ISL6217ACVZ-T Intersil, ISL6217ACVZ-T Datasheet - Page 17

• Manufacturer Part Number: ISL6217ACVZ-T
• Description: IC CTRLR PWM INTEL PENT 38-TSSOP
• Manufacturer: Intersil

Specifications of ISL6217ACVZ-T

• Applications: Controller, Intel Pentium® IMVP-IV, IMVP+
• Voltage - Input: 5.5 ~ 25 V
• Number Of Outputs: 1
• Operating Temperature: -10°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 38-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -

selected based on R
Equation 3, r
the following equation:
Diode Emulation
Diode emulation allows for higher converter efficiency under
light-load situations. With diode emulation active, the
ISL6217A will detect the zero current crossing of the output
inductor and turn off LGATE. This ensures that
discontinuous conduction mode (DCM) is achieved. In DCM,
conduction losses are reduced in the Low-Side MOSFET,
consequently boosting efficiency. The ISL6217A operates in
DCM in both deep and deeper sleep mode.
Adaptive Shoot-Through Protection
Both drivers incorporate adaptive shoot-through protection
to prevent upper and lower MOSFETs from conducting
simultaneously and shorting the input supply. This is
accomplished by ensuring the falling gate has turned off one
MOSFET before the other is allowed to turn on.
During turn-off of the lower MOSFET, the LGATE voltage is
monitored until it reaches a 1V threshold, at which time the
UGATE is released to rise. Adaptive shoot-through circuitry
monitors the upper MOSFET gate-to-source voltage during
UGATE turn-off. Once the upper MOSFET gate-to-source
voltage has dropped below a threshold of 1V, the LGATE is
allowed to rise.
Component Selection Guidelines
OUTPUT CAPACITOR SELECTION
Output capacitors are required to filter the output inductor
current ripple and supply the transient load current. The
filtering requirements are a function of the channel switching
frequency and the output ripple current. The load transient
requirements are a function of the slew rate (di/dt) and the
magnitude of the transient load current.
The microprocessor used for IMVP-IV™ and IMVP-IV+™
will produce transient load rates as high as 30A/ns. High
frequency, ceramic capacitors are used to supply the initial
transient current and slow the rate-of-change seen by the
bulk capacitors. Bulk filter capacitor values are generally
determined by the ESR (Effective Series Resistance) and
voltage rating requirements rather than actual capacitance
requirements. To meet the stringent requirements of
IMVP-IV™ and IMVP-IV+™, (15) 2.2µF, 0612 “Flip Chip”
high frequency, ceramic capacitors are placed very close the
Processor power pins, with care being taken not to add
inductance in the circuit board traces that could cancel the
usefulness of these low inductance components.
Specialized low-ESR capacitors, intended for switching
regulator applications, are recommended for the bulk
R
DROOP
=
2
DS(ON)
3 .
⋅
(
Droop
, and Droop as per the Block Diagram or
ISEN
)
⋅
which is calculated through
r
R
(
DSON
ISEN
17
M
)
(
Ω
)
(EQ. 6)
ISL6217A
capacitors. The bulk capacitor ESR and ESL determine the
output ripple voltage and the initial voltage drop following a
high slew-rate transient edge. Recommended are at least (4)
4V, 220µF Sanyo Sp-Cap capacitors in parallel, or (5) 330µF
SP-Cap style capacitors. These capacitors provide an
equivalent ESR of less than 3mΩ. These components
should be laid out very close to the load.
As the sense trace for VSEN may be long and routed close
to switching nodes, a 1.0µF ceramic decoupling capacitor is
located between VSEN and ground at the ISL6217A.
Output Inductor Selection
The output inductor is selected to meet the voltage ripple
requirements and minimize the converter response time to a
load transient. In a multi-phase converter topology, the ripple
current of one active channel partially cancels with the other
active channels to reduce the overall ripple current. The
reduction in total output ripple current results in a lower
overall output voltage ripple.
The inductor selected for the power channels determines the
channel ripple current. Increasing the value of inductance
reduces the total output ripple current and total output
voltage ripple; however, increasing the inductance value will
slow the converter response time to a load transient.
One of the parameters limiting the converter response time
to a load transient is the time required to slew the inductor
current from its initial current level to the transient current
level. During this interval, the difference between the two
levels must be supplied by the output capacitance.
Minimizing the response time can minimize the output
capacitance required.
The channel ripple can be reasonably approximated by the
following equation:
The total output ripple current can be approximated from the
curves in Figure 10.
They provide the total ripple current as a function of duty
cycle and number of active channels, normalized to the
parameter K NORM at zero duty cycle,
Where L is the channel inductor value.
K
∆
I
NORM
CH
=
V
=
IN
F
L
SW
V
−
•
OUT
F
V
SW
•
OUT
L
•
V
V
OUT
IN
June 30, 2005
(EQ. 8)
FN9107.3
(EQ. 7)