LTC1515IS8-3.3/5#TRPBF Linear Technology, LTC1515IS8-3.3/5#TRPBF Datasheet - Page 6

• Manufacturer Part Number: LTC1515IS8-3.3/5#TRPBF
• Description: IC MULTI CONFIG 3.3V/5V 8SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Step-Up (Boost), Switched Capacitor (Charge Pump)r

Specifications of LTC1515IS8-3.3/5#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 3.3V, 5V
• Current - Output: 50mA
• Frequency - Switching: 650kHz
• Voltage - Input: 2 ~ 10 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

LTC1515 Series
APPLICATIONS
Output Voltage Selection
The LTC1515-X versions have internal resistor networks
which set the output voltage. The 5/3 pin controls an
internal switch that shorts out a portion of the resistor
network to change the output voltage. A logic high on this
pin produces a 5V output and a low produces either a 3V
output or a 3.3V output.
The output voltage of the LTC1515 is selected using an
external resistor divider (see Figure 1). The output voltage
is determined using the following formula:
The total resistance of R1 and R2 should not exceed 2M,
otherwise excess ripple may appear at V
Maximum V
The maximum output voltage and current available with
the LTC1515 can be calculated based on the effective
output resistance of the charge pump and the open circuit
output voltage. In step-up mode, the open circuit output
voltage is approximately 2V
mode, the open circuit output voltage equals V
relationship between R
in Figure 3.
The following formulas can be used to find the maximum
output voltage that may be programmed using the LTC1515
for a given minimum input voltage and output current
load.
When V
V
mode to step-up mode. In both step-up mode and step-
6
OUT
V
Step-Up Mode: Max V
Step-Down Mode: Max V
OUT
, the part will automatically switch from step-down
IN
= (1.232V)[1 + (R1/R2)]
Figure 1. LTC1515 Output Voltage Selection
– (I
OUT
OUT
and I
)(R
R1
R2
U
OUT
OUT
OUT
1
2
3
4
OUT
INFORMATION
SHDN
POR
FB
GND
) is less than the programmed
and V
Calculations for the LTC1515
U
IN
OUT
= (2)(Min V
LTC1515
(see Figure 2). In step-down
IN
= (Min V
in step-up mode is shown
V
OUT
C1
C1
V
LTC1515 • F01
IN
W
+
–
8
7
6
5
IN
IN
OUT
) – (I
) – (I
.
OUT
OUT
U
)(R
)(R
IN
. The
OUT
OUT
)
)
down mode, R
maximum output current rating can be met.
Capacitor Selection
For best performance, low ESR capacitors are recom-
mended for both C
The C
tantalum and should be 10 F or greater. If the input source
impedance is very low (< 0.5 ) C
Increasing the size of C
output voltage ripple — particularly with high V
(8V or greater). A ceramic capacitor is recommended for
the flying capacitor C1 with a value of 0.1 F or 0.22 F.
Smaller values may be used in low output current
applications.
Output Ripple
Normal LTC1515 series operation produces voltage ripple
on the V
parts to regulate. Low frequency ripple exists due to the
hysteresis in the sense comparator and propagation de-
lays in the charge pump enable/disable circuits. High
frequency ripple is also present mainly from the ESR
IN
Figure 3. Step-Up Mode R
and C
OUT
Figure 2. Step-Up Mode Equivalent Circuit
pin. Output voltage ripple is required for the
40
20
10
30
OUT
0
OUT
1
+
–
capacitors should be either ceramic or
is internally adjusted to ensure that the
IN
R
2V
OUT
and C
IN
2
OUT
I
OUT
INPUT VOLTAGE (V)
V
OUT
+
–
= 20mA
OUT
to 22 F or greater will reduce
I
OUT
3
to reduce noise and ripple.
= 50mA
OUT
C
OUT
IN
vs Input Voltage
4
may not be needed.
LT1515 • F02
LT1515 • F03
I
OUT
5
IN
voltages