參數(shù)資料
型號(hào): ISL6554CBZ
廠商: INTERSIL CORP
元件分類: 穩(wěn)壓器
英文描述: Microprocessor CORE Voltage Regulator Using Multi-Phase Buck PWM Control Without Programmable Droop
中文描述: SWITCHING CONTROLLER, 1500 kHz SWITCHING FREQ-MAX, PDSO20
封裝: PLASTIC, LEAD FREE, MS-013-AC, SOIC-20
文件頁(yè)數(shù): 11/16頁(yè)
文件大?。?/td> 492K
代理商: ISL6554CBZ
11
FN9003.3
February 11, 2005
The nominal current through the R
ISEN
resistor should be
50
μ
A at full output load current, and the nominal trip point for
overcurrent detection is 165% of that value, or 82.5
μ
A.
Therefore, R
ISEN
= I
L
x r
DS(ON)
(Q2) / 50
μ
A.
For a full load of 25A per phase, and an r
DS(ON)
(Q2) of
4m
, R
ISEN
= 2k
.
The overcurrent trip point would be 165% of 25A, or ~ 41A
per phase. The R
ISEN
value can be adjusted to change the
overcurrent trip point, but it is suggested to stay within
±
25%
of nominal.
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 ISL6554
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
FIGURE 7. SIMPLIFIED FUNCTIONAL BLOCK DIAGRAM SHOWING CURRENT AND VOLTAGE SAMPLING
CURRENT
SENSING
COMPARATOR
PWM
CIRCUIT
AVERAGING
CURRENT
SENSING
FROM
OTHER
CHANNELS
SAWTOOTH
GENERATOR
+
DIFFERENCE
R
ISEN
+
CORRECTION
ERROR
AMPLIFIER
FB
COMP
REFERENCE
DAC
TO OTHER
CHANNELS
ISEN
R
IN
R
FB
C
c
V
CORE
Q1
Q2
COMPARATOR
REFERENCE
TO OVER
CURRENT
TRIP
L
01
PHASE
INDUCTOR
CURRENT(S)
FROM
OTHER
CHANNELS
PWM
I
L
ISL6554
C
O
R
L
V
IN
ONLY ONE OUTPUT
STAGE SHOWN
HIP6601
-
+
-
+
-
+
-
ISL6554
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