Datasheet

LM48100Q
SNAS470D –OCTOBER 2008–REVISED MARCH 2013 www.ti.com
In continuous diagnostic mode, the test sequence is repeated until either a fault condition occurs, DG_RESET is
cycled, or the device is taken out of continuous diagnostic mode. Set DG_CONT = 1 before setting DG_EN = 1
to initiate a continuous diagnostic. Set DG-CONT = 0 to disable continuous diagnostic mode. When the device is
active and DG_EN = 0, the LM48100Q does not perform the output short, or no load diagnostics, however, the
thermal overload and output over current protection circuitry remains active, and disables the device should a
thermal or over-current fault occur. The initial diagnostic operation when power is applied to the device occurs
regardless of the state of DG_EN. The LM48100Q output fault detection can be set to either continuous mode
where the output diagnostic occurs every 60ms, or a one-shot mode. Set bit B3 (DG_CONT) to 1 for continuous
mode, set B3 = 0 for one-shot mode.
Bit B2, DG_RESET, restores the LM48100Q to normal operation after an output fault is detected. Toggle
DG_RESET to re-enable the device outputs and set FAULT high.
Table 4. Diagnostic Control Register
BIT NAME VALUE DESCRIPTION
B0 RESERVED 0 Unused
0 Fixed output current limit
B1 ILIMIT
1 Supply dependent output current limit
Normal operation. FAULT remains low and device is disabled
0
DG
once a fault occurs.
B2
_RESET
1 Reset FAULT output. Device returns to pre-fault operation.
0 One shot diagnostic
DG
B3
_CONT
1 Continuous diagnostic
0 Disable diagnostic
B4 DG_EN
1 Enable diagnostic
FAULT DETECTION CONTROL REGISTER
The LM48100Q output fault tests are individually controlled through the Fault Detection Control register, register
2. Setting any of the bits in the Fault Detection Control register to 1 causes the FAULT circuitry to ignore the
associated test. For example, if B2 (RAIL_SHT) = 1 and the output is shorted to V
DD
, the FAULT output remains
high. Although the FAULT circuitry ignores the selected test, the LM48100Q protection circuitry remains active,
and disables the device. This feature is useful for diagnosing which fault caused a FAULTcondition.
If DG_EN = 1, and a diagnostic sequence is initiated, all the tests are performed regardless of their state in the
Fault Detection Control register. If DG_EN = 0, the RAIL_SHT, OUTPUT_OPEN and OUTPUT_SHT tests are
not performed, however, the thermal overload and output over-current detection circuitry remains active.
Table 5. Fault Detection Control Register
BIT NAME VALUE DESCRIPTION
0 Normal operation
B0 OUTPUT_SHT
1 Ignore output short circuit fault (outputs shorted together)
0 Normal operation
B1 OUTPUT_OPEN
1 Ignore output short circuit fault
0 Normal operation
RAIL
B2
_SHT
1 Ignore output short to V
DD
or GND fault
0 Normal operation
B3 OVF
1 Ignore output over-current fault
0 Normal operation
B4 TSD
1 Ignore thermal overload fault
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