LTC1174HVCN8 Linear Technology, LTC1174HVCN8 Datasheet - Page 8

• Manufacturer Part Number: LTC1174HVCN8
• Description: IC DC/DC CONV STP-DWN&INVRT 8DIP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Invertingr

Specifications of LTC1174HVCN8

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.25 ~ 18 V
• Current - Output: 1A
• Frequency - Switching: 200kHz
• Voltage - Input: 4 ~ 18.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
Inductor Core Selection
With the value of L selected, the type of inductor must be
chosen. Basically there are two kinds of losses in an
inductor, core and copper
Core losses are dependent on the peak-to-peak ripple
current and the core material. However it is independent of
the physical size of the core. By increasing the inductance
the inductor’s peak-to-peak ripple current will decrease,
therefore reducing core loss. Utilizing low core loss mate-
rial, such as molypermalloy or Kool Mµ will allow users to
concentrate on reducing copper loss and preventing satu-
ration. Figure 1 shows the effect of different core material on
the efficiency of the LTC1174. The CTX core is Kool Mµ and
the CTXP core is powdered iron (material 52).
Although higher inductance reduces core loss, it increases
copper loss as it requires more windings. When space is not
LTC1174
LTC1174-3.3/LTC1174-5
8
Figure 1. Efficiency Using Different Types of
Inductor Core Material
100
100
90
80
70
60
50
90
80
70
60
50
1
1
U
LOAD CURRENT (mA)
LOAD CURRENT (mA)
10
10
U
CTX100-4P
CTX100-4
CTX50-4P
CTX50-4
V
V
I
V
V
I
W
PGM
PGM
100
100
IN
OUT
IN
OUT
= 5V
= 5V
= V
= V
= 3.3V
= 3.3V
IN
IN
1174 F01
500
500
U
a premium larger gauge wire can be used to reduce the wire
resistance. This also prevents excessive heat dissipation.
C
In continuous mode the source current of the P-channel
MOSFET is a square wave of duty cycle V
large voltage transients, a low ESR input capacitor sized for
the maximum RMS current must be used. The C
current is given by:
This formula has a maximum at V
I
because even significant deviations do not offer much relief.
Note that ripple current directly affects capacitor’s lifetime.
DO NOT UNDERSPECIFY THIS COMPONENT. An additional
0.1µF ceramic capacitor is also required on V
frequency decoupling.
C
To avoid overheating, the output capacitor must be sized to
handle the ripple current generated by the inductor. The
worst case RMS ripple current in the output capacitor is
given by:
Although the output voltage ripple is determined by the
hysteresis of the voltage comparator, ESR of the output
capacitor is also a concern. Too high of an ESR will create
a higher ripple output voltage and at the same time cause the
LTC1174 to sleep less often. This will affect the efficiency of
the LTC1174. For a given technology, ESR is a direct
function of the volume of the capacitor. Several small-sized
capacitors can also be paralleled to obtain the same ESR as
one large can. Manufacturers such as Nichicon, Chemicon
and Sprague should be considered for high performance
capacitors. The OS-CON semiconductor dielectric capaci-
tor available from Sanyo has the lowest ESR for its size, at
a higher price.
OUT
IN
OUT
I
I
RMS
RMS
/2. This simple worst case is commonly used for design
=
≈
≈
170
I
I
OUT
PEAK
2
mA
[
V
OUT
or 300mA
(
A
(
RMS
V
V
IN
IN
−
)
V
OUT
IN
)
]
1 2 /
= 2V
OUT
OUT
(
/V
A
, where I
RMS
IN
. To prevent
IN
)
for high
IN
RMS
RMS
1174fe
=