ISL6398 Datasheet, PDF (14/57 Pages) Intersil Corporation – Programmable soft-start rate and DVID rate

ISL6398
Functional Pin Descriptions
Refer to Table 19 on page 53 for Design and Layout
Considerations.
VCC - Supplies the power necessary to operate the chip. Connect
this pin directly to a +5V supply with a high quality ceramic
bypass capacitor. The controller start to operate, when the
voltage on this pin exceeds the rising POR threshold and shuts
down when the voltage on this pin drops below the falling POR
threshold.
GND - The bottom metal base of ISL6398 is return of VCC supply.
It is also the return of the PMBus as well as all PWM output
drivers. Connect it to system ground; also externally connect pins
13, 14, and 15 to system GND.
ISENIN+, ISENIN- - These pins are current sense inputs to the
differential amplifier of the input supply. The sensed current is
used for input power monitoring and power management of the
system. When not used, connect ISENIN+ to VIN and a resistor
divider with a ratio of 1/3 on ISENIN± pin, say 499kΩ in between
ISENIN± pins and then 1.5MΩ from ISENIN- to ground
(see Figure 29). Refer to “Input Current Sensing” on page 30 for
configuration details. Regardless input current sense is used or
not, ISENIN+ should be connected to input voltage (V_IN) for
feed-forward compensation to maintain a constant loop gain
over the input line variation.
EN_PWR_CFP - This pin is a threshold-sensitive enable input and
a catastrophic failure protection (CFP) output. Connecting the
power train input supply to this through an appropriate resistor
divider provides input undervoltage protection and a means to
synchronize the power sequencing of the controller and the
MOSFET driver ICs. When EN_PWR_CFP is driven above 0.85V
but below 3.3V, the controller is actively depending on status of
the TM_EN_OTP, the internal POR, and pending fault states.
Driving EN_PWR_CFP below 0.75V or above 3.7V will turn off the
controller, clear all fault states (except for CFP fault) and prepare
the ISL6398 to soft-start when re-enabled. In addition, this pin
will be latched high (VCC) by the input overcurrent (monitored by
ISENIN±) or VR overvoltage event. The latch resets by cycling VCC
and cannot reset by TM_EN_OTP or EN_PWR_CFP since when the
catastrophic failure (CFP) is triggered, the input power is
removed from VR so is the VTT voltage rail and it is PGOOD
signal. To keep CFP active, VCC should be biased with a standby
supply. This feature means to provide protection to the case that
the VR with shorted high-side MOSFET draws insufficient current
to trigger the input supply’s over current trip level, this pin will
send an active high signal (CFP) to disconnect the input supply
before catching fire or further damage of PCB. Refer
“Catastrophic Fault Protection” on page 30 for more details.
VSEN_OVP - This pin monitors the regulator output for
overvoltage protection. Connect this pin to the positive rail
remote sensing point of the microprocessor or load. This pin
tracks with the VSEN pin. If a resistive divider is placed on the
VSEN pin, a resistive divider with the same ratio should be placed
on the VSEN_OVP pin to track UVP and OVP.
VSEN - This pin compensates the voltage drop between the load
and local output rail for precision regulation. Connect this pin to
the positive rail remote sensing point of the microprocessor or
load. It also is the APA level sensing input.
RGND - This pin compensates the offset between the remote
ground of the load and the local ground of this device for
precision regulation. Connect this pin to the negative rail remote
sensing point of the microprocessor or load.
VR_RDY - VR_RDY indicates that soft-start has completed and the
output remains in normal operation. It is an open-drain logic output.
When OCP, UVP, OVP, or CFP occurs, VR_RDY is pulled low.
TM_EN_OTP - Input pin for the temperature measurement.
Connect this pin through an NTC thermistor to GND and a resistor
to VCC of the controller. The voltage at this pin is inversely
proportional to the VR temperature. The device monitors the VR
temperature based on the voltage at the TM pin. Combined with
“TCOMP” setting, the sensed current is thermally compensated.
The VR_HOT# asserts low if the sensed temperature at this pin is
higher than the maximum desired temperature, “TMAX”. The NTC
should be placed close to the current sensing element, the output
inductor or dedicated sense resistor on Phase 1. A decoupling
capacitor (0.1µF) is typically needed in close proximity to the
controller. In addition, the controller is disabled when this pin’s
voltage drops below 0.95 (typically) and is active when it is above
1.05V (typically); it can serve as Enable and Over-Temperature
functions, however, when it is used as an Enable toggle input,
bit2 of STATUS_BYTE (78h) will flag OT; CLEAR_FAULTS (03h)
command must be sent to clear the fault after VR start-up. If not
used, connect a 1MΩ/2MΩ resistor divider or tie to V_CC.
PWM[6:1] - Pulse width modulation outputs. Connect these pins
to the PWM input pins of the Intersil driver IC(s). The number of
active channels is determined by the state of PWM[6:2]. Tie
PWM(N+1) to VCC to configure for N-phase operation. The PWM
firing order is sequential from 1 to N with N being the number of
active phases. If PWM1 is tied high, the VR is disabled.
ISEN[6:1]+, ISEN[6:1] - The ISEN+ and ISEN- pins are current
sense inputs to individual differential amplifiers of VR. The
sensed current is used for channel current balancing, overcurrent
protection, and droop regulation. Inactive channels should have
their respective current sense inputs, ISEN[6:#]- grounded, and
ISEN[6:#]+ open. For example, ground ISEN[6:5]- and open
ISEN[6:5]+ for 4-phase operation. DO NOT ground ISEN[6:1]+. For
DCR sensing, connect each ISEN- pin to the node between the RC
sense elements. Tie the ISEN+ pin to the other end of the sense
capacitor (typically output rail). The voltage across the sense
capacitor is proportional to the inductor current. Therefore, the
sensed current is proportional to the inductor current and scaled
by the DCR of the inductor and R_SET.
BUF_COMP - Buffered output of internal COMP.
VR_HOT# - Indicator of VR temperature reaching above TMAX set
by PMBus E8[2:0]. It is an open-drain logic output. Normally open
if the measured VR temperature is less than TMAX, and pulled
low when the measured VR temperature exceeds TMAX.
RSET - A resistor connected from this pin to ground sets the
current gain of the current sensing amplifier. The RSET resistor
value can be set from 3.84k to 60.4k and is 64x of the
equivalent R_ISEN resistor value. Therefore, the effective current
sense resistor value can be set between 60 and 943.
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FN8575.1
August 13, 2015