EL7571CMZ Intersil, EL7571CMZ Datasheet - Page 9

• Manufacturer Part Number: EL7571CMZ
• Description: IC CTRLR PWM PROGRAMMABLE 20SOIC
• Manufacturer: Intersil

Specifications of EL7571CMZ

• Applications: Controller, Intel Pentium® II, Pro
• Voltage - Input: 4.5 ~ 12.6 V
• Number Of Outputs: 2
• Voltage - Output: 1.3 ~ 3.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 20-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

where:
Since inductance value tends to decrease with current,
ripple current will generally be greater than 21
output current.
Once the minimum output inductance is determined, an off
the shelf inductor with current rating greater than the
maximum DC output required can be selected. Pulse
Engineering and Coil Craft are two manufactures of high
current inductors. For converter designers who want to
design their own high current inductors, for experimental
purposes or to further reduce costs, we recommend the
Micrometals Powered Iron Cores data sheet and
applications note as a good reference and starting point.
Current Sense Resistor, R
Inductor current is monitored indirectly via a low value
resistor R
resistor is used to set the maximum operating current, the
current reversal threshold and the system load regulation. To
ensure reliable system operation it is important to sense the
actual voltage drop across the resistor. Accordingly a four
wire Kelvin connection should be made to the controller
current sense inputs. There are two criteria for selecting the
resistor value and type. Firstly, the minimum value is limited
by the maximum output current. The EL7571 current limit
capacitor has a typical threshold of 154mV, 125mV
minimum. When the voltage across the sense resistor
exceeds this threshold, the conduction cycle of the top
switch terminates immediately, providing pulse by pulse
Bill of Materials
PCB Trace Resistor
I
T
V
F
V
I
MANUFACTURER
PEAK
MIN
ON
SW
OUT
IN
Mills Resistor
= input voltage
= top switch on time
= minimum load
= switching frequency
= output voltage
= peak ripple current
Dale
IRC
1
. The voltage developed across the current sense
MRS1367-TBA
OARS Series
PART NO.
WSL 2512
9
1
TOLERANCE
±10%
±30%
MIN
±1%
±5%
at higher
TEMPERATURE
EL7571
COEFFICIENT
±4000ppm
±75ppm
±20ppm
±20ppm
current limiting. A resistor value must be selected which
guarantees operation under maximum load. That is:
where:
Secondly, since the load current passes directly through the
sense resistor, its power rating must be sufficient to handle
the power dissipated during maximum load (current limit)
conditions. Thus:
where:
P
resistor. High current applications may require parallel sense
resistors to dissipate sufficient power. Current Sense
Resistor Table below lists some popular current sense
resistors: the WLS-2512 series of Power Metal Strip
Resistors from Dale Electronics, OARS series Iron Alloy
resistor from IRC, and Copper Magnanin (CuNi) wire resistor
from Mills Resistors. Mother board copper trace is not
recommended because of its high temperature coefficient
and low power dissipation. The trade-off between the
different types of resistors are cost, space, packaging and
performance. Although Power Metal Strip Resistors are
relatively expensive, they are available in surface mount
packaging with tighter tolerances. Consequently, less board
space is used to achieve a more accurate current sense.
Alternatively, Magnanin copper wire has looser tolerance
and higher parasitic inductance. This results in a less current
sense but at a much lower cost. Metal track on the PCB can
also be used as current sense resistor. The trade-offs are
±30% tolerance and ±4000 ppm temperature coefficient.
Ultimately, the selection of the type of current sense element
must be made on an application by application basis.
D
V
I
P
MAX
must be less than the power rating of the current sense
OCMIN
D
= power dissipated in current sense resistor
= maximum output current
POWER RATING
50A/in (1oz Cu)
= minimum over current voltage threshold
1W - 5W
1.2W
1W
P
D
R
=
1
1
OUTMAX
=
402-563-6506
800-472-6467
916-422-5461
PHONE NO.
V
---------------------- -
1
OCMIN
MAX
2
×
R
1
402-563-6418
800-472-3282
906-422-1409
FAX NO.