LTC1872ES6#TRPBF Linear Technology, LTC1872ES6#TRPBF Datasheet - Page 9

• Manufacturer Part Number: LTC1872ES6#TRPBF
• Description: IC DC/DC CONTRLR STEP-UP SOT23-6
• Manufacturer: Linear Technology
• Type: Step-Up (Boost)r

Specifications of LTC1872ES6#TRPBF

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 36 V
• Frequency - Switching: 550kHz
• Voltage - Input: 2.5 ~ 9.8 V
• Operating Temperature: -65°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-6
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -

APPLICATIONS
For most applications, an 80k resistor is suggested for R1.
To prevent stray pickup, locate resistors R1 and R2 close
to LTC1872.
Efficiency Considerations
The efficiency of a switching regulator is equal to the
output power divided by the input power times 100%. It is
often useful to analyze individual losses to determine what
is limiting the efficiency and which change would produce
the most improvement. Efficiency can be expressed as:
where 1, 2, etc. are the individual losses as a percent-
age of input power.
Although all dissipative elements in the circuit produce
losses, four main sources usually account for most of the
losses in LTC1872 circuits: 1) LTC1872 DC bias current,
2) MOSFET gate charge current, 3) I
voltage drop of the output diode.
1. The V
Efficiency = 100% – ( 1 + 2 + 3 + ...)
electrical characteristics, that excludes MOSFET driver
and control currents. V
which increases with V
IN
current is the DC supply current, given in the
U
INFORMATION
IN
U
IN
current results in a small loss
.
W
2
R losses and 4)
U
2. MOSFET gate charge current results from switching
3. I
4. The output diode is a major source of power loss at
5. Transition losses apply to the external MOSFET and
Other losses, including C
losses, and inductor core losses, generally account for
less than 2% total additional loss.
the gate capacitance of the power MOSFET. Each time
a MOSFET gate is switched from low to high to low
again, a packet of charge, dQ, moves from V
ground. The resulting dQ/dt is a current out of V
which is typically much larger than the contoller’s DC
supply current. In continuous mode, I
MOSFET, inductor and current sense resistor. The
MOSFET R
average output current squared can be summed with
I
sense resistor.
high currents. The diode loss is calculated by multiply-
ing the forward voltage by the load current.
increase at higher operating frequencies and input
voltages. Transition losses can be estimated from:
Transition Loss = 2(V
2
2
R losses are predicted from the DC resistances of the
R losses in the inductor ESR in series with the current
DS(ON)
multiplied by duty cycle times the
IN
IN
)
2
I
IN(MAX)
and C
OUT
C
RSS
GATECHG
ESR dissipative
LTC1872
(f)
= f(Qp).
IN
9
to
IN