LM5035CEVAL/NOPB National Semiconductor, LM5035CEVAL/NOPB Datasheet - Page 3

• Manufacturer Part Number: LM5035CEVAL/NOPB
• Description: EVAL BOARD FOR LM5035C
• Manufacturer: National Semiconductor

Specifications of LM5035CEVAL/NOPB

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

A quick efficiency check is the best way to confirm that ev-
erything is operating properly. If something is amiss you can
be reasonably sure that it will affect the efficiency adversely.
Few parameters can be incorrect in a switching power supply
without creating losses and potentially damaging heat.
Over Current Protection
The evaluation board is configured with hiccup over-current
protection. In the event of an output overload (approximately
Digital Isolator
There is a total of four crossing of the isolation boundary; the
power transformer, the feedback and control of the two syn-
chronous MOSFETs. Usually an opto-coupler is used for
isolation of the feedback signal since this a relatively slow
analog signal. Most opto-couplers are too slow to use for the
synchronous MOSFET gate drive. There are fast opto-cou-
plers available but there is a big cost premium. Historically,
the most common approach has been to use gate drive trans-
formers to provide isolation for the synchronous gate drive
signals. The transformers can be used to directly drive the
MOSFET gates or the transformers can be used to just isolate
the control signal which is then applied to a gate driver IC on
the secondary side. Gate drive transformers have their chal-
lenges and limitations. Transformers cannot pass DC. A given
size transformer can only pass a finite voltage & time product
across the isolation boundary. After each on-time, the trans-
Typical Evaluation Setup
3
35A) the unit will discharge the softstart capacitor, which dis-
ables the power stage. After a delay the softstart is released.
The shutdown, delay and slow recharge time of the softstart
capacitor protects the unit, especially during short circuit
event where the stress is highest.
former needs to be reset, which imposes duty cycle limita-
tions. Further, during a sudden switch-off of the power
converter, the DC restorer capacitor on the secondary of the
gate drive transformer does not have a quick discharge path.
This will keep SR FET's turned on, resulting in a non-mono-
tonic decay of the output voltage.
These limitations can be addressed using a digital isolator.
The digital isolators are CMOS devices that use an RF cou-
pler to transmit digital information across the isolation barrier.
The isolation capability is up to 2500 VRMS. In simple words,
the digital isolators are similar to an opto-coupler. While, the
opto-couplers modulate light to transmit electrical signals, the
digital isolators modulate an RF signal across a semiconduc-
tor barrier. Furthermore, the digital isolators have lower prop-
agation delay than the gate drive transformers and do not
suffer volt-second limitations.
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