33880_12 Datasheet, PDF (18/25 Pages) Freescale Semiconductor, Inc – Configurable Octal Serial Switch with Serial Peripheral Interface I/O

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
SHORTED LOAD FAULT
A shorted load (overcurrent) fault can be caused by any
output being shorted directly to supply or an output causing
the device to current limit (linear short).
There are two safety circuits progressively in operation
during load short conditions providing system protection:
1. The device’s output current is monitored in an analog
fashion using SENSEFET™ approach and current
limited.
2. The device’s output thermal limit is sensed and when
attained causes only the specific faulted output to shut
down. The output will remain off until cooled. The
device will then reassert the output automatically. The
cycle will continue until the fault is remove or the
command bit instructs the output off.
UNDERVOLTAGE SHUTDOWN
An undervoltage V_DD condition will result in the global
shutdown of all outputs. The undervoltage threshold is
between 3.9 V and 4.6 V. When V_DD goes below the
threshold, all outputs are turned OFF and the Fault Status
(FS) register is cleared. As V_DD returns to normal levels, the
FS register will resume normal operation.
An undervoltage condition at the VPWR pin will not cause
output shutdown and reset. When V_PWR is between 5.5 V
and 9.0 V, the output will operate per the command word.
However, the status as reported by the serial data output
(DO) pin may not be accurate below 9.0 V V_PWR. Proper
operation at V_PWR voltages below 5.5 V cannot be
guaranteed.
OUTPUT VOLTAGE CLAMP
Each output of the 33880 incorporates an internal voltage
clamp to provide fast turn-off and transient protection of each
output. Each clamp independently limits the drain-to-source
voltage to 45 V for low-side drive configurations and -20 V for
high-side drive configurations (see Figure 25). The total
energy clamped (E_J) can be calculated by multiplying the
current area under the current curve (I_A) times the clamp
voltage (V_CL).
Characterization of the output clamps, using a single pulse
non-repetitive method at 0.3 A, indicates the maximum
energy to be 50 mJ at 150°C junction temperature per output.
Drain-to-Source Clamp
Voltage (V_CL = 45 V)
Drain Voltage
Drain Current
(I_D = 0.3 A)
Clamp Energy
(E_J = I_A x V_CL)
Drain-to-Source ON
Voltage (V_DS(ON))
GND
V_BAT
Drain-to-Source ON
Voltage (V_DS(ON))
GND
Current
Area (I_A)
Current
Area (I_A)
Time
Time
Clamp Energy
(E_J = I_A x V_CL)
Source Current
(I_S = 0.3 A)
Source Clamp Voltage
(V_CL = -20 V)
Source Voltage
Figure 25. Output Voltage Clamping
SPI CONFIGURATIONS
The SPI configuration on the 33880 device is consistent
with other devices in the OSS family. This device may be
used in serial SPI or parallel SPI with the 33291 and 33298.
Different SPI configurations may be provided. For more
information, contact Analog Products Division.
REVERSE BATTERY
The 33880 has been designed with reverse battery
protection on the VPWR pin. However, the device does not
protect the load from reverse battery. During the reverse
battery condition, current will flow through the load via the
output MOSFET substrate diode. Under this circumstance
relays may energize and lamps will turn on. If load reverse
battery protection is desired, a diode must be placed in series
with the load.
33880
18
Analog Integrated Circuit Device Data
Freescale Semiconductor