LTC1874EGN Linear Technology, LTC1874EGN Datasheet - Page 9

• Manufacturer Part Number: LTC1874EGN
• Description: IC CTRLR DC/DC DUAL STPDN 16SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1874EGN

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 2
• Voltage - Output: 0.8 ~ 9.8 V
• Frequency - Switching: 550kHz
• Voltage - Input: 2.5 ~ 9.8 V
• Operating Temperature: -65°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Output: -
• Power - Output: -

APPLICATIO S I FOR ATIO
short-circuited. Under this condition the diode must safely
handle I
important to adequately specify the diode peak current and
average power dissipation so as not to exceed the diode
ratings.
Under normal load conditions, the average current con-
ducted by the diode is:
The allowable forward voltage drop in the diode is calcu-
lated from the maximum short-circuit current as:
where P
determined by efficiency and/or thermal requirements.
Schottky diodes are a good choice for low forward drop
and fast switching times. Remember to keep lead length
short and observe proper grounding (see Board Layout
Checklist) to avoid ringing and increased dissipation.
C
In continuous mode, the source current of the P-channel
MOSFET is a square wave of duty cycle (V
(V
input capacitor sized for the maximum RMS current must
be used. The maximum RMS capacitor current is given by:
IN
IN
I
V
C
D
and C
F
+ V
IN
Required I
D
PEAK
I
D
SC MAX
). To prevent large voltage transients, a low ESR
V
OUT
is the allowable power dissipation and will be
IN
V
P
(
IN
D
at close to 100% duty cycle. Therefore, it is
Selection
V
V
OUT
)
D
RMS
U
I
OUT
I
MAX
U
V
OUT
W
V
IN
V
IN
V
OUT
OUT
U
1 2 /
+ V
D
)/
This formula has a maximum at V
= I
used for design because even significant deviations do not
offer much relief. Several capacitors may be paralleled to
meet the size or height requirements in the design. Due to
the high operating frequency of the controller, ceramic
capacitors can also be used for C
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 is the operating frequency, C
capacitance and I
tor. The output ripple is highest at maximum input voltage
since I
Once the ESR requirement for C
RMS current rating generally far exceeds the I
requirement. Multiple capacitors may have to be paral-
leled to meet the ESR or RMS current handling require-
ments of the application. Aluminum electrolytic and dry
tantalum capacitors are both available in surface mount
configurations. An excellent choice of tantalum capacitors
are the AVX TPS and KEMET T510 series of surface mount
tantalum capacitors.
OUT
V
OUT
/2. This simple worst-case condition is commonly
L
increases with input voltage.
I
RIPPLE
RIPPLE
OUT
ESR
OUT
is driven by the required effective
is the ripple current in the induc-
) is approximated by:
4
fC
1
OUT
IN
OUT
IN
= 2V
. Always consult the
has been met, the
OUT
OUT
LTC1874
is the output
, where I
RIPPLE(P-P)
RMS
9