LTC4222
17
4222fb
APPLICATIONS INFORMATION
Fault Alerts
When any of the fault bits in a FAULT register (see Table 4) 
are set, an optional bus alert is generated if the appropri-
ate bit in the ALERT register has been set. This allows 
only selected faults to generate alerts. At power-up the 
default state is to not alert on faults and the ALERT pin 
is high. If an alert is enabled, the corresponding fault 
causes the ALERT pin to pull low. After the bus master 
controller broadcasts the Alert Response Address, the 
LTC4222 responds with its address on the SDA line and 
releases ALERT as shown in Table 7. If there is a collision 
between two LTC4222s responding with their addresses 
simultaneously, then the device with the lower address 
wins arbitration and responds first. The ALERT line is also 
released if the device is addressed by the bus master if 
ALERT is pulled low due to an alert.
Once the ALERT signal has been released for one fault, it 
is not pulled low again until the FAULT register indicates a 
different fault has occurred or the original fault is cleared 
and it occurs again. Note that this means repeated or 
continuing faults do not generate alerts until the associ-
ated FAULT register bit has been cleared.
Resetting Faults
Faults are reset with any of the following conditions on a 
given channel. First, a serial bus command writing zeros 
to the FAULT register bits 0 to 5 clears the associated 
faults. Second, FAULT register bits 0 to 5 are cleared when 
the corresponding switch is turned off by the ON pin or 
STATUS bit 3 going from high to low, if the corresponding 
UV pin is brought below its 0.4V reset threshold for 2祍, 
or if INTV
CC
 falls below its 2.64V undervoltage lockout 
threshold. Finally, when EN is brought from high to low, 
only corresponding FAULT bits 0-3 and 5 are cleared, and 
bit 4, which indicates a EN change of state, is set. Note 
that faults that are still present, as indicated in the STATUS 
registers, cannot be cleared.
The FAULT registers are not cleared when auto-retrying. 
When auto-retry is disabled the existence of an overvoltage, 
undervoltage, or overcurrent fault keeps the switch off. 
As soon as the fault is cleared, the switch turns on. If 
auto-retry is enabled, then a high value in STATUS register 
bits 0 or 1 holds the switch off and the fault register is 
ignored. Subsequently, when STATUS register bits 0 and 
1 are cleared by removal of the fault condition, the switch 
is allowed to turn on again. The LTC4222 will set FAULT 
bit 2 and turn off in the event of an overcurrent fault, 
preventing it from remaining in an overcurrent condition. 
If configured to auto-retry, the LTC4222 will continually 
attempt to restart after cool-down cycles until it succeeds 
in starting up without generating an overcurrent fault. Note 
that if a switch is on after an auto-retry and the FAULT bit 
has not been reset, clearing the corresponding auto-retry 
bit will turn the channel off.
Data Converter
The LTC4222 incorporates a 10-bit A/D converter that 
continuously scans six different voltages. The SOURCE 
pins have a 1/24 resistive divider to monitor a full-scale 
voltage of 32V with 31.25mV resolution. The ADIN pins are 
monitored with a 1.28V full scale and 1.25mV resolution, 
and the voltage between the V
DD
 and SENSE pins is moni-
tored with a 64mV full scale and 62.5礦 resolution.
Results from each conversion are stored, left justified, in 
registers as seen in Tables 7 and 8, and are updated 15 
times per second. Setting ADC_CONTROL register bit 0 
invokes a test mode that halts the data converter so that 
the data converter result registers may be written to and 
read from for software testing.
The data converter also has a direct address mode that 
allows the user to take a specific measurement at a spe-
cific time and hold that value for later readback. Direct 
address mode is entered by setting the Halt bit, bit 0, in 
the ADC_CONTROL register (see Table 9). Then when 
the channel address bits, ADC_CONTROL bits 1 to 3, are 
written to, the ADC will make a single measurement on 
the channel indicated by those bits, then stop. Setting the 
ADC Alert bit, ADC_CONTROL bit 4, will enable an interrupt 
when the data converter finishes the conversion, result-
ing in the ALERT pin pulling low when the data is ready. 
Alternately, the ADC Busy bit, ADC_CONTROL bit 5, can 
be polled to check for the end of the conversion, after a 
direct address conversion the ADC Busy bit will go low. In 
normal mode ADC Busy is always high. Resetting the Halt 
bit returns the data converter to the scan mode.