NCS5652, NCV5652
www.onsemi.com
9
APPLICATIONS INFORMATION
Figure 22 shows a typical application on how to connect
the NCx5652 pins where the V
CC
is supplied by 5 V and the
output stages are supplied with 12 V. In this configuration
the inputs can be driven up to 3.8 V. The outputs can be as
high as 4 V and able to go near ground due to the excellent
V
OL
parameters. The loads can be up to 500 mA continuous.
Power Supply
The supply pins should be properly bypassed with
ceramic 0.1 mF to 1 mF capacitors. The different supply pins
for the input stage (V
CC
) and the output stage (VC1,VC2)
provide a flexible power option. In many applications there
is often a digital supply and different supply for driving
motors or elements. The output stage can be optimized for
the voltage requirements of the load. There are no
requirements on the voltage levels (as long as they are within
specification) and sequencing of the V
CC
, VC1, and VC2
pins. It should be noted that the input and output swings are
a function of V
CC
. The common mode voltage range and
output swings are specified in the electrical section
according to the V
CC
voltage.
Shutdown Feature
The NCx5652 provides a thermal shutdown feature to
protect the device during fault conditions (See Output Short
Circuit Protection section). Pin 3 is an open collector output
that can be connected to a microcontroller to alert the system
that a thermal shutdown has occurred. The thermal
shutdown circuit has approximately 20°C hysteresis. When
the device is in a thermal shutdown condition, the outputs
are tri−stated. The same pin can be used for an input as well.
It can be open collector OR’d so that the microcontroller can
disable the device by driving this pin low. This pin must
always be pulled high via a 10 kW resistor (recommended
value). It should always be driven with an open
collector/drain device. Some microcontrollers have open
drain configurable outputs.
Stability
The NCx5652 is designed to drive large capacitive loads
and not oscillate even at unity gain. It is recommended that
a minimum of 0.1 mF capacitor be placed on the outputs to
ensure stability. This is mainly required for no load or light
load conditions. If configuring the device as a follower, it is
also recommended to use a 10 kW feedback resistor as
shown in Figure 22.
Thermal Considerations
As power in the NCx5652 increases, it might become
necessary to provide some thermal relief. The maximum
power dissipation supported by the device is dependent
upon board design and layout. Mounting pad configuration
on the PCB, the board material, and the ambient temperature
affect the rate of junction temperature rise for the part. When
the NCS5652 has good thermal conductivity through the
PCB, the junction temperature will be relatively low with
high power applications. The maximum dissipation the
NCx5652 can handle is given by:
P
D(MAX)
+
ƪ
T
J
ǒ
MAX
Ǔ
* T
A
ƫ
R
qJA
(eq. 1)
Since T
J
is not recommended to exceed 150°C, then the
NCx5652 soldered on 1200 mm
2
, 1 oz copper area, FR4 can
dissipate up to 2.5 W when the ambient temperature (T
A
) is
25°C.
Output Short Circuit Protection
The NCx5652 is designed to withstand short circuits on
the outputs. With proper application design, the outputs can
be shorted to ground or to a source up to 16 V without
damage. Depending on the ambient temperature and thermal
conductivity of the PCB, the device may enter thermal
shutdown during a short circuit event. Even though the
thermal shutdown disables the outputs, the application
should not allow the outputs to be enabled continuously
during a short circuit event when a thermal shutdown occurs.
The DISABLE
/Tflag pin (pin 3) should be monitored to
recognize when a thermal shutdown event happens. And
then respond within 5ms to disable the outputs for a
minimum of 5 seconds (DIS and DIS
HOLD
parameters in
Figure 23). This low duty cycle keeps the device average
junction temperature in a safe zone.
• Output Short to Source
When it is possible that the NCx5652 can be shorted to a
source higher than VC1, VC2, a diode (D1) should be used
to prevent current flow going back to the VC1,VC2 source
as shown in Figure 22. The worst case for this event is when
V
OUT
is low (V
OL
). Figure 23 shows a diagram short from
low to high (V
OUT
= V
OL
shorted to 12 V−16 V). Note that
when the short circuit current (I
SC
) is low, the device is either
operating normal or the outputs are disabled (tri−stated).
Table 6 shows typical values for I
SC−PK
and I
SC−CLAMP
. The
parameter I
SC−HOLD
is the time it takes the device to enter
thermal shutdown. This parameter varies depending on the
ambient temperature and the thermal conductivity of the
PCB. If the device thermal limit is not reached, the output
current will stay clamped to the I
SC−CLAMP
value.
As stated earlier, the device should be disabled as soon as
thermal shutdown occurs (noted by T
SHDN
in figure 23).
After T
SHDN
occurs the device thermal shutdown circuit
will disable the outputs for approximately 20ms before
enabling them again (a characteristic from the thermal
shutdown hysteresis). To allow variations of conditions, it is
recommended that the microcontroller responds within 5ms
(DIS parameter in Table 6) to keep pin 3 low. After a
minimum of 5 seconds the microcontroller can then enable
the outputs (indicated by the EN in Figure 23). This cycle
will repeat until the short is removed from the outputs.
Figures 24 thru 26 show some typical values for an example
