LTC1624IS8 Linear Technology, LTC1624IS8 Datasheet - Page 13

• Manufacturer Part Number: LTC1624IS8
• Description: IC SW REG CONTROLLER N-CH 8-SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Step-Up (Boost), Inverting, Sepicr

Specifications of LTC1624IS8

• 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: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIONS
100 resistor in series with the SENSE
cancels the internal offset in current comparator I
to Functional Diagram). This comparator in conjunction
with the voltage on the I
enter into Burst Mode operation (refer to Low Current
Operation in Operation section). With the additional exter-
nal offset present, the drive to the topside MOSFET is
always enabled every cycle and constant frequency opera-
tion occurs for I
Step-Down Converter: Design Example
As a design example, assume V
V
immediately be calculated:
Assume a 10 H inductor. To check the actual value of the
ripple current the following equation is used:
The highest value of the ripple current occurs at the
maximum input voltage:
The power dissipation on the topside MOSFET can be
easily estimated. Choosing a Siliconix Si4412DY results
in: R
voltage with T(estimated) = 50 C:
The most stringent requirement for the Schottky diode
occurs when V
In this case the worst-case dissipation rises to:
P
MAIN
IN
3 3
22
R
P
= 22V(max), V
2 5 22
D
SENSE
I
I
DS(ON)
V
L
L
V
I
SC AVG
0 5
0 5
200
V
= 100mV/2A = 0.05
IN
V
22
= 0.042 , C
V
V
1 85
f L
kHz
V
OUT
V
2
OUT
OUT
A
2
V
3 3
10
= 0V (i.e. short circuit) at maximum V
OUT
2
A
D
U
> I
1
V
100
H
V
V
= 3.3V and I
OUT(MIN)
V
OUT
IN
RSS
TH
0 005 50
IN
INFORMATION
V
pF
U
IN
3 3
/RUN pin determines when to
22
V
= 100pF. At maximum input
V
V
D
V
200
V
D
.
D
0 5
kHz
0 5
MAX
C
W
IN
V
V
25
= 12V(nominal),
= 2A. R
–
62
pin. This offset
C
1 58A
mW
0 042
U
SENSE
P-P
2
(refer
can
IN
.
With the 0.05 sense resistor I
increasing the 0.5V Schottky diode dissipation to 0.98W.
C
temperature. C
output ripple. The output ripple in continuous mode will be
highest at the maximum input voltage. The output voltage
ripple due to ESR is approximately:
Step-Down Converter: Duty Cycle Limitations
At high input to output differential voltages the on-time
gets very small. Due to internal gate delays and response
times of the internal circuitry the minimum recommended
on-time is 450ns. Since the LTC1624’s frequency is inter-
nally set to 200kHz a potential duty cycle limitation exists.
When the duty cycle is less than 9%, cycle skipping may
occur which increases the inductor ripple current but does
not cause V
imposes a limit on the input voltage for a given output
voltage only when V
(Remember not to exceed the absolute maximum voltage
of 36V.)
Boost Converter Applications
The LTC1624 is also well-suited to boost converter appli-
cations. A boost converter steps up the input voltage to a
higher voltage as shown in Figure 6.
IN
V
V
is chosen for an RMS current rating of at least 1.0A at
ORIPPLE
IN(MAX)
LTC1624
GND
V
OUT
IN
= 11.1V
= R
SENSE
BOOST
OUT
to lose regulation. Avoiding cycle skipping
SW
ESR
TG
–
Figure 6. Boost Converter
is chosen with an ESR of 0.03 for low
( I
OUT
OUT
L
) = 0.03 (1.58A
+ 5V
C
B
< 2.2V using 30V MOSFETs.
V
IN
R
M1
L1
SC(AVG)
SENSE
For DC > 9%
V
FB
D1
+
= 2A will result,
P-P
R2
R1
LTC1624
C
IN
+
) = 47mV
C
OUT
1624 F06
V
13
OUT
P-P