參數(shù)資料
型號: ISL6553CB
廠商: INTERSIL CORP
元件分類: 穩(wěn)壓器
英文描述: PWM Controller with Wide Input Range 8-PDIP -25 to 85
中文描述: SWITCHING CONTROLLER, 1500 kHz SWITCHING FREQ-MAX, PDSO16
封裝: PLASTIC, MS-012-AC, SOIC-16
文件頁數(shù): 10/15頁
文件大?。?/td> 182K
代理商: ISL6553CB
10
Current Sensing and Balancing
Overview
The ISL6553 samples the on-state voltage drop across each
synchronous rectifier FET, Q2, as an indication of the
inductor current in that phase, see Figure 7. Neglecting AC
effects (to be discussed later), the voltage drop across Q2 is
simply r
DS(ON)
(Q2) x inductor current (I
L
). Note that I
L
, the
inductor current, is 1/2 of the total current (I
LT
).
The voltage at Q2’s drain, the PHASE node, is applied to the
R
ISEN
resistor to develop the I
ISEN
current to the ISL6553
ISEN pin. This pin is held at virtual ground, so the current
through R
ISEN
is I
L
x r
DS(ON)
(Q2) / R
ISEN
.
The I
ISEN
current provides information to perform the
following functions:
1. Detection of an over-current condition
2. Reduce the regulator output voltage with increasing load
current (droop)
3. Balance the I
L
currents in the two phases
Over-Current, Selecting R
ISEN
The current detected through the R
ISEN
resistor is averaged
with the current detected in the other channel. The averaged
current is compared with a trimmed, internally generated
current, and used to detect an over-current condition.
The nominal current through the R
ISEN
resistor should be
50
μ
A at full output load current, and the nominal trip point for
over-current 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 over-current trip point would be 165% of 25A, or ~ 41A
per phase. The R
ISEN
value can be adjusted to change the
over-current trip point, but it is suggested to stay within
±
25%
of nominal.
Droop, Selection of R
IN
The average of the currents detected through the R
ISEN
resistors is also steered to the FB pin. There is no DC return
path connected to the FB pin except for R
IN
, so the average
current creates a voltage drop across R
IN
. This drop
increases the apparent V
CORE
voltage with increasing load
current, causing the system to decrease V
CORE
to maintain
balance at the FB pin. This is the desired “droop” voltage
used to maintain V
CORE
within limits under transient
conditions.
FIGURE 7. SIMPLIFIED FUNCTIONAL BLOCK DIAGRAM SHOWING CURRENT AND VOLTAGE SAMPLING
CURRENT
SENSING
COMPARATOR
PWM
CIRCUIT
AVERAGING
CURRENT
SENSING
FROM
OTHER
CHANNEL
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
PHASE
INDUCTOR
CURRENT
FROM
OTHER
CHANNEL
PWM
I
L
ISL6553
C
O
R
L
V
IN
ONLY ONE OUTPUT
STAGE SHOWN
HIP6601
-
-
-
+
-
+
-
+
ISL6553
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