FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
GATE DRIVE CIRCUITS
LOW VOLTAGE RESET FUNCTION
The gate drive outputs (GDH1, GDH2, etc.) supply the
peak currents required to turn ON and hold ON the
MOSFETs, as well as turn OFF and hold OFF the MOSFETs.
When the logic supply voltage (VDD) drops below the
minimum voltage level or when the part is initially powered
up, this function will turn OFF and hold OFF the external
MOSFETs until the voltage increases above the minimum
voltage level required for normal operation.
CHARGE PUMP
The current capability of the charge pump is sufficient to
supply the gate drive circuit’s demands when PWMing at up
to 28 kHz. Two external charge pump capacitors and a
reservoir capacitor are required to complete the charge
pump’s circuitry.
CONTROL LOGIC
The control logic block controls when the low-side and
high-side drivers are enabled. The logic implements the Truth
Table found in the specification and monitors the M0, M1,
PWM, CL, OT, OV, LSE, and HSE pins. Note that the drivers
are enabled 3 µs after the PWM edge. During complimentary
chop mode the high-side and low-side drives are alternatively
enabled and disabled during the PWM cycle. To prevent
shoot-through current, the high-side drive turn-on is delayed
by tD1, and the low-side drive turn on is delayed by tD2 (see
Figure 4, page 8).
Charge reservoir capacitance is a function of the total
MOSFET gate charge (QG) gate drive voltage level relative to
the source (VGS) and the allowable sag of the drive level
during the turn-on interval (VSAG). CRES can be expressed by
the following formula:
QG x VGS
CRES
=
2
2 x VGS x VSAG - VSAG
Note that the drivers are disabled during an
overtemperature or overvoltage fault. A flip-flop keeps the
drive off until the following PWM cycle. This prevents erratic
operation during fault conditions. The current limit circuit also
uses a flip-flop for latching the drive off until the following
PWM cycle.
For example, for QG = 60 nC, VGS = 14 V, VSAG = 0.2 V:
(60 nC) x (14 V)
CRES
=
= 0.15 µF
2 x (14 V) x (0.2 V) - (0.2)2
Note PWM must be toggled after POR, Thermal Limit, or
overvoltage faults to re-enable the gate drivers.
Proper charge pump capacitance is required to maintain,
and provide for, adequate gate drive during high demand
turn-ON intervals. Use the following formula to determine
VGDH
values for CP1 and CP2
For example, for the above determination of CRES
0.15 µF:
:
The VGDH pin is used to provide a gate drive signal to a
reverse battery protection MOSFET. If reverse battery
protection is desired, VIGN would be applied to the source of
an external MOSFET, and the drain of the MOSFET would
then deliver a "protected" supply voltage (VIGNP) to the three
phase array of external MOSFETs as well as the supply
voltage to the VIGNP pin of the IC.
=
CRES
20
CRES
10
< CP1 = CP2
<
By averaging these two values, the proper CP value can
n
In a reverse polarity event (e.g., an erroneous installation
of the system battery), the VGDH signal will not be supplied to
the external protection MOSFET, and the MOSFET will
remain off and thus prevent reverse polarity from being
applied to the load and the VIGNP supply pin of the IC.
be determined:
0.15 µF
0.15 µF
= .015 µF, upper lim
= 0.075 µF, lower limit; and
20
10
CP1 and CP2 =(0.0075 µF + 0.015 µF) ÷ 2 = 0.01 µF
HIGH-SIDE GATE DRIVE CIRCUITS
THERMAL SHUTDOWN FUNCTION
Outputs GDH1, GDH2, and GDH3 provide the elevated
drive voltage to the high-side external MOSFETs (HS1, HS2,
and HS3; see Figure 5, page 13). These gate drive outputs
supply the peak currents required to turn ON and hold ON the
high-side MOSFETs, as well as turn OFF the MOSFETs.
These gate drive circuits are powered from an internal charge
pump, and therefore compensate for voltage dropped across
the load that is reflected to the source-gate circuits of the
high-side MOSFETs.
The device has internal temperature sensing circuitry
which activates a protective shutdown function should the die
reach excessively elevated temperatures. This function
effectively limits power dissipation and thus protects the
device.
OVERVOLTAGE SHUTDOWN FUNCTION
When the supply voltage (VIGN) exceeds the specified
over- voltage shutdown level, the part will automatically shut
down to protect both internal circuits as well as the load.
Operation will resume upon return of VIGN to normal
operating levels.
LOW-SIDE GATE DRIVE CIRCUITS
Outputs GDL1, GDL2, and GDL3 provide the drive voltage
to the low-side external MOSFETs (LS1, LS2, and LS3; see
33395
Analog Integrated Circuit Device Data
Freescale Semiconductor
10
