MAX14900E Datasheet, PDF (16/31 Pages) Maxim Integrated Products – Global and Per-Channel Diagnostics

MAX14900E
Octal, High-Speed, Industrial, High-Side Switch
Thermal Shutdown Protection
Thermal overload circuitry constantly monitors each
switch/driver and a global thermal shutdown circuit
monitors average chip temperature. When a local thermal
shutdown condition occurs for one of the drivers, it is
disabled while the others continue to operate. When the
local temperature falls to below the activation thresh-
old (T_{C_SD} – T_{C_SD_HYS}), that driver automatically
re-enables. A global thermal shutdown does not disable
the O_ outputs but prevents any channel from re-enabling
itself until the global temperature sensor is below the limit.
The FAULT output is asserted when any thermal shut-
down condition occurs. In addition, F_ bits are set for
channels that are in thermal shutdown in the SPI SDO
data.
Overload and Short-Circuit Protection
The device protects each O_ output against overload and
short-circuit conditions while operating in push-pull and
high-side mode.
In high-side mode, the device actively limits each chan-
nel’s output current to 1.7A. As long as no thermal
shutdown occurs, this current limiting condition persists
continuously.
In push-pull mode, the device limits the load current to
300mA/500mA (typ). Overload faults are detected when
an O_ output is in push-pull mode and an overcurrent
condition forces the output voltage to above 1V (for O_ = low)
or below (V_DD - 1V) (for O_ = high) for more than the
blanking time 90µs (typ). When the cause of the output
voltage level mismatch is removed, the driver resumes
normal operation.
POR and UVLO Conditions
The MAX14900E features undervoltage lockout (UVLO)
and power-on reset (POR) circuitry on its power supply
inputs to ensure that the device is in a known state
on power-up or when there is a droop on one of the
supplies. If either V_L or V₅ falls to below its POR threshold,
the device goes into its reset state and all configuration
settings are lost.
When V_DD or V₅ is below its UVLO threshold, all O_
outputs are disabled and the 80µA open-load detection
current sources are turned off. The device resumes nor-
mal operation when the UVLO condition is removed. As
long as V_L and V₅ stay above their POR thresholds, the
SPI interface remains active and configuration settings
are not affected.
In 16-bit serial mode when a UVLO is present, a series
of all ones in the serial SDO status/fault read back bits
reports this condition.
FAULT Output
The global FAULT output asserts when a fault condition is
detected on any O_ output. The types of fault conditions
reported by FAULT are thermal shutdown, open-load (if
enabled), and overload protection (in push-pull mode
only). The global FAULT is not initiated in a UVLO condition.
Thermal shutdown faults are detected when the
internal temperature of any driver exceeds the thermal
shutdown threshold (T_{C_SD}). The fault is cleared when the
temperature falls to below the activation threshold (T_{C_SD}
– T_{C_SD_HYS}).
Open-load faults are detected when the voltage at an O_
output in high-side mode with the HS switch turned off is
above the detection threshold of 7V. This happens when
the O_ output is not connected to any external load and
the 80µA pullup current charges the node. A brief open-
load condition can occur after an HS switch is turned off
and the load has not discharged capacitance yet.
In push-pull mode, if the voltage level at an O_ output dif-
fers from the programmed value for longer than the 90µs
(typ) blanking time due to overcurrent, the driver is turned
off for the 11ms (typ) retry time. During the retry period,
the FAULT output is asserted and the fault bit is set for
that driver in the serial data. The fault is cleared after the
fault condition is removed at the end of the current retry
period (11ms).
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