NCV7705 datasheet(21/38 Pages) ONSEMI

21 / 38 page

NCV7705(A), NCV7706

www.onsemi.com

Diagnostic Functions

All diagnostic functions (overcurrent, underload, power

supply monitoring, thermal warning and thermal shutdown)

are internally filtered. The failure condition has to be valid

for the minimum specified filtering time (td_old, td_uld,

td_uvov and td_tx) before the corresponding status bit in the

status register is set. The filter function is used to improve

the noise immunity of the device. The undercurrent and

temperature warning functions are intended for information

purpose and do not affect the state of the output drivers. An

overcurrent condition disables the corresponding output

driver while a thermal shutdown event disables all outputs

into high impedance state. Depending on the setting of the

overcurrent recovery bits in the input register, the driver can

either perform an auto−retry or remain latched off until the

microcontroller clears the corresponding status bits.

Overtemperature shutdown is latch−off only, without

auto−retry functionality.

Overvoltage / Undervoltage Shutdown

If the supply voltage Vs rises above the switch off voltage

Vov_vs(off) or falls below Vuv_vs(off), all output

transistors are switched to high−impedance state and the

global status bit UOV_OC (multi information) is set. The

status flag STATUS_2.VSOV, resp. STATUS_2.VSUV is

set, too, to log the over−/under−voltage event. The bit

CONTROL_3.OVUVR can be used to determine the

recovery behavior once the Vs supply voltage gets back into

the specified nominal operating range. OVUVR = 0 enables

auto−recovery, with OVUVR = 1 the output stages remain

in high impedance condition until the status flags have been

cleared. Once set, STATUS2.VSOV / VSUV can only be

reset by a read&clear access to the status register

STATUS_2.

Thermal Warning and Overtemperature Shutdown

The device provides a dual−stage overtemperature

protection. If the junction temperature rises above Tjtw_on,

a temperature warning flag (TW) is set in the Global Status

Byte and can be read via SPI. The control software can then

react onto this overload condition by a controlled disable of

individual outputs. If however the junction temperature

reaches the second threshold Tjsd_on, the thermal shutdown

bit TSD is set in the Global Status Byte and all output stages

are switched into high impedance state to protect the device.

The minimum shutdown delay for overtemperature is td_tx.

The output channels can be re−enabled after the device

cooled down and the TSD flag has been reset by the

microcontroller by setting CONTROL_0.MODE = 0.

Openload (Underload) Detection

The openload detection monitors the load current in the

output stage while the transistor is active. If the load current

is below the openload detection threshold for at least td_uld,

the corresponding bit (ULDx) is set in the status registers

STATUS_1/2. The status of the output remains unchanged.

Once set, ULDx remains set regardless of the actual load

condition. It has to be reset by a read&write access to the

corresponding status register.

Overload Detection

An overcurrent condition is indicated by the flag

(UOV_OC) in the Global Status Byte after a filter time of at

least td_old. The channel dependent overcurrent flags are set

in the status registers (STATUS_0/2.OCx) and the

corresponding driver is switched into high impedance state

to protect the device. Each low−side and high−side driver

stage provides its own overcurrent flag. Resetting this

overcurrent flag automatically re−enables the respective

output (provided it is still enabled thru the Control register).

If the over current recovery function is enabled, the internal

chip logic automatically resets the overcurrent flag after a

fixed delay time, generating a PWM modulated current with

a programmable duty cycle. Otherwise the status bits have

to be cleared by the microcontroller by a read&clear access

to the corresponding status register.

Cross−current Protection

All six half−bridges are protected against cross−currents

by internal circuitry. If one driver is turned off (LS or HS),

the activation of the other driver of the same output will be

automatically delayed by the cross current protection

mechanism until the active driver is safely turned off.

Mode Control

Wake−up and Mode Control

Two different modes are available:

• Active mode

• Standby mode

After power−up of VCC the device starts in Standby

mode. Pulling the chip−select signal CSB to low level causes

the device to change into Active mode (analog part active).

After at least 10

ms delay, the first SPI communication is

valid and bit CONTROL_0.MODE can be used to set the

desired mode of operation. If bit MODE remains reset (0) or

CSB remains low longer than tcsb_low_stdby, the device

returns to the Standby mode after an internal delay of max.

ms, clearing all register content and setting all output stages

into high impedance state.

NCV7705 Datasheet(PDF) 21 Page - ON Semiconductor

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