ISL6552CB Intersil, ISL6552CB Datasheet - Page 12

• Manufacturer Part Number: ISL6552CB
• Description: IC PWM CORE VOLTAGE REG 20-SOIC
• Manufacturer: Intersil

Specifications of ISL6552CB

• Pwm Type: Controller
• Number Of Outputs: 1
• Frequency - Max: 1.5MHz
• Voltage - Supply: 4.75 V ~ 5.25 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 20-SOIC (7.5mm Width)
• Frequency-max: 1.5MHz
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Duty Cycle: -

Current Sensing and Balancing
Overview
The ISL6552 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 either 1/2, 1/3, or 1/4 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
averaged with the current(s) detected in the other 1, 2, or 3
channels. The averaged current is compared with a
trimmed, internally generated current, and used to detect
an over-current condition.
1. Detection of an over-current condition
2. Reduce the regulator output voltage with increasing load
3. Balance the I
LT
ISEN
), depending on how many phases are in use.
current (droop)
ISEN
FB
resistor to develop the I
DS(ON)
ISEN
current provides information to perform the
CURRENT
R
TO OVER
FB
REFERENCE
AMPLIFIER
FIGURE 7. SIMPLIFIED FUNCTIONAL BLOCK DIAGRAM SHOWING CURRENT AND VOLTAGE SAMPLING
(Q2) x inductor current (I
is I
ERROR
TRIP
L
DAC
R
L
currents in multiple channels
IN
x r
+
-
COMPARATOR
C
DS(ON)
c
CHANNELS
TO OTHER
COMP
12
GENERATOR
ISEN
(Q2)/R
SAWTOOTH
+
ISEN
CORRECTION
-
+
current to the ISL6552
ISEN
DIFFERENCE
-
ISEN
L
). Note that I
REFERENCE
resistor is
.
-
+
AVERAGING
COMPARATOR
L
+
, the
ISL6552
-
ISL6552
CURRENT
SENSING
CURRENT
SENSING
FROM
OTHER
CHANNELS
CIRCUIT
PWM
The nominal current through the R
50µA at full output load current, and the nominal trip point for
over-current detection is 165% of that value, or 82.5µA.
Therefore, R
For a full load of 25A per phase, and an r
4mΩ, 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
With a high dv/dt load transient, typical of high performance
microprocessors, the largest deviations in output voltage occur
at the leading and trailing edges of the load transient. In order to
fully utilize the output-voltage tolerance range, the output
voltage is positioned in the upper half of the range when the
output is unloaded and in the lower half of the range when the
PWM
ISEN
ISEN
ISEN
= 2kΩ.
CORE
ONLY ONE OUTPUT
HIP6601
ISEN
= I
within limits under transient conditions.
STAGE SHOWN
L
R
x r
ISEN
value can be adjusted to change the
CORE
CURRENT(S)
DS(ON)
IN
CHANNELS
INDUCTOR
Q2
V
IN
OTHER
FROM
voltage with increasing load
Q1
(Q2)/50µA.
ISEN
PHASE
L
I
01
L
IN
resistor should be
IN
. This drop
DS(ON)
CORE
, so the average
V
to maintain
CORE
(Q2) of
ISEN