ISL6218CVZ-T Datasheet, PDF (15/19 Pages) Intersil Corporation – Precision Single-Phase Buck PWM Controller for Intel Mobile Voltage Positioning IMVP-IV and IMVP-IV

ISL6218
C2
R1
FB ^{R2 C1} COMP
CDCPL
VSEN
_
V _DROOP
+
EA+
RDROOP
SOFT
C _SOFT
ERROR
AMPLIFIER
-
-
+
+
V _ERROR1
COMPARATOR
I _DROOP
IMVP IV
REFERENCE
IOCSET
OVER-UNDER
VOLTAGE
PWM
CIRCUIT
OVER
CURRENT
ISEN’
ISL6218
ISEN
CURRENT
SENSING
UG1
LG1
ISEN1
ISEN1
RISEN
+ ^VrDS(ON)-
V _IN
PHASE
Q1 L01
-
Q2
VrDS(OINL1)
+
VCORE
COUT ^RLOAD
FIGURE 10. SIMPLIFIED BLOCK DIAGRAM OF THE ISL6218 VOLTAGE AND CURRENT CONTROL LOOPS FOR THE SINGLE CHANNEL
REGULATOR.
approximately ½ of the I_SEN, as shown in the “Block
Diagram” on page 7. The Droop current is sourced out of the
SOFT pin through the Droop resistor and returns through the
EA+ pin. This creates a “Droop” voltage V_DROOP, that
subtracts from the IMVP-IV^™ reference voltage on SOFT to
generate the voltage setpoint for the CORE regulator.
Full load current for the Intel IMVP-IV^™ Thin and Light
specification is 25A. Knowing that the Droop Current,
sourced out of the SOFT pin will be ½ of the I_SEN, a “Droop”
resistor, R_DROOP, can be selected to provide the amount of
voltage “Droop” required at full load. The selection of this
resistor is explained “Selection of RDROOP” on page 15.
SELECTION OF R_DROOP
Figure 11 shows a static “Droop” load line for the 1.484V
Active Mode. The ISL6218, as previously mentioned, allows
the programming of the load line slope by the selection of
the R_DROOP resistor.
As per the Intel IMVP-IV^™ and IMVP-IV+^™ specification,
Droop = 0.003 (Ω). Therefore, 25A of full load current
equates to a 0.075V Droop output voltage from the VID
setpoint. R_DROOP can be selected based on R_ISEN which is
calculated through Equation 3, r_(DS(ON) and Droop, as per
the “Block Diagram” on page 7 or Equation 6:
R_DROOP
=
2.3
⋅
(Droop) ⋅
R_ISEN
r_(DSON)
(Ω)
M
(EQ. 6)
VOUT, _HI
VOUT, _NOM
VOUT, _LO
(0A, 1.506V)
(0A, 1.484V)
(0A, 1.462V)
(25A, 1.431V)
(25A, 1.409V)
(25A, 1.387V)
-3m
LOAD LINE
IOUT, _NL
IOUT, _MID
IOUT, _MAX
STATIC TOLERANCE BANDS
NOMINAL "DROOP" LOAD LINE
FIGURE 11. IMVP-IV^™ ACTIVE MODE STATIC LOAD LINE
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^™ 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^™, (15) 2.2µF, 0612 “Flip
Chip” high frequency, ceramic capacitors are placed very close
15
FN9101.6
August 6, 2007