ISL70003SEH Datasheet, PDF (21/32 Pages) Intersil Corporation – Acceptance tested to 50krad

ISL70003SEH
logic activates the power blocks, the regulator ramps the output
voltage to its set value within a soft-start interval, however, the
device no longer goes through the preinitialization phase.
Transitions between the number of active LXx pins through the
use of SEL1 and SEL2 should not be done while the part is
operating. On the fly transitions will cause glitches on the output
voltage which may exceed transient requirements. It is
recommended to place the ISL70003SEH in standby mode, by
pulling SEL1 and SEL2 HIGH, and then change the number of
active LXx pins.
The overcurrent trip point scales depending on the number of
active power blocks. Equation 10 may be used to determine the
value of R_OCSETA and R_OCSETB when less than 10 power blocks
are active:
R_{OCSETA B} = ³----⁶---⁰-_I--_O²----^._C-⁴----_P-^-----^N---
(EQ. 10)
Where N is the number of active phases.
IMON Current Sense Output
The ISL70003SEH provides a current monitor function through
IMON. Current monitoring informs designers if down steam loads
are operating as expected. It is also useful in the prototype and
debug phase of the design and during normal operation to
measure the overall performance of a system. The IMON pin
outputs a high speed analog current source that is proportional
to the sensed peak current through the ISL70003SEH. In typical
applications, a resistor R_IMON is connected to the IMON pin to
convert the sensed current to voltage, V_IMON, which is
proportional to the peak current, as shown in Equation 11:
V_IMON = 100  10^–6  ^I--^S----^A----^M-----^P----^L---^E--_N---^-----^R-----^I-^M-----^O-----^N--
(EQ. 11)
where V_IMON is the voltage at the IMON pin, R_IMON is the resistor
between the IMON pin and AGND, I_SAMPLE is the current through
the converter at the time IMON samples the current, and N is the
number of active power blocks. I_SAMPLE may be calculated from
Equation 12.
I_SAMPLE
=
I_LO
A
D
+
_--2---I
–



I

t_{--S----A----M-----1P----L-–--E--D---}_-----f_{--S----W---}
(EQ. 12)
Where t_SAMPLE is the time it takes the IMON circuitry to sample
the current (300ns, max.), I_LOAD is the load current and ΔI is the
inductor peak-to-peak ripple current as calculated in Equation 7.
A small capacitor should be placed between the IMON pin and
AGND to reduce the noise impact and mitigate single event
transients. If this pin is not used, it is best connected to VREFA. It
is also acceptable to tie to GND through a resistor.
Figures 42 and 43 show the response of the IMON current
monitor due to a load step with a R_IMON = 10kΩ and 100pF
ceramic capacitor in parallel.
VIMON VOLTAGE
200mV/DIV
INDUCTOR
CURRENT
2A/DIV
TIME (5µs/DIV)
FIGURE 42. IMON RESPONSE TO 6A LOAD STEP
VIMON VOLTAGE
200mV/DIV
INDUCTOR
CURRENT
2A/DIV
TIME (5µs/DIV)
FIGURE 43. IMON RESPONSE TO 6A LOAD RELEASE
It is important to note that if the on time of the lower NMOS FET
is shorter than the IMON current sense time (300ns max), the
IMON output is tri-stated after 4 consecutive failed sense
occurrences.
Diode Emulation
Diode Emulation (DE) allows for higher converter efficiency under
light load situations. In DE mode, the low-side MOSFET conducts
when the current is flowing from source to drain and does not
allow reverse current, emulating a diode. As shown in Figure 44,
when the LGATE signal is HIGH, the low-side MOSFET carries
current, creating negative voltage on the phase node due to the
voltage drop across the ON-resistance. When the DE pin is pulled
HIGH, the ISL70003SEH will be in diode emulation mode and
detect the zero current crossing of the inductor current and turn
off the lower MOSFET to prevent the inductor current from
reversing direction and creating unnecessary power loss. This
ensures that Discontinuous Conduction Mode (DCM) is achieved.
Since diode emulation prevents the low-side MOSFET from
sinking current, no negative spike at the output is generated
during pre-biased startup when DE mode is active.
After a significantly fast load release transient, diode emulation
will not allow the converter to bring the output voltage back down
following the hump created by the inductor energy dump into the
output capacitor bank. The ISL70003SEH overcomes this issue
by monitoring the output of the error amplifier and allowing the
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FN8604.5
May 12, 2016