LTC1735CS-1 Linear Technology, LTC1735CS-1 Datasheet - Page 22

• Manufacturer Part Number: LTC1735CS-1
• Description: IC REG SW SYNC STEPDWN HE 16SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1735CS-1

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 6 V
• Current - Output: 3A
• Frequency - Switching: 300kHz
• Voltage - Input: 4 ~ 30 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
LTC1735-1
The next step is to calculate the I
factor. The V
required for a given load current in continuous inductor
current operation. V
voltage, which represents the DC output current plus one
half of the peak-to-peak inductor current. The no load to
full load V
the sense resistor voltage from 0V to the V
voltage of 75mV. For the circuit shown in Figure 8, the
calculated V
Assuming continuous inductor current, V
At full load current:
At minimum load current:
Notice that I
from light load to full load. Increasing the DC inductor
current decreases the permeability of the inductor core
material, which decreases the inductance and increases
inductor design.
If the circuit shown in Figure 8 sustained continuous in-
ductor current operation, the error amplifier would control
22
V
ITH
I
L
V
V
V
. The amount of inductance change is a function of the
ITH
ITH MAX
ITH MIN
Scale Factor
(
(
ITH
)
V
)
ITH
I
ITH
OUTDC
L
ITH
range is from 0.3V to 2.4V, which controls
, the peak-to-peak inductor current, changes
1 77
0 40
scale factor is:
Offset
.
.
scale factor reflects the I
0 2
15
.
U
V
V
ITH
( .
A
A
V
2 4
ITH
2
I
controls the peak sense resistor
L
5
V
2
Range Sense
U
A
A
– .
2
•
P P
2
0 075
P P
0 3
.
V
ITH
TH
V
•
V
• .
• .
) • .
Scale Factor
V
pin voltage, V
SENSE MAX
0 084
0 084
W
0 003
(
Re
V A
V A
ITH
TH
/
/
sistor Value
)
is:
0 084
pin voltage
SENSE(MAX)
.
U
ITH
0 3
0 3
.
.
, scale
V A
V
V
/
V
change. During Burst Mode operation, the LTC1735-1
output voltage is controlled by a comparator, not the error
amplifier. Even though the error amplifier is not used in
Burst Mode operation, it is necessary to assume linear
operation for all error amplifier gain calculations.
To create the 30mV input offset error, the voltage gain of
the error amplifier must be limited. The desired gain is:
Connecting a resistor to the output of the transconductance
error amplifier will limit the voltage gain. The value of this
resistor is:
To center the output voltage variation, V
centered so that no I
voltage is nominal. V
tween V
output current:
The Thevenin equivalent of the gain limiting resistance
value of 17.54k is made up of a resistor R5 that sources
current into the I
to SGND.
To calculate the resistor values, first determine the ratio
between them:
V
Resistor R5 is:
ITH
INTVCC
R
k
R
A
V
ITH NOM
ITH
5
from 0.40V at light load to 1.77V at full load, a 1.37V
V
(
V
is equal to V
INTVCC
(
ITH
Input Offset Error
k
Error Amplifier g
)
at maximum output current and minimum
V
1
ITH NOM
) •
1 77
–
V
R
(
TH
.
V
ITH MAX
V
ITH
ITH
A
ITH NOM
pin and resistor R1 that sinks current
(
V
TH
V
EXTVCC
)
ITH(NOM)
(
– .
2
pin current flows when the output
( .
0 40
3 79 1 17 54
)
2
–
)
or 5.2V if EXTV
m
V
ITH MIN
V
2 0 03
5 2
is the average voltage be-
( .
1 37
.
(
) •
1 3
.
0 40
22 8
V
.
1 085
.
.
ms
– .
)
.
V
V
1 085
.
V
)
V
V
ITH MIN
k
17 54
1 085
22 8
CC
(
.
ITH
V
.
84 0
.
is not used.
.
)
must be
k
3 79
V
k
.