LTC1624CS8 Linear Technology, LTC1624CS8 Datasheet - Page 9

• 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: -

monly used for design because even significant deviations
do not offer much relief. Note that capacitor manufacturer’s
ripple current ratings are often based on only 2000 hours
of life. This makes it advisable to further derate the
capacitor, or to choose a capacitor rated at a higher
temperature than required. Several capacitors may also be
paralleled to meet size or height requirements in the
design. Always consult the manufacturer if there is any
question.
The selection of C
series resistance (ESR). Typically, once the ESR require-
ment is satisfied the capacitance is adequate for filtering.
The output ripple ( V
where f = operating frequency, C
and I
is highest at maximum input voltage since I
with input voltage. With I
ripple will be less than 100mV at maximum V
Manufacturers such as Nichicon, United Chemicon and
SANYO should be considered for high performance
through-hole capacitors. The OS-CON semiconductor
dielectric capacitor available from SANYO has the lowest
ESR(size) product of any aluminum electrolytic at a some-
what higher price. Once the ESR requirement for C
been met, the RMS current rating generally far exceeds
the I
In surface mount applications multiple capacitors may
have to be paralleled to meet the ESR or RMS current
handling requirements of the application. Aluminum elec-
trolytic and dry tantalum capacitors are both available in
surface mount configurations. In the case of tantalum it is
critical that the capacitors are surge tested for use in
switching power supplies. An excellent choice is the AVX
TPS series of surface mount tantalums, available in case
heights ranging from 2mm to 4mm. Other capacitor types
include SANYO OS-CON, Nichicon WF series and Sprague
595D series and the new ceramics. Ceramic capacitors are
now available in extremely low ESR and high ripple current
APPLICATIONS
C
OUT
RIPPLE(P-P)
V
OUT
L
= ripple current in the inductor. The output ripple
Required ESR < 2R
I ESR
L
requirement.
OUT
U
OUT
is driven by the required effective
4
INFORMATION
) is determined by:
fC
U
1
SENSE
OUT
L
= 0.4I
OUT
W
= output capacitance
OUT(MAX)
IN
, assuming:
L
the output
U
increases
OUT
has
ratings that are ideal for input capacitor applications.
Consult the manufacturer for other specific recommend-
ations.
INTV
An internal regulator produces the 5V supply that powers
the drivers and internal circuitry within the LTC1624.
Good V
transient currents required by the MOSFET gate drivers.
High input voltage applications in which large MOSFETs
are being driven at high frequencies may cause the maxi-
mum junction temperature rating for the LTC1624 to be
exceeded. The supply current is dominated by the gate
charge supply current as discussed in the Efficiency
Considerations section. The junction temperature can be
estimated by using the equations given in Note 1 of the
Electrical Characteristics table. For example, the LTC1624
is limited to less than 17mA from a 30V supply:
To prevent maximum junction temperature from being
exceeded, the input supply current must be checked
operating in continuous mode at maximum V
Step-Down Converter: Topside MOSFET Driver
Supply (C
An external bootstrap capacitor C
pin supplies the gate drive voltage for the topside MOSFET.
Capacitor C
internal diode D
When the topside MOSFET is to be turned on, the driver
places the C
MOSFET. This enhances the MOSFET and turns on the
topside switch. The switch node voltage SW rises to V
and the BOOST pin rises to V
boost capacitor C
total input capacitance of the topside MOSFET. In most
applications 0.1 F is adequate.
Significant efficiency gains can be realized by supplying
topside driver operating voltage from the output, since the
V
will be scaled by a factor of (Duty Cycle)/(Efficiency). For
5V regulators this simply means connecting the BOOST
IN
T
current resulting from the driver and control currents
J
CC
= 70 C + (17mA)(30V)(110 C/W) = 126 C
Regulator
IN
B
bypassing is necessary to supply the high
, D
B
B
in the functional diagram is charged through
B
voltage across the gate to source of the
)
B
B
from INTV
needs to be 50 times greater than the
IN
CC
+ INTV
when the SW pin is low.
B
connected to the BOOST
CC
. The value of the
LTC1624
IN
.
9
IN