ISL6236AIRZ-T Intersil, ISL6236AIRZ-T Datasheet - Page 20

• Manufacturer Part Number: ISL6236AIRZ-T
• Description: IC MAIN PWR CTRLR QUAD 32-QFN
• Manufacturer: Intersil

Specifications of ISL6236AIRZ-T

• Applications: Controller, Notebook Computers
• Voltage - Input: 4.5 ~ 25 V
• Number Of Outputs: 4
• Operating Temperature: -40°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 32-VQFN Exposed Pad, 32-HVQFN, 32-SQFN, 32-DHVQFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -

addition, SMPS2 can also use REFIN2 to track its output from
0.5V to 2.50V. The ISL6236A contains fault-protection circuits
that monitor the main PWM outputs for undervoltage and
overvoltage conditions. A power-on sequence block controls
the power-up timing of the main PWMs and monitors the
outputs for undervoltage faults. The ISL6236A includes an
adjustable low drop-out linear regulator. The bias generator
blocks include the linear regulator, 3.3V precision reference, 2V
precision reference and automatic bootstrap switchover circuit.
The synchronous-switch gate drivers are directly powered
from PVCC, while the high-side switch gate drivers are
indirectly powered from PVCC through an external capacitor
and an internal Schottky diode boost circuit.
An automatic bootstrap circuit turns off the LDO linear
regulator and powers the device from BYP if LDOREFIN is
set to GND or VCC. See Table 1.
FREE-RUNNING, CONSTANT ON-TIME PWM
CONTROLLER WITH INPUT FEED-FORWARD
The constant on-time PWM control architecture is a
pseudo-fixed-frequency, constant on-time, current-mode
type with voltage feed forward. The constant on-time PWM
control architecture relies on the output ripple voltage to
provide the PWM ramp signal; thus the output filter
capacitor's ESR acts as a current-feedback resistor. The
high-side switch on-time is determined by a one-shot whose
period is inversely proportional to input voltage and directly
proportional to output voltage. Another one-shot sets a
minimum off-time (300ns typ). The on-time one-shot triggers
when the following conditions are met: the error comparator's
output is high, the synchronous rectifier current is below the
current-limit threshold, and the minimum off time one-shot
has timed out. The controller utilizes the valley point of the
output ripple to regulate and determine the off-time.
ON-TIME ONE-SHOT (t
Each PWM core includes a one-shot that sets the high-side
switch on-time for each controller. Each fast, low-jitter,
adjustable one-shot includes circuitry that varies the on-time
in response to battery and output voltage. The high-side
switch on-time is inversely proportional to the battery voltage
VOLTAGE at BYP
VOLTAGE at BYP
5V
3.3V
2 x LDOREFIN
LDO VOLTAGE
TABLE 1. LDO OUTPUT VOLTAGE TABLE
LDOREFIN < 0.3V,
BYP > 4.63V
LDOREFIN > VCC - 1V,
BYP > 3V
LDOREFIN < 0.3V,
BYP < 4.63V
LDOREFIN > VCC - 1V,
BYP < 3V
0.35V < LDOREFIN < 2.25V
ON
CONDITIONS
)
20
Internal LDO is
disabled.
Internal LDO is
disabled.
Internal LDO is
active.
Internal LDO is
active.
Internal LDO is
active.
COMMENT
ISL6236A
as measured by the VIN input and proportional to the output
voltage. This algorithm results in a nearly constant switching
frequency despite the lack of a fixed-frequency clock
generator. The benefit of a constant switching frequency is
that the frequency can be selected to avoid noise-sensitive
frequency regions, as shown in Equation 1:
See Table 2 for approximate K- factors. Switching frequency
increases as a function of load current due to the increasing
drop across the synchronous rectifier, which causes a faster
inductor-current discharge ramp. On-times translate only
roughly to switching frequencies. The on-times established
in the “Electrical Specifications” table on page 4 are
influenced by switching delays in the external high-side
power MOSFET. Also, the dead-time effect increases the
effective on-time, reducing the switching frequency. It occurs
only in PWM mode (SKIP = VCC) and during dynamic output
voltage transitions when the inductor current reverses at
light or negative load currents. With reversed inductor
current, the inductor's EMF causes PHASE to go high earlier
than normal, extending the on-time by a period equal to the
UGATE-rising dead time.
For loads above the critical conduction point, the actual
switching frequency is:
where:
• V
• V
• t
(t
or OPEN), VOUT1
(t
VOUT2
(t
VOUT1
(t
or OPEN), VOUT2
t
f
ON
ON
ON
ON
ON
inductor discharge path, including synchronous rectifier,
inductor and PC board resistances
charging path, including high-side switch, inductor and PC
board resistances
=
ON
DROP1
DROP2
------------------------------------------------------ -
t
=
= GND, REF,
= GND),
= VCC),
= VCC, REF,
ON
SMPS
V
is the on-time calculated by the ISL6236A
K V
--------------------------------------------------------------------------------------------------------- -
TABLE 2. APPROXIMATE K-FACTOR ERRORS
OUT
(
(
V
IN
OUT
is the sum of the parasitic voltage drops in the
is the sum of the parasitic voltage drops in the
+
+
V
V
DROP1
+
DROP2
I
LOAD
FREQUENCY
SWITCHING
)
(kHz)
⋅
V
400
500
200
300
r
IN
DS ON
(
) LOWERQ
(
K-FACTOR
(µs)
2.5
2.0
5.0
3.3
)
)
APPROXIMATE
ERROR (%)
K-FACTOR
March 18, 2008
±10
±10
±10
±10
(EQ. 1)
FN6453.3
(EQ. 2)