ISL6537CR Intersil, ISL6537CR Datasheet - Page 10

• Manufacturer Part Number: ISL6537CR
• Description: IC REG/CTRLR ACPI DUAL DDR 28QFN
• Manufacturer: Intersil

Specifications of ISL6537CR

• Applications: Memory, DDR/DDR2 Regulator
• Current - Supply: 7mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 28-QFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Supply: -

will immediately shut down when the Fault Counter reaches
a count of 5 at any other time.
The 16384 counts that are required to reset the Fault Reset
Counter represent 8 soft-start cycles, as one soft-start cycle
is 2048 clock cycles. This allows the ISL6537 to attempt at
least one full soft-start sequence to restart the faulted
regulators.
When attempting to restart a faulted regulator, the ISL6537
will follow the preset start up sequencing. If a regulator is
already in regulation, then it will not be affected by the start
up sequencing.
V
The overcurrent function protects the switching converter from
a shorted output by using the upper MOSFET on-resistance,
r
converter’s efficiency and reduces cost by eliminating a
current sensing resistor.
The overcurrent function cycles the soft-start function in a
hiccup mode to provide fault protection. A resistor (R
programs the overcurrent trip level (see Typical Application
diagrams on pages 3 and 4). An internal 20μA (typical) current
sink develops a voltage across R
the converter input voltage. When the voltage across the
upper MOSFET (also referenced to the converter input
voltage) exceeds the voltage across R
function initiates a soft-start sequence. The initiation of soft-
start may affect other regulators. The V
directly affected as it receives it’s reference and input from
V
The overcurrent function will trip at a peak inductor current
(I
where I
typical). The OC trip point varies mainly due to the MOSFET
r
normal operating load range, find the R
the equation above with:
For an equation for the ripple current see the section under
component guidelines titled ‘Output Inductor Selection’.
A small ceramic capacitor should be placed in parallel with
R
presence of switching noise on the input voltage.
I
DS(ON)
DS(ON)
1. The maximum r
2. The minimum I
3. Determine I
PEAK
DDQ
PEAK)
OCSET
DDQ
temperature.
where ΔI is the output inductor ripple current.
.
=
Overcurrent Protection
OCSET
, to monitor the current. This method enhances the
determined by:
variations. To avoid overcurrent tripping in the
to smooth the voltage across R
I
---------------------------------------------------- -
OCSET
r
is the internal OCSET current source (20μA
DS ON
PEAK
x R
(
OCSET
DS(ON)
OCSET
)
for
I
PEAK
from the specification table.
at the highest junction
10
>
OCSET
I
OUT MAX
OCSET
TT_DDR
(
OCSET
that is referenced to
OCSET
)
, the overcurrent
+
(
--------- -
regulator is
ΔI
resistor from
2
in the
)
,
OCSET
(EQ. 3)
)
ISL6537
Thermal Protection (S0/S3 State)
If the ISL6537 IC junction temperature reaches a nominal
temperature of +140°C, all regulators will be disabled. The
ISL6537 will not re-enable the outputs until the junction
temperature drops below +110°C and either the bias voltage
is toggled in order to initiate a POR or the SLP_S5 signal is
forced LOW and then back to HIGH.
Shoot-Through Protection
A shoot-through condition occurs when both the upper and
lower MOSFETs are turned on simultaneously, effectively
shorting the input voltage to ground. To protect from a shoot-
through condition, the ISL6537 incorporates specialized
circuitry on the V
complementary MOSFETs are not ON simultaneously.
The adaptive shoot-through protection utilized by the V
regulator looks at the lower gate drive pin, LGATE, and the
upper gate drive pin, UGATE, to determine whether a
MOSFET is ON or OFF. If the voltage from UGATE or from
LGATE to GND is less than 0.8V, then the respective
MOSFET is defined as being OFF and the other MOSFET is
allowed to turned ON. This method allows the V
regulator to both source and sink current.
Since the voltage of the MOSFET gates are being measured
to determine the state of the MOSFET, the designer is
encouraged to consider the repercussions of introducing
external components between the gate drivers and their
respective MOSFET gates before actually implementing
such measures. Doing so may interfere with the shoot-
through protection.
Application Guidelines
Layout Considerations
Layout is very important in high frequency switching
converter design. With power devices switching efficiently at
250kHz, the resulting current transitions from one device to
another cause voltage spikes across the interconnecting
impedances and parasitic circuit elements. These voltage
spikes can degrade efficiency, radiate noise into the circuit,
and lead to device overvoltage stress. Careful component
layout and printed circuit board design minimizes these
voltage spikes.
As an example, consider the turn-off transition of the control
MOSFET. Prior to turn-off, the MOSFET is carrying the full
load current. During turn-off, current stops flowing in the
MOSFET and is picked up by the lower MOSFET. Any
parasitic inductance in the switched current path generates a
large voltage spike during the switching interval. Careful
component selection, tight layout of the critical components,
and short, wide traces minimizes the magnitude of voltage
spikes.
There are two sets of critical components in the ISL6537
switching converter. The switching components are the most
DDQ
regulator which insures that
DDQ
July 18, 2007
FN9142.6
DDQ