33984 Datasheet, PDF (20/38 Pages) Freescale Semiconductor, Inc – Dual Intelligent High-current Self-protected Silicon High Side Switch (4.0 mOhm)

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
The 33984 has four operating modes: Sleep, Normal,
Fault, and Fail-safe. Table 6 summarizes details contained in
succeeding paragraphs.
Table 6. Fail-safe Operation and Transitions to Other
33984 Modes
Mode FS WAKE RST WDTO
Comments
Sleep x
0
0
x ^{Device is in Sleep mode.}
All outputs are OFF.
Normal 1
x
1
No ^{Normal mode. Watchdog}
is active if enabled.
Fault 0
1
x
No The device is currently in
0
x
1
Fault mode. The faulted
output(s) is (are) OFF.
Fail- 1
0
1 Yes Watchdog has timed out
safe
1
1
1
and the device is in Fail-
safe mode. The outputs
1
1
0
are as configured with
the RFS resistor
connected to FSI. RST
and WAKE must be
transitioned to Logic [0]
simultaneously to bring
the device out of the Fail-
safe mode or
momentarily tied the FSI
pin to ground.
x = Don’t care.
SLEEP MODE
The default mode of the 33984 is the Sleep mode. This is
the state of the device after first applying battery voltage
(V_PWR), prior to any I/O transitions. This is also the state of
the device when the WAKE and RST are both Logic [0]. In the
Sleep mode, the output and all unused internal circuitry, such
as the internal 5.0 V regulator, are off to minimize current
draw. In addition, all SPI-configurable features of the device
are as if set to Logic [0]. The device will transition to the
Normal or Fail-safe operating modes based on the WAKE
and RST inputs as defined in Table 6.
NORMAL MODE
The 33984 is in Normal mode when:
• V_PWR is within the normal voltage range.
• RST pin is Logic [1].
• No fault has occurred.
FAIL-SAFE AND WATCHDOG
If the FSI input is not grounded, the watchdog timeout
detection is active when either the WAKE or RST input pin
transitions from Logic [0] to Logic [1]. The WAKE input is
capable of being pulled up to V_PWR with a series of limiting
resistance that limits the internal clamp current according to
the specification.
The watchdog timeout is a multiple of an internal oscillator
and is specified in Table 15. As long as the WD bit (D7) of an
incoming SPI message is toggled within the minimum
watchdog timeout period (WDTO), based on the
programmed value of the WDR the device will operate
normally. If an internal watchdog timeout occurs before the
WD bit, the device will revert to a Fail-safe mode until the
device is reinitialized.
During the Fail-safe mode, the outputs will be ON or OFF
depending upon the resistor RFS connected to the FSI pin,
regardless of the state of the various direct inputs and modes
(Table 7). In this mode, the SPI register content is retained
except for over-current high and low detection levels and
timing, which are reset to their default value (SOCL, SOCH,
and OCLT). Then the watchdog, over-voltage, over-
temperature, and over-current circuitry (with default value)
are fully operational.
Table 7. Output State During Fail-safe Mode
RFS (kΩ)
High Side State
0
Fail-safe mode Disabled
6.0
Both HS0 and HS1 OFF
15
HS0 ON, HS1 OFF
30
Both HS0 and HS1 ON
The Fail-safe mode can be detected by monitoring the
WDTO bit D2 of the WD register. This bit is Logic [1] when the
device is in Fail-safe mode. The device can be brought out of
the Fail-safe mode by transitioning the WAKE and RST pins
from Logic [1] to Logic [0] or forcing the FSI pin to Logic [0].
Table 6 summarizes the various methods for resetting the
device from the latched Fail-safe mode.
If the FSI pin is tied to GND, the watchdog Fail-safe
operation is disabled.
LOSS OF V_DD
If the external 5.0 V supply is not within specification, or
even disconnected, all register content is reset. The two
outputs can still be driven by the direct inputs IN 1:IN0. The
33984 uses the battery input to power the output MOSFET
related current sense circuitry and any other internal logic
providing fail-safe device operation with no V_DD supplied. In
this state, the watchdog, over-voltage, over-temperature, and
over-current circuitry are fully operational with default values.
33984
20
Analog Integrated Circuit Device Data
Freescale Semiconductor