LTC1624CS8 Linear Technology, LTC1624CS8 Datasheet - Page 18

• Manufacturer Part Number: LTC1624CS8
• Description: IC SW REG CONTROLLER N-CH 8-SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Step-Up (Boost), Inverting, Sepicr

Specifications of LTC1624CS8

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.19 ~ 30 V
• Current - Output: 2A
• Frequency - Switching: 200kHz
• Voltage - Input: 3.5 ~ 36 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

LTC1624
APPLICATIONS
that the voltage across C1 is constant such that V
at full load over the entire V
storage in the coupling capacitor C1 must be equal to the
enegry stored in L1, the minimum capacitance of C1 is:
SEPIC Converter: Duty Cycle Limitations
The minimum on-time of 450ns sets a limit on how high
an input-to-output ratio can be tolerated while not skip-
ping cycles. This only impacts designs when very low
output voltages (V
SEPIC converter would not be appropriate at these low
output voltages. The maximum input voltage is (remem-
ber not to exceed the absolute maximum limit of 36V):
Positive-to-Negative Converter Applications
The LTC1624 can also be used as a positive-to-negative
converter with a grounded inductor shown in Figure 8.
Since the LTC1624 requires a positive feedback signal
relative to device ground, Pin 4 must be tied to the
regulated negative output. A resistive divider from the
negative output to ground sets the output voltage.
Remember not to exceed maximum V
18
V
C
OUT
100pF
V
R
1
IN(MAX)
C
MIN
C
C
36V.
Figure 8. Positive-to-Negative Converter
1
2
3
4
= 10.1V
L I
SENSE
I
V
GND
TH
1
FB
/RUN
OUT
V
LTC1624
–
IN MIN
OUT
U
OUT
2
BOOST
< 2.5V) are needed. Note that a
V
+ 5V
SW
1000pF
V
TG
INFORMATION
OUT
IN
4
U
IN
8
7
6
5
range. Assuming the enegry
2
For DC > 9%
C
B
W
D1
V
IN
M1
R
IN
SENSE
R1
R2
L1
ratings V
U
+
+
C1
C
C
= V
IN
OUT
–V
1624 F08
IN
OUT
IN
+
Positive-to-Negative Converter: Output Voltage
Programming
Setting the output voltage for a positive-to-negative con-
verter is different from other architectures since the feed-
back voltage is referenced to the LTC1624 ground pin and
the ground pin is referenced to – V
is set by a resistive divider according to the following
formula:
The external resistive divider is connected to the output as
shown in Figure 8.
Positive-to-Negative Converter: Power
MOSFET Selection
One external N-channel power MOSFET must be selected
for use with the LTC1624 for the switch. As in step-down
applications the source of the power MOSFET is con-
nected to the Schottky diode and inductor. The peak-to-
peak gate drive levels are set by the INTV
gate drive voltage is equal to approximately 5V for V
5.6V and a logic level MOSFET can be used. At V
below 5V the INTV
sublogic level MOSFET should be used.
Selection criteria for the power MOSFET include the “ON”
resistance R
input voltage and maximum output current. When the
LTC1624 is operating in continuous mode the duty cycle
for the MOSFET is given by:
with V
The MOSFET power dissipation and maximum switch
current are given by:
P
Main
V
MAIN
OUT
OUT
Switch Duty Cycle =
= I
1 19
{
I
k V
SW MAX
DS(ON)
being the absolute value of V
OUT MAX
V
IN MAX
1
CC
, reverse transfer capacitance C
voltage is equal to V
R
R
2
1
I
V
OUT
R
V
V
IN
DS ON
IN
OUT
V
1.85
1
OUT
. The output voltage
V
DC
OUT
DC
C
CC
IN
RSS
V
OUT
D
– 0.6V and a
voltage. The
V
IN
.
D
200kHz
voltages
RSS
IN
>
,
{