ISL6553 Intersil Corporation, ISL6553 Datasheet - Page 10

• Manufacturer Part Number: ISL6553
• Description: Microprocessor CORE Voltage Regulator Multi-Phase Buck PWM Controller
• Manufacturer: Intersil Corporation

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
inductor current, is 1/2 of the total current (I
The voltage at Q2’s drain, the PHASE node, is applied to the
R
ISEN pin. This pin is held at virtual ground, so the current
through R
The I
following functions:
Over-Current, Selecting R
The current detected through the R
with the current detected in the other channel. The averaged
1. Detection of an over-current condition
2. Reduce the regulator output voltage with increasing load
3. Balance the I
ISEN
current (droop)
ISEN
FB
resistor to develop the I
DS(ON)
ISEN
current provides information to perform the
CURRENT
TO OVER
REFERENCE
AMPLIFIER
FIGURE 7. SIMPLIFIED FUNCTIONAL BLOCK DIAGRAM SHOWING CURRENT AND VOLTAGE SAMPLING
(Q2) x inductor current (I
is I
R
ERROR
+
-
TRIP
FB
L
DAC
R
L
currents in the two phases
IN
x r
C
COMPARATOR
c
DS(ON)
CHANNELS
TO OTHER
COMP
10
(Q2) / R
GENERATOR
ISEN
SAWTOOTH
ISEN
CORRECTION
+
+
-
ISEN
current to the ISL6553
DIFFERENCE
-
ISEN
L
resistor is averaged
). Note that I
REFERENCE
-
.
LT
+
).
AVERAGING
COMPARATOR
+
-
L
, the
ISL6553
ISL6553
CURRENT
SENSING
CURRENT
SENSING
FROM
OTHER
CHANNEL
CIRCUIT
PWM
current is compared with a trimmed, internally generated
current, and used to detect an over-current condition.
The nominal current through the R
50 A at full output load current, and the nominal trip point for
over-current detection is 165% of that value, or 82.5 A.
Therefore, R
For a full load of 25A per phase, and an r
4m , R
The over-current trip point would be 165% of 25A, or ~ 41A
per phase. The R
over-current trip point, but it is suggested to stay within 25%
of nominal.
Droop, Selection of R
The average of the currents detected through the R
resistors is also steered to the FB pin. There is no DC return
path connected to the FB pin except for R
current creates a voltage drop across R
increases the apparent V
current, causing the system to decrease V
balance at the FB pin. This is the desired “droop” voltage
used to maintain V
conditions.
PWM
ISEN
ISEN
ISEN
= 2k .
ONLY ONE OUTPUT
HIP6601
ISEN
= I
CORE
L
STAGE SHOWN
R
x r
ISEN
value can be adjusted to change the
CORE
DS(ON)
within limits under transient
IN
INDUCTOR
Q2
CURRENT
CHANNEL
V
IN
OTHER
FROM
voltage with increasing load
Q1
(Q2) / 50 A.
ISEN
PHASE
L
I
L
IN
resistor should be
DS(ON)
IN
. This drop
CORE
, so the average
V
CORE
to maintain
(Q2) of
ISEN