LTC1772BES6#TRPBF Linear Technology, LTC1772BES6#TRPBF Datasheet - Page 10

• Manufacturer Part Number: LTC1772BES6#TRPBF
• Description: IC CTRLR DC/DC S-DWN SOT23-6
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1772BES6#TRPBF

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 9.8 V
• Current - Output: 1A
• Frequency - Switching: 550kHz
• Voltage - Input: 2.5 ~ 9.8 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: TSOT-23-6, TSOT-6
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
LTC1772B
size or height requirements in the design. Due to the high
operating frequency of the LTC1772B, ceramic capacitors
can also be used for C
if there is any question.
The selection of C
series resistance (ESR). Typically, once the ESR require-
ment is satisfi ed, the capacitance is adequate for fi ltering.
The output ripple (ΔV
where f is the operating frequency, C
capacitance and I
tor. The output ripple is highest at maximum input voltage
since ΔI
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 somewhat higher
price. Once the ESR requirement for C
the RMS current rating generally far exceeds the I
requirement.
Low Supply Operation
Although the LTC1772B can function down to approxi-
mately 2.0V, the maximum allowable output current is
reduced when V
the amount of change as the supply is reduced down to
2V. Also shown in Figure 4 is the effect of V
V
Setting Output Voltage
The regulated output voltage is determined by:
For most applications, an 80k resistor is suggested for
R1. To prevent stray pickup, locate resistors R1 and R2
close to LTC1772B.
10
IN
V
goes below 2.3V.
OUT
V
OUT
L
= 0.8 1+
increases with input voltage.
I
RIPPLE
IN
RIPPLE
R2
OUT
R1
decreases below 3V. Figure 4 shows
ESR +
IN
OUT
is driven by the required effective
. Always consult the manufacturer
is the ripple current in the induc-
) is approximated by:
4fC
1
OUT
OUT
OUT
has been met,
is the output
IN
on V
RIPPLE(P-P)
REF
as
Effi ciency Considerations
The effi ciency 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 effi ciency and which change would produce
the most improvement. Effi ciency can be expressed as:
where η1, η2, 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 LTC1772B circuits: 1) LTC1772B DC bias
Effi ciency = 100% – (η1 + η2 + η3 + ...)
Figure 4. Line Regulation of V
105
100
95
90
85
80
75
LTC1772B
Figure 5. Setting Output Voltage
2.0
V
FB
2.2
3
INPUT VOLTAGE (V)
V
V
2.4
REF
ITH
2.6
R2
R1
REF
2.8
and V
1772 F04
V
OUT
1772 F03
3.0
ITH
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