ISL6398 Datasheet, PDF (26/57 Pages) Intersil Corporation – Programmable soft-start rate and DVID rate

ISL6398
To deal with layout and design variation of different platforms,
the ISL6398 is intentionally trimmed to negative range at no
load, thus, an offset can easily be added to calibrate the digitized
IMON reading (8Ch in PMBus) whenever needed by PMBus (E4h)
or the external pull-up resistor in Figure 16. Hence, the slope on
the IMON pin is set by the equivalent impedance of
R_MON1//R_MON2 =R_IMON. Additional offset can be added by
IOUT_CAL_OFFSET (E5h).
R_MON2 = _V-----I--_M----_O-----_N----_{_}-V--_O---^C--_F--^C-_F----_S^R----_E-^I--^M-_T---^O-_{_}---_D-^N---_E----_S----_I--_R----_E----_D--
R_MON1 = --R---R-_I--_M-^I--^M--_O---^O-_N---^N--₂--²--_–---R---R--^I-^M-_I--_M--^O---_O--^N---_N--
(EQ. 18)
ISL6398
EXTERNAL CIRCUIT
V_CC
Two actions are taken by ISL6398 to protect the load when an
overvoltage condition occurs.
At the inception of an overvoltage event, all PWM outputs are
commanded low instantly. This causes the Intersil drivers to turn on
the lower MOSFETs and pull the output voltage below a level to avoid
damaging the load. When the output voltage falls below the DAC
plus 100mV, 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
ISL6398 will again command the lower MOSFETs to turn on. The
ISL6398 will continue to protect the load in this fashion as long as
the overvoltage condition occurs.
Once an overvoltage condition is detected, the respective VR
ceases the normal PWM operation and pulls its VR_Ready low
until the ISL6398 is reset. Cycling the voltage V_CC below the
POR-falling threshold will reset the controller. Cycling
EN_PWR_CFP or TM_EN_OTP will NOT reset the controller.
PMBus DIGITIZED IOUT (8Ch)
R_{MON 2} = #MΩ
IMON
R_MON1 = #kΩ
VSEN _{OPEN SENSE}
RGND PROTECTION
VR_RDY
+
OC
-
100µA*F4[3:0]
I_AVG
FIGURE 16. IMON NO LOAD OFFSET CALIBRATION
In addition, if the IMON pin voltage is higher than 3.0V,
overcurrent shutdown will be triggered, as described in
“Overcurrent Protection” on page 27.
Fault Monitoring and Protection
The ISL6398 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 (VR_RDY) is provided for linking to external
system monitors. The schematic in Figure 17 outlines the
interaction between the fault monitors and the VR_RDY signal.
VR_Ready Signal
The VR_RDY pin is an open-drain logic output which indicates
that the soft-start period is complete and the output voltage is
within the regulated range. The VR_RDY is pulled low during
shutdown and releases high after a successful soft-start. VR_RDY
will be pulled low when an fault (OCP, OTP, UVP, or OVP) condition
is detected, or the controller is disabled by a reset from
EN_PWR_CFP, TM_EN_OTP, POR, or VID OFF-code.
Overvoltage Protection
Regardless of the VR being enabled or not, the ISL6398
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 during the soft-start intervals t_D1, the
OVP threshold is programmable via PMBus (D8h[4:3]). Once the
VR completes the soft-start, the OVP trip point will change to a
tracking level of DAC+OVP, programmable via PMBus (D8h[2:0]).
SOFT-START, FAULT
AND CONTROL LOGIC
VSEN_OVP
PRE_OVP
D8[4:3]
+
OV
-
VID + OVP
D8[2:3]
ISL6398
+
OC
-
3.0V
IMON
FIGURE 17. VR_RDY AND PROTECTION CIRCUITRY
In addition, the ISL6398 features open sensing protection to
detect an open of the output voltage sensing as an OVP event,
which suspends the controller operation. Without this protection,
the VR can regulate up to maximum duty cycle and damage the
load and power trains when the output sensing is broken open.
Furthermore, since the regulation loop is sensed via the VSEN pin
and the OVP is sensed via the VSEN_OVP pin, they are
independent paths to keep output within target and below OVP
level, respectively. Thus, the ISL6398 protects against a single
point of failure.
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FN8575.1
August 13, 2015