MIC4607 Datasheet, PDF (24/42 Pages) Microchip Technology – 85V, Three-Phase MOSFET Driver with Adaptive Dead-Time, Anti-Shoot-Through and Overcurrent Protection

MIC4607
turn-off. The xLO driver turns on after a short delay
(t_LOON). Once the xLO driver is turned on, it is latched
on until the xPWM signal goes high. This prevents any
ringing or oscillations on the switch node or xHS pin
from turning off the xLO driver. If the xPWM pin goes
low and the voltage on the xHS pin does not cross the
V_SWTH threshold, the xLO pin will be forced high after
a short delay (t_SWTO), ensuring proper operation.
The internal logic circuits also ensure a “first on” priority
at the inputs. If the xHO output is high, the xLI pin is
inhibited. A high signal or noise glitch on the xLI pin has
no effect on the xHO or xLO outputs until the xHI pin
goes low. Similarly, xLO being high holds xHO low until
xLI and xLO are low.
Fast propagation delay between the input and output
drive waveform is desirable. It improves overcurrent
protection by decreasing the response time between
the control signal and the MOSFET gate drive. Minimiz-
ing propagation delay also minimizes phase shift errors
in power supplies with wide bandwidth control loops.
Care must be taken to ensure that the input signal
pulse width is greater than the minimum specified pulse
width. An input signal that is less than the minimum
pulse width can result in no output pulse or an output
pulse whose width is significantly less than the input.
The maximum duty cycle (ratio of high-side on-time to
switching period) is determined by the time required for
the C_B capacitor to charge during the off-time. Ade-
quate time must be allowed for the C_B capacitor to
charge up before the high-side driver is turned back on.
Although the adaptive dead-time circuit in the MIC4607
prevents the driver from turning both MOSFETs on at
the same time, other factors outside of the
anti-shoot-through circuit’s control can cause
shoot-through. Other factors include ringing on the gate
drive node and capacitive coupling of the switching
node voltage on the gate of the low-side MOSFET.
The scope photo in Figure 6-4 shows the dead time
(<20 ns) between the high- and low-side MOSFET
transitions as the low-side driver switches off while the
high-side driver transitions from off to on.
FIGURE 6-4:
Adaptive Dead-Time LO
(LOW) to HO (HIGH).
Table 6-1 contains truth tables for the MIC4607-1 (inde-
pendent TTL inputs) and Table 6-2 is for the
MIC4607-2 (PWM inputs) that details the “first on” pri-
ority as well as the failsafe delay (t_SWTO).
TABLE 6-1: MIC4607-1 TRUTH TABLE
xLI xHI xLO xHO
Comments
00
0
0 Both outputs off.
01
0
xHO will not go HIGH
1 until xLO falls below
1.9V.
10
1
xLO will be delayed an
0 extra 250 ns if xHS
never falls below 2.2V.
First ON stays on until
11
X
X input of same goes
LOW.
TABLE 6-2: MIC4607-2 TRUTH TABLE
xPWM xLO xHO
Comments
xLO will be delayed an
0
1
0 extra 250 ns if xHS
never falls below 2.2V.
xHO will not go HIGH
1
0
1 until xLO falls below
1.9V.
6.2 HS Node Clamp
A resistor/diode clamp between the switching node and
the HS pin is necessary to clamp large negative
glitches or pulses on the HS pin.
Figure 6-5 shows the Phase A section high-side and
low-side MOSFETs connected to one phase of the
three phase motor. There is a brief period of time (dead
time) between switching to prevent both MOSFETs
from being on at the same time. When the high-side
MOSFET is conducting during the on-time state, cur-
rent flows into the motor. After the high-side MOSFET
turns off, but before the low-side MOSFET turns on,
current from the motor flows through the body diode in
parallel with the low-side MOSFET. Depending upon
the turn-on time of the body diode, the motor current,
and circuit parasitics, the initial negative voltage on the
switch node can be several volts or more. The forward
voltage drop of the body diode can be several volts,
depending on the body diode characteristics and motor
current.
Even though the HS pin is rated for negative voltage, it
is good practice to clamp the negative voltage on the
HS pin with a resistor and possibly a diode to prevent
excessive negative voltage from damaging the driver.
Depending upon the application and amount of nega-
tive voltage on the switch node, a 3Ω resistor is recom-
DS20005610A-page 24
 2016 Microchip Technology Inc.