LT1073CS8 Linear Technology, LT1073CS8 Datasheet - Page 9

• Manufacturer Part Number: LT1073CS8
• Description: IC DC/DC CONVERTER ADJSTBL 8SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Step-Up (Boost), Invertingr

Specifications of LT1073CS8

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: Adjustable
• Current - Output: 400mA
• Frequency - Switching: 19kHz
• Voltage - Input: 1 ~ 30 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Power - Output: 500mW
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
switch is in series with the output. Step-down converters
are characterized by low output voltage ripple but high
input current ripple. The usual hookup for an LT1073-
based step-down converter is shown in Figure 7.
When the switch turns on, SW2 pulls up to V
puts a voltage across L1 equal to V
causing a current to build up in L1. At the end of the switch
ON time, the current in L1 is equal to
When the switch turns off the SW2 pin falls rapidly and
actually goes below ground. D1 turns on when SW2
reaches 0.4V below ground. D1 MUST BE A SCHOTTKY
DIODE . The voltage at SW2 must never be allowed to go
below –0.5V. A silicon diode such as the 1N4933 will allow
SW2 to go to –0.8V, causing potentially destructive power
dissipation inside the LT1073. Output voltage is deter-
mined by
Step-Down (Buck Mode) Operation
A step-down DC/DC converter converts a higher voltage to
a lower voltage. It is short-circuit protected because the
i
V
V
PEAK
OUT
OUT
V
C2
IN
+
V
1
1
IN
Figure 7. Step-Down Mode Hookup
220
–
R3
R
R
R
R
I
V
LIM
2
1
2
1
SW
LT1073
U
L
GND
V
212
212
IN
–
SW1
SW2
1N5818
V
FB
mV
mV
OUT
U
D1
t
ON
L1
C1
W
+
IN
– V
IN
SW
– V
R2
R1
1073 FO7
U
V
OUT
SW
– V
. This
OUT
,
R3 programs switch current limit. This is especially im-
portant in applications where the input varies over a wide
range. Without R3, the switch stays on for a fixed time
each cycle. Under certain conditions the current in L1 can
build up to excessive levels, exceeding the switch rating
and/or saturating the inductor. The 220
grams the switch to turn off when the current reaches
approximately 400mA. When using the LT1073 in step-
down mode, output voltage should be limited to 6.2V or
less.
Inverting Configurations
The LT1073 can be configured as a positive-to-negative
converter (Figure 8), or a negative-to-positive converter
(Figure 9). In Figure 8, the arrangement is very similar to
a step-down, except that the high side of the feedback is
referred to ground. This level shifts the output negative. As
in the step-down mode, D1 must be a Schottky diode, and
V
OUT
+V
–V
IN
C2
IN
should be less than 6.2V.
+
+
Figure 8. Positive-to-Negative Converter
Figure 9. Negative-to-Positive Converter
C2
R3
AO
GND
I
LIM
I
LIM
LT1073
LT1073
GND
V
IN
SW2
SW1
V
SW1
SW2
IN
FB
1N5818
FB
L1
D1
V
R2
OUT
L1
D1
=
+
( )
+
R1
R2
C1
C1
212mV + 0.6V
LT1073
2N3906
resistor pro-
R1
R1
R2
+V
1073 F09
–V
OUT
1073 FO8
OUT
9