LT1933IS6#PBF Linear Technology, LT1933IS6#PBF Datasheet - Page 11

• Manufacturer Part Number: LT1933IS6#PBF
• Description: IC, STEP-DOWN REGULATOR, 6-TSOT-23
• Manufacturer: Linear Technology

Specifications of LT1933IS6#PBF

• Primary Input Voltage: 36V
• No. Of Outputs: 1
• Output Current: 600mA
• No. Of Pins: 6
• Operating Temperature Range: -40°C To +125°C
• Supply Voltage Range: 3.6V To 36V
• Switching Frequency Max: 600kHz
• Msl: MSL 1 - Unlimited
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
BOOST Pin Considerations
Capacitor C3 and diode D2 are used to generate a boost
voltage that is higher than the input voltage. In most cases
a 0.1μF capacitor and fast switching diode (such as the
1N4148 or 1N914) will work well. Figure 2 shows two
ways to arrange the boost circuit. The BOOST pin must
be at least 2.3V above the SW pin for best effi ciency. For
outputs of 3V and above, the standard circuit (Figure 2a)
is best. For outputs between 2.5V and 3V, use a 0.47μF
capacitor and a small Schottky diode (such as the BAT-54).
For lower output voltages the boost diode can be tied to
the input (Figure 2b). The circuit in Figure 2a is more ef-
fi cient because the BOOST pin current comes from a lower
voltage source. You must also be sure that the maximum
voltage rating of the BOOST pin is not exceeded.
6.0
5.5
5.0
4.5
4.0
3.5
3.0
Minimum Input Voltage V
1
V
IN
Figure 3. The Minimum Input Voltage Depends on Output Voltage, Load Current and Boost Circuit
TO START
TO RUN
V
MAX V
BOOST
LOAD CURRENT (mA)
10
BOOST
V
IN
– V
SW
BOOST
LT1933
≅ V
GND
≅ V
IN
OUT
+ V
SW
OUT
100
Figure 2. Two Circuits for Generating the Boost Voltage
OUT
V
T
L = 22μH
(2a)
A
OUT
= 25°C
= 3.3V
= 3.3V
1933 F03a
C3
D2
1933 F02a
V
OUT
The minimum operating voltage of an LT1933 application
is limited by the undervoltage lockout (~3.35V) and by
the maximum duty cycle as outlined above. For proper
startup, the minimum input voltage is also limited by the
boost circuit. If the input voltage is ramped slowly, or the
LT1933 is turned on with its SHDN pin when the output
is already in regulation, then the boost capacitor may not
be fully charged. Because the boost capacitor is charged
with the energy stored in the inductor, the circuit will rely
on some minimum load current to get the boost circuit
running properly. This minimum load will depend on input
and output voltages, and on the arrangement of the boost
circuit. The minimum load generally goes to zero once the
circuit has started. Figure 3 shows a plot of minimum load
to start and to run as a function of input voltage. In many
V
IN
V
MAX V
BOOST
V
BOOST
8
7
6
5
4
D2
IN
– V
1
Minimum Input Voltage V
SW
BOOST
LT1933
≅ 2V
GND
≅ V
TO START
TO RUN
IN
IN
SW
LOAD CURRENT (mA)
(2b)
10
C3
1933 F02b
100
OUT
V
T
L = 33μH
OUT
A
= 25°C
= 5V
1933 F03b
= 5V
V
OUT
LT1933
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