MIC280 datasheet(12/23 Pages) MICREL

12 / 23 page

MIC280

Micrel

MIC280

November 2004

Conﬁguration Locking

The security register, LOCK, provides the ability to disable

conﬁguration changes as they apply to the MIC280’s most

critical functions: shutdown mode, and reporting diode faults

andover-temperatureevents. LOCKprovidesawaytoprevent

malicious or accidental changes to the MIC280 registers that

might prevent a system from responding properly to critical

events. Once L0, L1, or L2 has been set, the global interrupt

enable bit, IE, will be set and ﬁxed. It cannot subsequently be

cleared. Its state will be reﬂected in the conﬁguration register.

The bits in LOCK can only be set once. That is, once a bit is

set, it cannot be reset until the MIC280 is power-cycled or a

warm reset is performed by setting RST in the conﬁguration

L4 in LOCK. If L4 is set, locked settings cannot be changed

during operation and warm resets cannot be performed; only

a power-cycle will reset the locked state(s).

If L0 is set, the values of IM0 and CRIT0 become ﬁxed and

unchangeable.Thatis,writestoCRIT0andthecorresponding

interrupt enable bit are locked out. A local over-temperature

event will generate an interrupt regardless of the setting of

IE or its interrupt mask bit.

If L1 is set, the values of IM1 and CRIT1 become ﬁxed and

unchangeable. A remote over-temperature event will gener-

ate an interrupt regardless of the setting of IE or its interrupt

mask bit. Similarly, setting L2 will ﬁx the state of IM2, allow-

ing the system to permanently enable or disable diode fault

interrupts. A diode fault will generate an interrupt regardless

of the setting of IE or its interrupt mask bit.

L3 can be used to lock out shutdown mode. If L3 is set, the

MIC280willnotshutdownunderanycircumstances. Attempts

to set the SHDN bit will be ignored and all chip functions will

remainoperational.IfL3issetwhiletheMIC280isinshutdown

mode, it will immediately exit shutdown mode and resume

normal operation. It will not be possible to subsequently re-

enter shutdown mode.

Setting L4 disables the RST bit in the conﬁguration register,

preventing the host from initiating a warm reset. Writes to

RST will be completely ignored if L4 is set.

LOCK BIT

FUNCTION LOCKED

RESPONSE WHEN SET

Local over-temperature detection

IM0 ﬁxed at 1, writes to CRIT0 locked-out; IE permanently set

Remote over-temperature detection

IM1 ﬁxed at 1; writes to CRIT1 locked-out; IE permanently set

Diode fault interrupts locked on or off

IM2 ﬁxed at current state; IE permanently set if IM2=1

Shutdown mode

SHDN ﬁxed at 0; exit shutdown if SHDN=1 when L3 is set

Warm resets

RST bit disabled; cannot initiate Warm resets

Table 7: Lock bit functionality

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