LTC1872ES6#TRPBF Linear Technology, LTC1872ES6#TRPBF Datasheet - Page 8

• 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
LTC1872
where f is the operating frequency, C
capacitance and I
tor.
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. The output capacitor RMS current is approxi-
mately equal to:
where I
duty cycle.
When using electrolytic output capacitors, if the ripple and
ESR requirements are met, there is likely to be far more
capacitance than required.
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. An excellent choice of
tantalum capacitors is the AVX TPS and KEMET T510
series of surface mount tantalum capacitors. Also,
ceramic capacitors in X5R pr X7R dielectrics offer excel-
lent performance.
Low Supply Operation
Although the LTC1872 can function down to approxi-
mately 2.0V, the maximum allowable output current is
reduced when V
amount of change as the supply is reduced down to 2V.
Also shown in Figure 3 is the effect of V
goes below 2.3V.
8
I
PK
PK
is the peak inductor current and DC is the switch
DC DC
IN
RIPPLE
decreases below 3V. Figure 3 shows the
2
U
is the ripple current in the induc-
INFORMATION
U
W
OUT
IN
on V
is the output
U
REF
as V
IN
Setting Output Voltage
The LTC1872 develops a 0.8V reference voltage between
the feedback (Pin 3) terminal and ground (see Figure 4). By
selecting resistor R1, a constant current is caused to flow
through R1 and R2 to set the overall output voltage. The
regulated output voltage is determined by:
V
OUT
Figure 3. Line Regulation of V
105
100
0 8
95
90
85
80
75
.
2.0
V
Figure 4. Setting Output Voltage
LTC1872
1
2.2
V
FB
R
R
INPUT VOLTAGE (V)
2
1
3
V
V
2.4
REF
ITH
2.6
R2
R1
REF
2.8
and V
1872 F03
1872 F04
V
OUT
3.0
ITH