ISL6223 Datasheet, PDF (13/15 Pages) Intersil Corporation – Mobile Microprocessor CORE Voltage Regulator Multi-Phase Buck PWM Controller

ISL6223
+5V_IN
C_BP
C_T
R_FB
LOCATE NEXT
TO FB PIN
R_IN
+12V
C_BP
LOCATE NEXT TO IC PIN(S)
V_CC
PWM
COMP FS/DIS
ISL6223
R_T
VCC PVCC
HIP6601
FB
VSEN
LOCATE NEXT TO IC PIN
R_SEN
ISEN
USE INDIVIDUAL METAL RUNS
FOR EACH CHANNEL TO HELP
ISOLATE OUTPUT STAGES
C_BOOT
PHASE
C_IN
L_O1
LOCATE NEAR TRANSISTOR
V_CORE
C_OUT
KEY
ISLAND ON POWER PLANE LAYER
ISLAND ON CIRCUIT PLANE LAYER
VIA CONNECTION TO GROUND PLANE
FIGURE 12. PRINTED CIRCUIT BOARD POWER PLANES AND ISLANDS
Component Selection Guidelines
Output Capacitor Selection
The output capacitor is selected to meet both the dynamic
load requirements and the voltage ripple requirements. The
load transient for the microprocessor CORE is characterized
by high slew rate (di/dt) current demands. In general,
multiple high quality capacitors of different size and dielectric
are paralleled to meet the design constraints.
Modern microprocessors produce severe transient load rates.
High frequency capacitors supply the initially transient current
and slow the load rate-of-change seen by the bulk capacitors.
The bulk filter capacitor values are generally determined by
the ESR (effective series resistance) and voltage rating
requirements rather than actual capacitance requirements.
High frequency decoupling capacitors should be placed as
close to the power pins of the load as physically possible. Be
careful not to add inductance in the circuit board wiring that
could cancel the usefulness of these low inductance
components. Consult with the manufacturer of the load on
specific decoupling requirements.
Use only specialized low-ESR capacitors intended for
switching-regulator applications for the bulk capacitors. The
bulk capacitor’s ESR determines the output ripple voltage
and the initial voltage drop following a high slew-rate
transient’s edge. In most cases, multiple capacitors of small
case size perform better than a single large case capacitor.
Bulk capacitor choices include aluminum electrolytic, OS-
Con, Tantalum and even ceramic dielectrics. An aluminum
electrolytic capacitor’s ESR value is related to the case size
with lower ESR available in larger case sizes. However, the
equivalent series inductance (ESL) of these capacitors
increases with case size and can reduce the usefulness of
the capacitor to high slew-rate transient loading.
Unfortunately, ESL is not a specified parameter. Consult the
capacitor manufacturer and measure the capacitor’s
impedance with frequency to select a suitable component.
For surface mount designs, solid tantalum capacitors or
Panasonic Speciality Polymer (SP) capacitors can be used.
Output Inductor Selection
One of the parameters limiting the converter’s response to a
load transient is the time required to change the inductor
current. Small inductors in a multi-phase converter reduces
the response time without significant increases in total ripple
current.
The output inductor of each power channel controls the
ripple current. The control IC is stable for channel ripple
current (peak-to-peak) up to twice the average current. A
single channel’s ripple current is approximately:
∆I
=
-^V----^I--^N-----–----^V-----^O----^U----^T--
F_SWxL
×
-^V----^O----^U----^T--
V_IN
1.0
SINGLE
0.8
CHANNEL
0.6
0.4
3 CHANNEL
0.2
4 CHANNEL
2 CHANNEL
0
0
0.1
0.2
0.3
0.4
0.5
DUTY CYCLE (V_O/V_IN)
FIGURE 13. RIPPLE CURRENT vs DUTY CYCLE
13