MAX5078
4A, 20ns, MOSFET Driver
8
Maxim Integrated
Detailed Description
V
DD
Undervoltage Lockout (UVLO)
The MAX5078A/MAX5078B have internal undervoltage
lockout (UVLO) for V
DD
. When V
DD
is below the UVLO
threshold, OUT is pulled low independent of the state of
the inputs. The undervoltage lockout is typically 3.5V with
200mV typical hysteresis to avoid chattering. When V
DD
rises above the UVLO threshold, the output goes high or
low depending upon the logic-input levels. Bypass V
DD
using a low-ESR ceramic capacitor for proper operation
(see the
Applications Information
section).
Logic Inputs
The MAX5078A has CMOS logic inputs while the
MAX5078B has TTL-compatible logic inputs. The logic
inputs are protected against the voltage spikes up to
18V, regardless of the V
DD
voltage. The TTL and CMOS
logic inputs have 300mV and 0.1 x V
DD
hysteresis,
respectively, to avoid double pulsing during transition.
The low 2.5pF input capacitance reduces loading and
increases switching speed.
The logic inputs are high impedance and must not be left
floating. If the inputs are left open, OUT can go to an
undefined state as soon as V
DD
rises above the UVLO
threshold. Therefore, the PWM output from the controller
must assume proper state when powering up the device.
The MAX5078A/MAX5078B have two logic inputs, provid-
ing greater flexibility in controlling the MOSFET. Use IN+
for noninverting logic and IN- for inverting logic operation.
Connect IN+ to V
DD
and IN- to GND, if not used.
Alternatively, the unused input can be used as an
ON/OFF function. Use IN+ for active-low shutdown logic
and IN- for active-high shutdown logic (see Figure 3). See
Table 1 for all possible input combinations.
Driver Output
The MAX5078A/MAX5078B have low R
DS(ON)
p-channel
and n-channel devices (totem pole) in the output stage
for the fast turn-on/turn-off, high-gate-charge switching
MOSFETs. The peak source or sink current is typically
4A. The output voltage (V
OUT
) is approximately equal to
V
DD
when in high state and is ground when in low state.
The driver R
DS(ON)
is lower at higher V
DD
resulting in
higher source-/sink-current capability and faster switch-
ing speeds. The propagation delays from the noninvert-
ing and inverting logic inputs to OUT are matched to 2ns
typically. The break-before-make logic avoids any cross-
conduction between the internal p- and n-channel
devices, and eliminates shoot-through, thus reducing the
quiescent supply current.
Applications Information
RLC Series Circuit
The driver’s R
DS(ON)
(R
ON
), internal bond/lead induc-
tance (L
P
), trace inductance (L
S
), gate inductance (L
G
),
and gate capacitance (C
G
) form a series RLC
circuit with a second-order characteristic equation. The
series RLC circuit has an undamped natural frequency
(ϖ
0
) and a damping ratio (ζ) where:
The damping ratio needs to be greater than 0.5 (ideally
1) to avoid ringing. Add a small resistor (R
GATE
) in
series with the gate when driving a very low gate-
charge MOSFET, or when the driver is placed away
from the MOSFET.
Power Supply. Bypass to GND with one or more 0.1µF ceramic capacitors.
when not used.
Exposed Pad. Internally connected to GND. Do not use the exposed pad as the only electrical
ground connection.
