cs5257a-1 ON Semiconductor, cs5257a-1 Datasheet - Page 8

• Manufacturer Part Number: cs5257a-1
• Description: 7.0 A Ldo 5?pin Adjustable Linear Regulator
• Manufacturer: ON Semiconductor

solution. However, when the circuit operates at low
temperatures, both the value and ESR of the capacitor will
vary considerably. The capacitor manufacturer’s data sheet
provides this information.
applications, but with high current regulators such as the
CS5257A−1 the transient response and stability improve
with higher values of capacitor. The majority of applications
for this regulator involve large changes in load current so the
output capacitor must supply the instantaneous load current.
The ESR of the output capacitor causes an immediate drop
in output voltage given by:
output capacitor network consisting of several tantalum and
ceramic capacitors in parallel. This reduces the overall ESR
and reduces the instantaneous output voltage drop under
transient load conditions. The output capacitor network
should be as close to the load as possible for the best results.
Protection Diodes
regulator it is sometimes necessary to add protection diodes.
If the input voltage of the regulator gets shorted, the output
capacitor will discharge into the output of the regulator. The
discharge current depends on the value of the capacitor, the
output voltage, and the rate at which V
the CS5257A−1 regulator, the discharge path is through a
large junction and protection diodes are not usually needed.
If the regulator is used with large values of output
capacitance and the input voltage is instantaneously shorted
to ground, damage can occur. In this case, a diode connected
as shown in Figure 18 is recommended.
to ground if V
unregulated output from causing system damage.
is required is to solve for current
A 300 mF tantalum capacitor will work for most
For microprocessor applications it is customary to use an
When large external capacitors are used with a linear
Use of the diode has the added benefit of bleeding V
A rule of thumb useful in determining if a protection diode
Figure 18. Diode Protection Against V
Short Circuit Conditions
V
V
CONTROL
CONTROL
POWER
DV + DI
CS5257A−1
Adjust
is shorted. This prevents an
V
ESR
SENSE
V
OUT
CONTROL
CONTROL
drops. In
http://onsemi.com
OUT
8
where:
typical short circuit current value provided in the
specifications, serious thought should be given to the use of
a protection diode.
Current Limit
under excessive load conditions.
Short Circuit Protection
clamps the output current at approximately two amperes less
than its current limit value. This provides for a current
foldback function, which reduces power dissipation under a
direct shorted load.
Thermal Shutdown
activate above a die junction temperature of approximately
150°C and to shut down the regulator output. This circuitry
has 25°C of typical hysteresis, thereby allowing the
regulator to recover from a thermal fault automatically.
Calculating Power Dissipation and
Heat Sink Requirements
operate at high junction temperatures. Therefore, it is
important to calculate the power dissipation and junction
temperatures accurately to ensure that an adequate heat sink
is used. Since the package tab is connected to V
CS5257A−1, electrical isolation may be required for some
applications. Also, as with all high power packages, thermal
compound in necessary to ensure proper heat flow. For
added safety, this high current LDO includes an internal
thermal shutdown circuit.
following four factors: junction temperature, ambient
temperature, die power dissipation, and the thermal
resistance from the die junction to ambient air. The
maximum junction temperature can be determined by:
dissipation are determined by the design while the
maximum junction temperature and the thermal resistance
depend on the manufacturer and the package type. The
maximum power dissipation for a regulator is:
I is the current flow out of the load capacitance when
C is the value of load capacitance,
V is the output voltage, and
T is the time duration required for V
If the calculated current is greater than or equal to the
The internal current limit circuit limits the output current
The device includes short circuit protection circuitry that
The thermal shutdown circuitry is guaranteed by design to
High power regulators such as the CS5257A−1 usually
The thermal characteristics of an IC depend on the
The maximum ambient temperature and the power
V
from high to being shorted.
CONTROL
T J(max) + T A(max) ) PD (max)
is shorted,
I + C
T
V
CONTROL
R QJA
to transition
OUT
on the