NCV47722
www.onsemi.com
8
APPLICATIONS INFORMATION
Circuit Description
The NCV47722 is an integrated High Side Switch (HSS)
with output current capability up to 250 mA to output. It is
enabled with an input to the enable pin. The integrated
current sense feature provides diagnosis and system
protection functionality. The current limit of the device is
adjustable by resistor connected to CSO pin. Voltage on
CSO pin is proportional to output current. The HSS is
protected by both current limit and thermal shutdown.
Thermal shutdown occurs above 150°C to protect the IC
during overloads and extreme ambient temperatures.
Enable Input
The enable pin is used to turn the regulator on or off. By
holding the pin down to a voltage less than 0.99 V, the output
of the regulator will be turned off. When the voltage on the
enable pin is greater than 2.31 V, the output of the regulator
will be enabled to power its output to the regulated output
voltage. The enable pin may be connected directly to the
input pin to give constant enable to the output regulator.
Setting the Output Current Limit
The output current limit can be set up to 350 mA by
external resistor RCSO (see Figure 1). Capacitor CCSO of
1mF in parallel with RCSO is required for stability of current
limit control circuitry (see Figure 1).
VCSO +Iout ǒRCSO 1
RATIOǓ(eq. 1)
ILIM +RATIO 2.55
RCSO (eq. 2)
RCSO +RATIO 2.55
ILIM (eq. 3)
where
RCSO − current limit setting resistor
VCSO voltage at CSO pin proportional to Iout
ILIM − current limit value
Iout − output current actual value
RATIO − typical value of Output Current to CSO
Current Ratio for particular output current
range
CSO pin provides information about output current actual
value. The CSO voltage is proportional to output current
according to Equation 1.
Once output current reaches its limit value (ILIM) set by
external resistor RCSO than voltage at CSO pin is typically
2.55 V. Calculations of ILIM or RCSO values can be done
using Equation 2 and Equation 3, respectively. Minimum
and maximum value of Output Current Limit can be
calculated according to Equations 4 and 5.
(eq. 4)
ILIM_min +RATIOmin VCSO_min
RCSO_max
(eq. 5)
ILIM_max +RATIOmax VCSO_max
RCSO_min
where
RATIOmin − minimum value of Output Current to
CSO Current Ratio from electrical
characteristics table and particular output
current range
RATIOmax − maximum value of Output Current to
CSO Current Ratio from electrical
characteristics table and particular output
current range
VCSO_min minimum value of CSO Voltage Level at
Current Limit from electrical characteristics
table
VCSO_max maximum value of CSO Voltage Level at
Current Limit from electrical characteristics
table
RCSO_min − minimum value of RCSO with respect its
accuracy
RCSO_max − maximum value of RCSO with respect its
accuracy
Designers should consider the tolerance of RCSO during
the design phase.
Diagnostic in OFF State
The NCV47722 contains also circuitry for OFF state
diagnostics for Short to Battery (STB) and Open Load (OL).
There are internal current source and Pull Down resistors
which provide additional cost savings for overall application
by excluding external components and their assembly cost
and saving PCB space and safe control IOs of a
Microcontroller Unit (MCU).
Simplified functional schematic and truth table is shown
in Figure 13 and related flowchart in Figure 14.