Short Circuit Protection
Short circuits at the DOI output will generate high transient
current until the active current limiting kicks in. In order to
protect the MAX14914 against high currents that can be
seen over an extended time, especially if the output is
switching at a high rate into a short circuit, the MAX14914
enters a protect mode. When the MAX14914 detects that
the DOI current is over 3x higher than the set current
limit, the driver is switched to protect mode with reduced
turn-on slew rate of the rising and falling edges for a duration
of 4ms. The FAULT signal does not become active and
the chip operates normally, but with reduced slew rate. If
the cause for the short circuit is not removed, the protect
mode will remain for an additional 4ms until the short
circuit is removed.
Overvoltage Lockout
When the V
DD
supply voltage exceeds the OVLO threshold
voltage of 42.2V (typ), for a time duration larger than
200μs, the high-side and low-side switches automatically
turn off. They remain off until V
DD
is reduced to below
the threshold OVLO voltage minus hysteresis. When V
DD
is above the OVLO threshold, the OV_VDD output goes
active.
Undervoltage Lockout
When the V
DD
, V5, or VL supply voltages are under their
respective UVLO thresholds the DOI driver is turned off
(three-stated). DOI will automatically turn back on, once
V
DD
, V5, and VL rise above their UVLO threshold.
Driving Capacitive Loads
When charging/discharging purely capacitive loads with
a push-pull driver, the driver dissipates power that is
proportional to the switching frequency. The power can
be estimated by P
D
~ C x V
DD
2
x f, where C is the load
capacitance, V
DD
is the supply voltage, and f is the
switching frequency. For example, in an application with
a 10nF load and 10kHz switching frequency, the driver
dissipates 130mW at V
DD
= 36V. Therefore, switching a
higher capacitance can induce thermal shutdown and that
limits the operational frequency.
Driving Inductive Loads
The DOI pins can be pulled below ground potential when
the high-side transistor is off. The MAX14914 has an
internal clamping diode from V
DD
to DOI that limits the
negative voltage excursion to (V
DD
- 55V) typ. Turning off
the current flowing in ground-connected inductive loads
will result in a negative voltage at DOI pin that is limited
to V
DOI_CL
below V
DD
by the internal clamping diodes.
The MAX14914 features SafeDemag, meaning that there
are no limits for load inductance that it can demagnetize,
for load currents of up to 600mA.
Turn-off of large inductive loads with currents larger than
600mA requires an external clamping diode, as shown in
Figure 5. The clamping (breakdown) voltage of such diode
needs to be less than V
DOI_CL
: V
Z
< V
DOI_CL
. Ensure that
the Zener diode is able to dissipate the energy.
Monitoring of the DOI Output
The driver output (DOI) is monitored in both high-side
and push-pull modes and corresponding logic level can
be seen through the inversed DOI_LVL logic output.
The threshold voltage for the DOI_LVL comparator is
between 1.5V and 2.0V. This feature is useful for
functional safety applications.
Digital Input Operation
The MAX14914 can operate as an industrial digital input.
Drive the DI_EN pin high to enable digital input operation.
The 2.3mA/7mA internal current sink on DIO is then
enabled and the DOI_LVL logic output presents the
inverse of the DOI logic, with threshold voltages compliant
with IEC61131-2 Type 1, Type 2, or Type 3 levels.
Figure 5. External Inductive Load Clamping
V
DD
V
CL
Z
L
DOI
HS
LS
MAX14914
PGND
VZ
MAX14914 High-Side Switch with Settable Current-Limiting,
Push-Pull Driver Option and Digital Input Conguration
www.maximintegrated.com
Maxim Integrated
│
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