MC33269T Просмотр технического описания (PDF) - Motorola => Freescale
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MC33269T Datasheet PDF : 8 Pages
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MC33269
APPLICATIONS INFORMATION
Figures 10 through 14 are typical application circuits. The
output current capability of the regulator is in excess of
800 mA, with a typical dropout voltage of less than 1.0 V.
Internal protective features include current and thermal
limiting.
The MC33269 is not internally compensated and thus
requires an external output capacitor for stability. The
capacitor should be at least 10 µF with an equivalent series
resistance (ESR) of less than 10 Ω over the anticipated
operating temperature range. With economical electrolytic
capacitors, cold temperature operation can pose a problem.
As temperature decreases, the capacitance also decreases
and the ESR increases, which could cause the circuit to
oscillate. Solid tantalum capacitors may be a better choice if
small size is a requirement. Also capacitance and ESR of a
solid tantalum capacitor is more stable over temperature. An
input bypass capacitor is recommended to improve transient
response or if the regulator is connected to the supply input
filter with long wire lengths. This will reduce the circuit’s
sensitivity to the input line impedance at high frequencies. A
0.33 µF or larger tantalum, mylar, ceramic, or other capacitor
having low internal impedance at high frequencies should be
chosen. The bypass capacitor should be mounted with
shortest possible lead or track length directly across the
regulator’s input terminals. Applications should be tested
over all operating conditions to insure stability.
Internal thermal limiting circuitry is provided to protect the
integrated circuit in the event that the maximum junction
temperature is exceeded. When activated, typically at 170°C,
the output is disabled. There is no hysteresis built into the
thermal limiting circuit. As a result, if the device is
overheating, the output will appear to be oscillating. This
feature is provided to prevent catastrophic failures from
accidental device overheating. It is not intended to be used
as a substitute for proper heatsinking.
Figure 10. Typical Fixed Output Application
Figure 11. Typical Adjustable Output Application
Vin
Vout
MC33269–XX
Cin
CO
10 µF
Gnd
An input capacitor is not necessary for stability, however
it will improve the overall performance.
Figure 12. Current Regulator
Vin
RS
Iout
MC33269
Cin
CO
10 µF
Adj
+ Iout
1.25
RS
Vin
Vout
MC33269
Cin
R1
Adj
CO
10 µF
R2
CAdj*
ǒ Ǔ + ) ) Vout
1.25
1
R2
R1
IAdj R2
*CAdj is optional, however it will improve the ripple rejection.
The MC34269 develops a 1.25 V reference voltage between the
output and the adjust terminal. Resistor R1, operates with
constant current to flow through it and resistor R2. This current
should be set such that the Adjust Pin current causes negligible
drop across resistor R2. The total current with minimum load
should be greater than 8.0 mA.
Figure 13. Battery Backed–Up Power Supply
Figure 14. Digitally Controlled Voltage Regulator
Vin
Vout
MC33269–XX
Cin
Gnd
Vin
Vout
MC33269
Cin
R1
Adj
CO
10 µF
R2
MC33269–XX
Cin
CO
10 µF
Gnd
The Schottky diode in series with the ground leg of the upper
regulator shifts its output voltage higher by the forward
voltage drop of the diode. This will cause the lower device
to remain off until the input voltage is removed.
6
R2 sets the maximum output voltage. Each transistor
reduces the output voltage when turned on.
MOTOROLA ANALOG IC DEVICE DATA
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