LTC1624CS8 Linear Technology, LTC1624CS8 Datasheet - Page 14

• 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
Boost Converters: Power MOSFET Selection
One external N-channel power MOSFET must be selected
for use with the LTC1624 for the switch. In boost applica-
tions the source of the power MOSFET is grounded along
with the SW pin. The peak-to-peak gate drive levels are set
by the INTV
approximately 5V for V
can be used. At V
voltage is equal to V
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:
The MOSFET power dissipation at maximum output cur-
rent is given by:
constant inversely related to the gate drive current.
MOSFETs have I
includes an additional term for transition losses that are
highest at high output voltages. For V
current efficiency generally improves with larger MOSFETs,
while for V
to the point that the use of a higher R
lower C
tional information refer to Step-Down Converter: Power
MOSFET Selection in the Applications Information
section.
14
is the temperature dependency of R
P
Main Switch Duty Cycle = 1
where I
MAIN
RSS
OUT
k V
CC
actual provides higher efficiency. For addi-
I
IN MAX
DS(ON)
IN MAX
> 20V the transition losses rapidly increase
voltage. The gate drive voltage is equal to
OUT
2
R losses, plus the P
IN
, reverse transfer capacitance C
U
IN
1 85
– 0.6V and a sublogic level MOSFET
2
voltages below 5V the gate drive
IN
I
OUT MAX
1
INFORMATION
> 5.6V and a logic level MOSFET
I
IN MAX
U
V
V
OUT
IN MIN
V
V
C
W
V
OUT
V
OUT
RSS
D
IN MIN
OUT
V
DS(ON)
DS(ON)
IN
1
MAIN
< 20V the high
200
V
V
D
D
device with
kHz
and k is a
R
U
equation
DS ON
RSS
,
Boost Converter: Inductor Selection
For most applications the inductor will fall in the range of
10 H to 100 H. Higher values reduce the input ripple
voltage and reduce core loss. Lower inductor values are
chosen to reduce physical size.
The input current of the boost converter is calculated at full
load current. Peak inductor current can be significantly
higher than output current, especially with smaller induc-
tors and lighter loads. The following formula assumes
continuous mode operation and calculates maximum peak
inductor current at minimum V
The ripple current in the inductor ( I
30% of the peak inductor current occuring at V
I
with I
Remember boost converters are not short-circuit pro-
tected, and that under output short conditions, inductor
current is limited only by the available current of the input
supply, I
current to safely handle the greater of I
I
rent rating (current when inductance begins to fall)
exceeds the maximum current rating set by R
Boost Converter: R
Output Current
R
Remember the LTC1624 current comparator has a maxi-
mum threshold of 160mV/R
tor threshold sets the peak of the inductor current, yielding
a maximum average output current I
I
divided by the output-input voltage ratio (see equation for
I
OUT(MAX)
OUT(OVERLOAD)
L(PEAK)
L(PEAK)
SENSE
I
L PEAK
I
L
L(MAX)
P-P
)
is chosen based on the required output current.
.
less half the peak-to-peak ripple current ( I
OUT(OVERLOAD)
.
I
OUT MAX
= I
200
. Make sure the inductor’s saturation cur-
V V
IN
L(P-P)
kHz L V
SENSE
OUT
. Specify the maximum inductor
at V
V
Selection for Maximum
IN MIN
V
V
OUT
IN
SENSE
OUT
D
= V
IN
V
:
. The current compara-
IN(MIN)
IN
V
L
D
) is typically 20% to
OUT(MAX)
I
L MAX
.
2
IN(MIN)
SENSE
L(PEAK)
equal to
.
and
L
or
),