MIC4607 Datasheet, PDF (21/42 Pages) Microchip Technology – 85V, Three-Phase MOSFET Driver with Adaptive Dead-Time, Anti-Shoot-Through and Overcurrent Protection

the forward voltage drop of the internal diode). After the
low-side MOSFET is turned off and the AHO pin turns
on, the voltage across capacitor C_B is applied to the
gate of the high-side external MOSFET. As the
high-side MOSFET turns on, voltage on the AHS pin
rises with the source of the high-side MOSFET until it
reaches V_IN. As the AHS and AHB pins rise, the inter-
nal diode is reverse biased, preventing capacitor C_B
from discharging. During this time, the high-side MOS-
FET is kept ON by the voltage across capacitor C_B.
FIGURE 5-3:
Example.
MIC4607 Motor Driver
5.6 Programmable Gate Drive
The MIC4607 offers programmable gate drive,
meaning the MOSFET gate drive (gate-to-source
voltage) equals the V_DD voltage. This feature offers
designers flexibility in selecting the proper MOSFETs
for a given application. Different MOSFETs require
different V_GS characteristics for optimum R_DSON
performance. Typically, the higher the gate voltage (up
to 16V), the lower the R_DSON achieved. For example,
as shown in Figure 5-4, a NTMSF4899NF MOSFET
can be driven to the ON state with a gate voltage of
5.5V but R_DSON is 5.2 mΩ. If driven to 10V, R_DSON is
4.1 mΩ – a decrease of 20%.
In low-current applications, the losses due to R_DSON
are minimal, but in high-current motor drive applica-
tions such as power tools, the difference in R_DSON can
lower the efficiency, reducing run time.
MIC4607
5.7 Overcurrent Protection Circuitry
The MIC4607 provides overcurrent protection for the
motor driver circuitry. It consists of:
• A comparator that senses the voltage across a
current-sense resistor
• A latch and timer that keep all gate drivers off
during a fault
• An open-drain pin that pulls low during the fault.
If an overcurrent condition is detected, the FLT/ pin is
pulled low and the gate drive outputs are latched off for
a time that is determined by the DLY pin circuitry. After
the delay circuitry times out, a high-going edge on any
of the LI pins (for the MIC4607-1 version) or a low-going
edge on any of the PWM pins (for the MIC4607-2
version) is required to reset the latch, de-assert the FLT/
pin and allow the gate drive outputs to switch.
For additional information, refer to the Timing Diagrams
section as well as the Functional Diagram section.
5.7.1 ILIM
The ILIM+ and ILIM- pins provide a Kelvin-sensed cir-
cuit that monitors the voltage across an external cur-
rent sense resistor. This resistor is typically connected
between the source pins of all three low-side MOSFETs
and power ground. If the peak voltage across this resis-
tor exceeds the VI_LIM+ threshold, it will cause all six out-
puts to latch off. Both pins should be shorted to V_SS
ground if the overcurrent features is not used.
5.7.2 DLY
A capacitor connected to the DLY pin determines the
amount of time the gate drive outputs are latched off
before they can be restarted.
During normal operation, the DLY pin is held low by an
internal MOSFET. After an over-current condition is
detected, the MOSFET turns off and the external
capacitor is charged up by an internal current source.
The outputs remain latched off until the DLY pin voltage
reaches the V_DLY+ threshold (typically 1.5V).
The delay time can be approximately calculated using
Equation 5-1.
EQUATION 5-1:
t_DLY
=
C_{-----D----L---Y----}_-----V_{-----D----L---Y----}
I _DLY
FIGURE 5-4:
MOSFET R_DSON vs. V_GS.
 2016 Microchip Technology Inc.
DS20005610A-page 21