MCP8026 datasheet(33/64 Pages) MICROCHIP

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 2016 Microchip Technology Inc.

DS20005339B-page 33

MCP8025/6

4.3.4

EXTERNAL DRIVE FOR A 3-PHASE

BRIDGE WITH NMOS/NMOS

MOSFET PAIRS

Each

motor

phase

driven

with

external

NMOS/NMOS MOSFET pairs. These are controlled by

a low-side and a high-side gate driver. The gate drivers

are controlled directly by the digital input pins

PWM[1:3]H/L. A logic high turns the associated gate

driver ON and a logic low turns the associated gate

driver OFF. The PWM[1:3]H/L digital inputs are

equipped with internal pull-down resistors.

The low-side gate drivers are biased by the +12V LDO

output, referenced to ground. The high-side gate

drivers are a floating drive biased by a bootstrap

capacitor circuit. The bootstrap capacitor is charged by

the +12V LDO whenever the accompanying low-side

MOSFET is turned on.

The high-side and low-side driver outputs all go to a low

state whenever there is a fault or when CE = 0,

regardless of the PWM[1:3]H/L inputs.

4.3.4.1

MOSFET Driver External Protection

Features

Each driver is equipped with Undervoltage Lockout

(UVLO) and short-circuit protection features.

4.3.4.1.1 MOSFET Driver Undervoltage Lockout

(UVLO)

The MOSFET UVLO fault detection monitors the

available voltage used to drive the external MOSFET

gates. The fault detection is only active while the driver

is actively driving the external MOSFET gate. Anytime

the driver bias voltage is below the Driver Undervoltage

Lockout (DUVLO) threshold for a period longer than the

one specified by the tDUVLO parameter, the driver will

not turn on when commanded ON. A driver fault will be

indicated

the

host

microcontroller

the

ILIMIT_OUT open-drain output pin and also via a DE2

communication STATUS_1 message. This is a latched

fault. Clearing the fault requires either removal of

device power or disabling and re-enabling the device

via the device enable input (CE). The EXTUVLO bit in

the CFG0 register is used to enable or disable the

Driver Undervoltage Lockout feature. This protection

feature prevents the external MOSFETs from being

controlled with a gate voltage not suitable to fully

enhance the device.

4.3.4.1.2 External MOSFET Short-Circuit Current

Short-circuit protection monitors the voltage across the

external MOSFETs during an ON condition. The

high-side driver voltage is measured from VDD to

PH[1:3]. The low-side driver voltage is measured from

PH[1:3] to PGND. If the voltage rises above a

user-configurable threshold after the external MOSFET

gate voltage has been driven high, all drivers will be

turned OFF. A driver fault will be indicated to the host

microcontroller on the open-drain ILIMIT_OUT output

pin and also via a DE2 communication STATUS_1

message. This is a latched fault. Clearing the fault

requires either removal of device power or disabling

and re-enabling the device via the device enable input

(CE). This protection feature helps detect internal

motor failures such as winding to case shorts.

The short-circuit voltage may be set via a DE2

SET_CFG_0

message. The EXTOC<1:0> bits in the

CFG0 register are used to select the voltage level for

the short-circuit comparison. If the voltage across the

MOSFET drain-source terminals exceeds the selected

voltage level when the MOSFET is active, a fault will be

triggered. The selectable voltage levels are 250 mV,

500 mV, 750 mV and 1000 mV. The EXTSC bit in the

CFG0 register is used to enable or disable the

MOSFET driver short-circuit detection.

4.3.4.1.3 Fault Pin Output (ILIMIT_OUT)

The dual-purpose ILIMIT_OUT pin is used as a fault

indicator and as an overcurrent indicator when used

with the internal DAC. The pin is capable of sinking a

minimum of 1 mA of current while maintaining less than

50 mV of voltage across the output. An external pull-up

resistor to the logic supply is required.

The open-drain ILIMIT_OUT pin transitions low when a

fault occurs. Table 4-4 lists the faults that activate the

ILIMIT_OUT signal. Warnings do not activate the

ILIMIT_OUT signal. Table 4-5 lists the warnings.

Note:

The driver short-circuit protection is

dependent on application parameters. A

configuration message is provided for a

set number of threshold levels. The

MOSFET Driver UVLO and short-circuit

protection features have the option to be

disabled.

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