LT1933 Linear Technology, LT1933 Datasheet - Page 11

no-image

LT1933

Manufacturer Part Number
LT1933
Description
600mA 500kHz Step-Down Switching Regulator in SOT-23
Manufacturer
Linear Technology
Datasheet

Available stocks

Company
Part Number
Manufacturer
Quantity
Price
Part Number:
LT1933CS6
Manufacturer:
LT
Quantity:
3 495
Part Number:
LT1933CS8
Manufacturer:
LT
Quantity:
10 000
Part Number:
LT1933ES6
Manufacturer:
LT/凌特
Quantity:
20 000
Part Number:
LT1933ES6#PBF
Manufacturer:
LT
Quantity:
12
Part Number:
LT1933ES6#TRMPBF
Manufacturer:
LINEAR
Quantity:
8 000
Part Number:
LT1933ES6#TRMPBF
Manufacturer:
LINEAR/凌特
Quantity:
20 000
Company:
Part Number:
LT1933ES6#TRMPBF
Quantity:
7
Part Number:
LT1933ES6#TRPBF
Manufacturer:
LT
Quantity:
10 460
Part Number:
LT1933ES6#TRPBF
Manufacturer:
AD
Quantity:
100
Part Number:
LT1933ES6#TRPBF
Manufacturer:
LINEAR/凌特
Quantity:
20 000
Part Number:
LT1933ES6TRMPBF
Manufacturer:
LT
Quantity:
120
Part Number:
LT1933HDCB
Manufacturer:
LT
Quantity:
10 000
Part Number:
LT1933HDCB#PBF
Manufacturer:
LINEAR/凌特
Quantity:
20 000
Part Number:
LT1933HDCB#TRMPBF
Manufacturer:
LINEAR/凌特
Quantity:
20 000
APPLICATIO S I FOR ATIO
At light loads, the inductor current becomes discontinu-
ous and the effective duty cycle can be very high. This
reduces the minimum input voltage to approximately
300mV above V
current is continuous and the duty cycle is limited by the
maximum duty cycle of the LT1933, requiring a higher
input voltage to maintain regulation.
Soft-Start
The SHDN pin can be used to soft-start the LT1933,
reducing the maximum input current during start up. The
SHDN pin is driven through an external RC filter to create
a voltage ramp at this pin. Figure 4 shows the start up
waveforms with and without the soft-start circuit. By
choosing a large RC time constant, the peak start up
current can be reduced to the current that is required to
regulate the output, with no overshoot. Choose the value
of the resistor so that it can supply 60µA when the SHDN
pin reaches 2.3V.
OUT
. At higher load currents, the inductor
U
Figure 4. To Soft-Start the LT1933, Add a Resistor and Capacitor to the SHDN Pin.
0.1µF
RUN
U
15k
RUN
SHDN
SHDN
W
V
IN
GND
GND
= 12V, V
1933 F04b
1933 F04a
U
OUT
100mA/DIV
100mA/DIV
= 3.3V, C
5V/DIV
5V/DIV
5V/DIV
5V/DIV
V
V
RUN
RUN
OUT
OUT
I
I
IN
IN
OUT
Shorted and Reversed Input Protection
If the inductor is chosen so that it won’t saturate exces-
sively, an LT1933 buck regulator will tolerate a shorted
output. There is another situation to consider in systems
where the output will be held high when the input to the
LT1933 is absent. This may occur in battery charging
applications or in battery backup systems where a battery
or some other supply is diode OR-ed with the LT1933’s
output. If the V
is held high (either by a logic signal or because it is tied to
V
quiescent current through its SW pin. This is fine if your
system can tolerate a few mA in this state. If you ground
the SHDN pin, the SW pin current will drop to essentially
zero. However, if the V
is held high, then parasitic diodes inside the LT1933 can
= 22µF, R
IN
), then the LT1933’s internal circuitry will pull its
LOAD
0.5ms/DIV
50µs/DIV
= 10Ω.
IN
pin is allowed to float and the SHDN pin
IN
pin is grounded while the output
www.DataSheet4U.com
LT1933
11
1933f

Related parts for LT1933