NCV7707, NCV7707B
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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),
the device returns to the Standby mode after an internal
delay of max. 8 ms, clearing all register content and setting
all output stages into high impedance state.