LM350BT Motorola, LM350BT Datasheet - Page 7

• Manufacturer Part Number: LM350BT
• Description: Search -----> LM350
• Manufacturer: Motorola

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Basic Circuit Operation
operation, the LM350 develops and maintains a nominal
1.25 V reference (V ref ) between its output and adjustment
terminals. This reference voltage is converted to a
programming current (I PROG ) by R 1 (see Figure 17), and this
constant current flows through R 2 to ground. The regulated
output voltage is given by:
error term in the equation, the LM350 was designed to control
I Adj to less than 100 A and keep it constant. To do this, all
quiescent operating current is returned to the output terminal.
This imposes the requirement for a minimum load current. If
the load current is less than this minimum, the output voltage
will rise.
voltage differential across the circuit which is important to
performance, and operation at high voltages with respect to
ground is possible.
Load Regulation
regulation, but a few precautions are needed to obtain
maximum performance. For best performance, the
programming resistor (R 1 ) should be connected as close to
the regulator as possible to minimize line drops which
effectively appear in series with the reference, thereby
degrading regulation. The ground end of R 2 can be returned
near the load ground to provide remote ground sensing and
improve load regulation.
MOTOROLA ANALOG IC DEVICE DATA
The LM350 is a three–terminal floating regulator. In
Since the current from the terminal (I Adj ) represents an
Since the LM350 is a floating regulator, it is only the
The LM350 is capable of providing extremely good load
Figure 17. Basic Circuit Configuration
V in
V ref = 1.25 V Typical
V out = V ref (1 +
Adjust
LM350
I Adj
V ref
R 2
R 1
V out
) + I Adj R 2
+
R 2
R 1
I PROG
APPLICATIONS INFORMATION
V out
LM350
External Capacitors
is recommended to reduce the sensitivity to input line
impedance.
improve ripple rejection. This capacitor (C Adj ) prevents ripple
from being amplified as the output voltage is increased. A
10 F capacitor should improve ripple rejection about 15 dB
at 120 Hz in a 10 V application.
like any feedback circuit, certain values of external
capacitance can cause excessive ringing. An output
capacitance (C O ) in the form of a 1 F tantalum or 25 F
aluminum electrolytic capacitor on the output swamps this
effect and insures stability.
Protection Diodes
is sometimes necessary to add protection diodes to prevent
the capacitors from discharging through low current points
into the regulator.
protection diodes for output voltages in excess of 25 V or high
capacitance values (C O > 25 F, C Adj > 10 F). Diode D 1
prevents C O from discharging thru the IC during an input
short circuit. Diode D 2 protects against capacitor C Adj
discharging through the IC during an output short circuit. The
combination of diodes D 1 and D 2 prevents C Adj from
discharging through the IC during an input short circuit.
A 0.1 F disc or 1 F tantalum input bypass capacitor (C in )
The adjustment terminal may be bypassed to ground to
Although the LM350 is stable with no output capacitance,
When external capacitors are used with any IC regulator, it
Figure 18 shows the LM350 with the recommended
V in
C in
Figure 18. Voltage Regulator with
Adjust
Protection Diodes
1N4002
LM350
D 1
R 2
R 1
V out
C Adj
D 2
1N4002
+
C O
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