參數(shù)資料
型號: ISL6552CRZ
廠商: INTERSIL CORP
元件分類: 穩(wěn)壓器
英文描述: Microprocessor CORE Voltage Regulator Multi-Phase Buck PWM Controller
中文描述: SWITCHING CONTROLLER, 1500 kHz SWITCHING FREQ-MAX, PQCC20
封裝: 5 X 5 MM, PLASTIC, MO-220VHHC, QFN-20
文件頁數(shù): 13/18頁
文件大?。?/td> 421K
代理商: ISL6552CRZ
13
controller is under full load. This droop compensation allows
larger transient voltage deviations and thus reduces the size
and cost of the output filter components.
R
IN
should be selected to give the desired “droop” voltage at
the normal full load current 50
μ
A applied through the R
ISEN
resistor (or at a different full load current if adjusted as
outlined in the Over-Current, Selecting R
ISEN
section).
R
IN
= Vdroop/50
μ
A
For a Vdroop of 80mV, R
IN
= 1.6k
The AC feedback components, R
FB
and Cc, are scaled in
relation to R
IN
.
Current Balancing
The detected currents are also used to balance the phase
currents.
Each phase’s current is compared to the average of all
phase currents, and the difference is used to create an offset
in that phase’s PWM comparator. The offset is in a direction
to reduce the imbalance.
The balancing circuit can not make up for a difference in
r
DS(ON)
between synchronous rectifiers. If a FET has a higher
r
DS(ON)
, the current through that phase will be reduced.
Figures 8 and 9 show the inductor current of a two phase
system without and with current balancing.
Inductor Current
The inductor current in each phase of a multi-phase Buck
converter has two components. There is a current equal to
the load current divided by the number of phases (I
LT
/ n),
and a sawtooth current, (i
PK-PK
) resulting from switching.
The sawtooth component is dependent on the size of the
inductors, the switching frequency of each phase, and the
values of the input and output voltage. Ignoring secondary
effects, such as series resistance, the peak to peak value of
the sawtooth current can be described by:
i
PK-PK
= (V
IN
x V
CORE
- V
CORE2
)/(L
x F
SW
x V
IN
)
Where:
V
CORE
= DC value of the output or V
ID
voltage
V
IN
= DC value of the input or supply voltage
L = value of the inductor
F
SW
= switching frequency
Example: For V
CORE
= 1.6V,
V
IN
= 12V,
L = 1.3
μ
H,
F
SW
= 250kHz,
Then i
PK-PK
= 4.3A
The inductor, or load current, flows alternately from V
IN
through Q1 and from ground through Q2. The ISL6552
samples the on-state voltage drop across each Q2 transistor
to indicate the inductor current in that phase. The voltage
drop is sampled 1/3 of a switching period, i/F
SW
, after Q1 is
turned OFF and Q2 is turned on. Because of the sawtooth
current component, the sampled current is different from the
average current per phase. Neglecting secondary effects,
the sampled current (I
SAMPLE
) can be related to the load
current (I
LT
) by:
I
SAMPLE
=
I
LT
/ n +
(V
IN
V
CORE
-3V
CORE2
)/(6L x
F
SW
x V
IN
)
Where:
I
LT
= total load current
n = the number of channels
Example: Using the previously given conditions, and
For
I
LT
= 100A,
n = 4
Then
I
SAMPLE
= 25.49A
As discussed previously, the voltage drop across each Q2
transistor at the point in time when current is sampled is
r
DSON
(Q2) x
I
SAMPLE
. The voltage at Q2’s drain, the
PHASE node, is applied through the R
ISEN
resistor to the
ISL6552 ISEN pin. This pin is held at virtual ground, so the
current into ISEN is:
I
SENSE
= I
SAMPLE
x r
DS(ON)
(Q2)/R
ISEN
.
R
Isen
= I
SAMPLE
x r
DS(ON)
(Q2)/50
μ
A
0
5
10
15
20
25
A
FIGURE 8. TWO CHANNEL MULTI-PHASE SYSTEM WITH
CURRENT BALANCING DISABLED
0
5
10
15
20
25
A
FIGURE 9. TWO CHANNEL MULTI-PHASE SYSTEM WITH
CURRENT BALANCING ENABLED
ISL6552
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