MCP8024 datasheet(22/46 Pages) MICROCHIP

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MCP8024

DS20005228A-page 22

 2013 Microchip Technology Inc.

4.2.3.1

External Driver Protection Features

Each driver is equipped with Undervoltage Lock Out

(UVLO) and short circuit protection features.

4.2.3.1.1 Driver Undervoltage Lock Out (UVLO)

At anytime the driver bias voltage is below the Driver

Undervoltage Lock Out threshold (DUVLO), 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

communications 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). Bit 3 of the

Configuration 0 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.

4.2.3.1.2 External MOSFET Short Circuit Current

Short circuit protection monitors the voltage across the

external MOSFETs during an ON condition. If the volt-

age rises above a user configurable threshold, all driv-

ers will be turned OFF. A driver fault will be indicated

to the host microcontroller on the open-drain ILIM-

IT_OUT output pin and also via a DE2 communica-

tions Status

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.

Note:

The

driver

short-circuit

protection

dependent on application parameters. A

configuration message is provided for a set

number of threshold levels. In addition,

Driver UVLO and/or short-circuit protection

has the option to be disabled.

The short-circuit voltage may be set via a DE2

Set_Cfg_0

message. Bits 0 and 1 are used to select the

voltage level for the short circuit comparison. If the

voltage across the MOSFET drain-source exceeds the

selected voltage level, a fault will be triggered. The

selectable voltage levels are 250 mV, 500 mV, 750 mV,

and 1000 mV. Bit 2 of the Configuration 0 register is

used to enable or disable the short-circuit detection.

4.2.3.2

Gate Control Logic

The gate control logic provides level shifting of the dig-

ital inputs, polarity control, and cross conduction pro-

tection. Cross conduction protection is performed in

two ways.

4.2.3.2.1 Cross Conduction Protection

First, logic prevents switching ON one power MOSFET

while the opposite one in the same half-bridge is

already switched ON. If both MOSFETs in the same

half-bridge are commanded on simultaneously by the

digital inputs, both will be turned OFF.

4.2.3.2.2 Programmable Dead Time

Second, the gate control logic employs a break-

before-make dead-time delay that is programmable. A

configuration message is provided to configure the

driver dead time. The allowable dead times are 250

ns, 500 ns, 1 µs and 2 µs.

4.2.3.2.3 Programmable Blanking Time

A configuration message is provided to configure the

driver current limit blanking time. The blanking time

allows the system to ignore any current spikes that

may occur when switching outputs. The allowable

blanking times are 500 ns, 1 µs, 2µs, and 4µs

(default). The blanking time will start after the dead

time circuitry has timed out.

4.3

CHIP ENABLE (CE)

The Chip Enable (CE) pin allows the device to be dis-

abled by external control. When the Chip Enable pin is

not active, the following subsystems are disabled:

• high side gate drives (HA, HB, HC)

• low side gate drives (LA, LB, LC)

• 12V LDO

• 30K pull-up resistor connected to the level trans-

lator is switched out of the circuit to minimize cur-

rent consumption (configurable).

The 5V LDO and Buck Regulator stay enabled. The

DE2 communications port remains active but the port

may only respond to commands. When CE is inactive,

the DE2 port is prevented from initiating communica-

tions in order to conserve power.

The total current consumption of the device when CE

is inactive (device disabled) stays within the “input qui-

escent current” limits specified in the device character-

istics table.

4.4

COMMUNICATION PORTS

The communication ports provide a means of commu-

nicating to the host system.

4.4.1

DE2 COMMUNICATIONS PORT

A half-duplex 9600 baud UART interface is available to

communicate with an external host. The port is used to

configure the MCP8024 and also for status and fault

messages.

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