LTC1515IS8-3/5#PBF Linear Technology, LTC1515IS8-3/5#PBF Datasheet - Page 7

• Manufacturer Part Number: LTC1515IS8-3/5#PBF
• Description: IC MULTI CONFIG 3V/5V 50MA 8SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Step-Up (Boost), Switched Capacitor (Charge Pump)r

Specifications of LTC1515IS8-3/5#PBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 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: -

APPLICATIONS
(equivalent series resistance) in the output capacitor.
Typical output ripple (V
100mV peak-to-peak with a low ESR, 10 F output capaci-
tor. For applications requiring V
larger C
mum ripple in the 100mV range.
The magnitude of the ripple voltage depends on several
factors. High input voltages increase the output ripple
since more charge is delivered to C
A large C1 flying capacitor (> 0.22 F) also increases ripple
in step-up mode for the same reason. Large output
current load and/or a small output capacitor (<10 F)
results in higher ripple due to higher output voltage dV/dt.
High ESR capacitors (ESR > 0.5 ) on the output pin cause
high frequency voltage spikes on V
cycle.
There are several ways to reduce the output voltage ripple.
A large C
the low and high frequency ripple due to the lower C
charging and discharging dV/dt and the lower ESR typi-
cally found with higher value (larger case size) capacitors.
A low ESR (<0.5 ) ceramic output capacitor will mini-
mize the high frequency ripple, but will not reduce the low
frequency ripple unless a high capacitance value is cho-
sen. A reasonable compromise is to use a 10 F to 22 F
tantalum capacitor in parallel with a 1 F to 3.3 F ceramic
capacitor on V
frequency ripple. An RC or LC filter may also be used to
reduce high frequency voltage spikes (see Figure 4).
Inrush Currents
A common problem with switched capacitor regulators is
inrush current—particularly during power-up and com-
OUT
Figure 4. Output Ripple Reduction Techniques
OUT
capacitor is recommended to maintain maxi-
LTC1515-X
LTC1515-X
LTC1515/
LTC1515/
capacitor (22 F or greater) will reduce both
V
V
OUT
OUT
OUT
8
8
U
to reduce both the low and high
+
+
IN
INFORMATION
15 F
TANTALUM
10 F
TANTALUM
U
< 8V) under maximum load is
2
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
IN
to exceed 8V, a 22 F or
OUT
+
W
OUT
per charging cycle.
1 F
CERAMIC
10 F
TANTALUM
with every clock
V
V
OUT
OUT
LT1515 • F04
U
OUT
ing out of shutdown mode. Whenever large V
V
pumps will pull large current spikes from the input supply.
Only the effective charge pump output impedance limits
the current while the charge pump is enabled. This may
disrupt input supply regulation, especially if the input
supply is a low power DC/DC converter or linear regulator.
The LTC1515 family minimizes inrush currents both at
start-up and under high V
Internal soft start circuitry controls the rate at which V
may be charged from 0V to its final regulated value. The
typical start-up time from V
corresponds to an effective V
12.5mA for a 10 F output capacitor (27.5mA for 22 F,
etc.). Note that any output current load present during
start-up will add directly to the charging currents men-
tioned above. The soft start circuitry limits start-up cur-
rent both at initial power-up and when coming out of
shutdown.
As the V
grows, the effective output impedance of the charge pump
is automatically increased by internal voltage sensing
circuitry. This feature minimizes the current spikes pulled
from V
to reduce both input and output ripple.
Power-On Reset
The POR pin is an open-drain output that pulls low when
the output voltage is out of regulation. When the V
rises to within 6.5% of regulation, an internal timer is
started which releases POR after 200ms (typ). In shut-
down, the POR output is pulled low. In normal operation,
an external pull-up resistor is generally used between the
POR pin and V
Protection Features
All of the parts contain thermal shutdown and short-
circuit protection features. The parts will shut down when
the junction temperature reaches approximately 150 C
and will resume operation once the junction temperature
has dropped back to approximately 140 C. The parts will
limit output current to 12mA (typ) when a short circuit
condition (V
indefinite short to GND.
IN
) to V
IN
OUT
IN
whenever the charge pump is enabled and helps
(or boosted V
OUT
voltage differentials are present, most charge
OUT
< 100mV) exists. The parts can survive an
.
IN
IN
) to V
OUT
to V
OUT
LTC1515 Series
= 0V to 5V is 4ms. This
OUT
charging current of only
OUT
operation.
voltage differential
IN
(or boosted
7
OUT
OUT