_OCSET = 6.3k.
Undervoltage protection is independent of the overcurrent
limit. A UV fault is declared when the output voltage is lower
than (VID-300mV) for more than 1ms. The gate driver outputs
will be tri-stated and PGOOD will go low. Note that a practical
core regulator design usually trips OC before it trips UV.
There are two levels of overvoltage protection and response.
An OV fault is declared when the output voltage exceeds the
VID by +200mV for more than 1ms. The gate driver outputs
will be tri-stated and PGOOD will go low. The inductor
current will decay through the low-side FET body diode.
Toggling of VR_ON or bringing VDD below 4V will reset the
fault latch. A way-overvoltage (WOV) fault is declared
immediately when the output voltage exceeds 1.7V. The
ISL6261A will latch PGOOD low and turn on the low-side
FETs. The low-side FETs will remain on until the output
voltage drops below approximately 0.85V, then all the FETs
are turned off. If the output voltage again rises above 1.7V,
the protection process repeats. This mechanism provides
maximum protection against a shorted high-side FET while
preventing the output from ringing below ground. Toggling
VR_ON cannot reset the WOV protection; recycling VDD will
reset it. The WOV detector is active all the time, even when
other faults are declared, so the processor is still protected
against the high-side FET leakage while the FETs are
commanded off.
The ISL6261A has a thermal throttling feature. If the voltage
on the NTC pin goes below the 1.2V over-temperature
threshold, the VR_TT# pin is pulled low indicating the need
for thermal throttling to the system oversight processor. No
other action is taken within the ISL6261A.
Component Selection and Application
Soft-Start and Mode Change Slew Rates
The ISL6261A commands two different output voltage slew
rates for various modes of operation. The slow slew rate
reduces the inrush current during start-up and the audible noise
during the entry and the exit of Deeper Sleep Mode. The fast
slew rate enhances the system performance by achieving
active mode regulation quickly during the exit of Deeper Sleep
Mode. The SOFT current is bidirectional-charging the SOFT
capacitor when the output voltage is commanded to rise, and
discharging the SOFT capacitor when the output voltage is
commanded to fall.
Figure 5 shows the circuitry on the SOFT pin. The SOFT pin,
the non-inverting input of the error amplifier, is connected to
ground through capacitor C_SOFT. I_SS is an internal current
source connected to the SOFT pin to charge or discharge
C_SOFT. The ISL6261A controls the output voltage slew rate
by connecting or disconnecting another internal current
source I_Z to the SOFT pin, depending on the state of the
system, i.e. Start-up or Active mode, and the logic state on
the DPRSLPVR pin. The SOFT-START CURRENT section
of the Electrical Specification Table shows the specs of these
two current sources.
I
I
SS
Z
INTERNAL TO
ISL6261A
ERROR
AMPLIFLIER
C
SOFT
V
REF
FIGURE 5. SOFT PIN CURRENT SOURCES FOR FAST AND
SLOW SLEW RATES
I_SS is 41µA typical and is used during start-up and mode
changes. When connected to the SOFT pin, I_Z adds to I_SS to
get a larger current, labeled I_GV in the “Electrical
Specification Table” starting on page 3, on the SOFT pin. I_GV
is typically 200µA with a minimum of 175µA.
16
FN6354.3
November 5, 2009