QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 835
LTC4441, MOSFET DRIVER
LTC4441
DESCRIPTION
Demonstration circuit DC835 is a MOSFET driver circuit
that is designed to facilitate adding a MOSFET driver to
an existing design.
Demonstration circuit DC835 is small and allows the
MOSFET driver LTC4441 to be added to an existing de-
sign in order to evaluate the performance. The board has
a ground strip along one side that can be directly sol-
dered to source pins of an SO-8 or similar MOSFET. This
assures the MOSFET driver will be most effective due to
low connection inductance between it’s output and
MOSFET gate pin.
Demonstration circuit DC835 can be easily modified to
generate different gate drive output voltages by chang-
ing the voltage divider of the internal LDO regulator.
The DC835 has a small circuit footprint. It is a high per-
formance and cost effective solution for driving big
MOSFETs in Telecom, Automotive and Industrial applica-
tions.
Design files for this circuit board are available. Call
the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
QUICK START PROCEDURE
Demonstration circuit DC835 is easy to set up to evalu-
ate the performance of the LTC4441. For proper meas-
urement equipment setup refer to Figure 1 and follow
the procedure below:
NOTE:
When
the power dissipation may overheat the part. Please
consult the LTC4441 data sheet for details.
3.
4.
Set the Pulse Generator to 300kHz and turn the pulse
output ON.
Check for the proper output voltage of 6V and wave-
forms as shown in Figure 3.
measuring the input or output voltage wave-
forms, care must be taken to minimize the length of the
oscilloscope probe ground lead. Measure the input or
output voltage waveforms by connecting the probe tip
directly across the PWM INPUT or G1 output and GND
terminals as shown in Figure 2.
With power off, connect the input power supply to Vin
and GND.
Turn the input power source on and slowly increase
the input voltage. Be careful not to exceed 24V.
NOTE:
PROGRAMMING GATE OUTPUT VOLTAGE
Changing resistor R8 can program the output voltage at
the OUT pin of the LTC4441. Do not change the value of
resistor R2. The 330kohm value is required for stability
of the internal LDO regulator. For more information,
please refer to the LTC4441 data sheet.
1.
2.
Higher input voltage will cause higher power
dissipation in the LTC4441 LDO regulator. If very big
MOSFETs are used and switching frequency is high
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 835
LTC4441, MOSFET DRIVER
ing circuit that may be used to circumvent the shortcom-
ings of other PWM circuit’s leading edge blanking.
Please refer to the LTC4441 data sheet for more details.
Demo Circuit DC835 has an input filter (R6 and C3) that
is used to prevent ringing on the PWM INPUT line from
causing false pulses at the output. This RC filter also
adds to the delay and needs to be taken into account.
The RC filter can be removed if the PWM input line is
laid out correctly and is relatively short.
BEWARE OF MOSFET DRIVER DELAYS
MOSFET driver delays, which are on the order of 30ns,
need careful consideration. Some PWM controllers have
built in leading edge blanking that prevents miss-
triggering of the current comparator due to leading edge
current spikes. If this blanking period is too short it may
not cover the additional delay caused by the MOSFET
driver. The LTC4441 has a built in programmable blank-
2
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