Dual High-Speed 1.5A MOSFET Drivers
Applications Information
The MAX4426/MAX4427/MAX4428 have easy-to-drive
inputs. However, these inputs must never be allowed to
stay between VIH and VIL for more than 50ns. Unused
inputs should always be connected to ground to mini-
mize supply current. Drivers can be paralleled on the
MAX4426 or MAX4427 by tying both Inputs together and
both outputs together.
Supply bypassing and grounding are extremely impor-
tant with the MAX4426/MAX4427/MAX4428, as the peak
supply current can be as high as 3A, which is twice the
peak output current. Ground drops are a form of nega-
tive feedback with inverters, and hence will degrade the
delay and transition time of the MAX4426/MAX4428.
Suggested bypass capacitors are a 4.7µF (low ESR)
capacitor in parallel with a 0.1µF ceramic capaci-
tor, mounted as close as possible to the MAX4426/
MAX4427/MAX4428. Use a ground plane if possible or
separate ground returns for inputs and outputs. Output
voltage ringing can be minimized with a 5Ω to 20Ω resis-
tor in series with the output, but this will degrade output
transition time. Ringing may be undesirable due to the
large current that flows through capacitive loads when
the voltage across these loads transitions quickly.
Operation at the upper end of the supply voltage range
(> 15V) requires that a capacitance of at least 50pF be
present at the outputs. This prevents the supply voltage
provided to the die (which can be different from that
seen at the supply pin) from exceeding the 20V absolute
maximum rating, due to overshoot. Since at least 50pF
of gate capacitance is present in all higher power FETs,
this requirement is easily met.
Power Dissipation
The MAX4426/MAX4427/MAX4428 power dissipation
consists of input inverter losses, crowbar current through
the output devices, and output current (either capacitive
or resistive). The sum of these must be kept below the
maximum power dissipation limit.
The DC input inverter supply current is 0.2mA when both
inputs are low and 2mA when both inputs are high. The
crowbar current through an output device making a tran-
sition is approximately 100mA for a few nanoseconds.
This is a small portion of the total supply current, except
for high switching frequencies or a small load capaci-
tance (100pF).
The MAX4426/MAX4427/MAX4428 power dissipation
when driving a ground-referenced resistive load is:
P = (D) (rON(MAX)) (ILOAD2)
where D is the percentage of time the MAX4426/
MAX4427/MAX4428 output pulls high, rON(MAX)
is the MAX4426/MAX4427/MAX4428 maximum on
resistance, and ILOAD is the MAX4426/MAX4427/
MAX4428 load current.
For capacitive loads. the power dissipation is:
P = (CLOAD) (VDD2) (FREQ)
where CLOAD is the capacitive load. VDD is the MAX4426/
MAX4427/MAX4428 supply voltage, and FREQ is the
toggle frequency.