MAX14912 Datasheet, PDF (18/30 Pages) Maxim Integrated Products – Low Power and Heat Dissipation

MAX14912/MAX14913
Octal High-Speed, High-Side
Switch/Push-Pull Driver
Watchdog
The watchdog timer allows monitoring activity on the CS
input in serial mode (SRIAL = high). Drive WDEN/IN5 high
to enable the watchdog function. The watchdog monitors
and expects activity on the CS input. The WD timer is
reset at every CS falling edge. If the timer is not reset
after the timeout delay, see Table 8), all OUT_ outputs are
turned off and the watchdog fault output (WDFLTB/IN6)
transitions low until the next CS falling edge.
The watchdog timeout can be selected in SPI command
mode (see the Configuration and Monitoring section). Bits
selection in Register 3: WD[1:0] = 00 for 0.9s, WD[1:0] = 01
for 0.45s and WD[1:0] = 10 for 0.15s. The default value is
0.9s.
Thermal Management
Every driver’s temperature is constantly monitored while
V_DD > V_{DD_UV}. If the temperature of a driver rises above
the thermal-shutdown threshold of T_JSHDN, that channel
is automatically turned off for protection. The drivers are
turned on again once the temperature drops by a hysteresis
margin of T_{JSHDN_HYST}.
Both high and low-side drivers are thermally protected
with a per-driver protection circuit.
When a driver turns off due to thermal shutdown:
1) A fault is indicated through the global FAULT output.
2) The F_ bit of that channel is set in the diagnostic
byte in the SPI interface.
3) The fault LED driver turns on for that channel.
The device also has a chip thermal shutdown that triggers
a FAULT output and all the channels shut down if the tem-
perature rises above T_CSHDN.
Overcurrent and Short-Circuit Protection
In the event of a short-circuit or high current at an OUT_
output, the load current is limited on a per-channel basis
to I_{LIM_HS} for the high-side (HS) driver and to I_{LIM_PP} for
the low-side (LS) driver. Additionally, when a short circuit
is detected, the affected OUT_ output is put in a safe slow-
mode in order to prevent damages in case its IN_ input is
switching at a high frequency. In order to restore normal
operation, the IN_ input of the affected channel has to
be kept low for at least 20ms. While in slow-mode, the
low-to-high and high-to-low transitions at OUT_ are slew-
rate limited to around 3V/µs. A short-circuit or overcurrent
generally creates a temperature rise in the chip; both the
HS and LS FETs’ temperatures are continuously monitored.
When any switch temperature exceeds T_JSHDN, the
corresponding OUT_ output is put in a high-impedance
state until the temperature falls by the hysteresis.
If the case temperature is below T_CSHDN, a short circuit
on one output will allow the other outputs to operate normally.
The HS current-limit circuit features a controlled dV/dI
slope that improves stability with inductive loads. In other
words, the current is limited to a nonconstant value that
increases with (V_DD - V_OUT) with a slope of 1A/150V.
WDEN/IN5
CS
WATCHDOG
WDFLT/IN6
Figure 5. Watchdog Timer
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