LTC1517-5 LINER [Linear Technology], LTC1517-5 Datasheet - Page 5

• Manufacturer Part Number: LTC1517-5
• Description: Micropower, Regulated 5V Charge Pump in a 5-Pin SOT-23 Package
• Manufacturer: LINER [Linear Technology]

APPLICATIONS
Operation
The LTC1517-5 uses a switched-capacitor charge pump
to boost V
achieves regulation by sensing the output voltage through
an internal resistor divider and enabling the charge pump
when the divided output droops below the comparator’s
lower trip point (set by V
enabled, a 2-phase nonoverlapping clock controls the
internal charge pump switches. Flying capacitor C1 is
charged to V
the clock, C1 is stacked in series with V
to V
charging and discharging the flying capacitor occurs at a
free running frequency of 800kHz (typ) and continues until
the divided output voltage reaches the upper trip point of
the comparator. Once the output is back in regulation, the
charge pump is disabled. This method of bursting the
charge pump on and off enables the LTC1517-5 to achieve
high efficiency at extremely low output loads.
Capacitor Selection
For best performance, it is recommended that low ESR
capacitors be used for both C
and ripple. The C
ceramic or tantalum and should be 3.3 F or greater.
Ceramic capacitors will provide the smallest size and
lowest ESR for a given capacitance. If the input source
impedance is very low (< 0.5 ), C
Ceramic capacitors are recommended for the flying ca-
pacitor C1 with values of 0.1 F or 0.22 F. Smaller value
flying capacitors may be used in low I
OUT
through an internal switch. This sequence of
IN
IN
to a 5V 4% regulated output. The part
on phase one of the clock. On phase two of
IN
U
and C
INFORMATION
REF
OUT
U
). When the charge pump is
IN
capacitors should be either
and C
IN
W
may not be needed.
OUT
OUT
IN
to reduce noise
and connected
applications.
U
Output Ripple
Normal LTC1517-5 operation produces voltage ripple on
the V
to regulate. Low frequency ripple exists due to the hyster-
esis in the sense comparator and propagation delays in the
charge pump enable/disable circuits. High frequency ripple
is also present mainly from the ESR (equivalent series
resistance) in the output capacitor. Typical output ripple
with V
with a low ESR (< 0.5 ) 3.3 F output capacitor (minimum
recommended C
exceed 3.3V or for applications requiring < 100mV of
peak-to-peak ripple, a 6.8 F to 10 F C
recommended. Slight further decreases in output ripple
can be achieved by using C
10 F.
Short-Circuit/Thermal Protection
During short-circuit conditions, the LTC1517-5 will draw
between 50mA and 200mA from V
junction temperature. On-chip thermal shutdown circuitry
disables the charge pump once the junction temperature
exceeds approximately 160 C. The charge pump is
reenabled once the junction temperature drops to approxi-
mately 145 C. The LTC1517-5 will cycle in and out of
thermal shutdown indefinitely without latchup or damage
until the V
OUT
IN
= 3V under maximum load is 100mV peak-to-peak
pin. Output voltage ripple is required for the part
OUT
short is removed.
OUT
). For applications requiring V
OUT
capacitors larger than
IN
, causing a rise in
LTC1517-5
OUT
capacitor is
IN
5
to