Datasheet

5
LTC1515 Series
PIN FUNCTIONS
UUU
C1
+
(Pin 6): Charge Pump Flying Capacitor, Positive
Terminal.
V
IN
(Pin 7): Charge Pump Input Voltage. May be between
2V and 10V. V
IN
should be bypassed with a ≥ 10µF low
ESR capacitor as close as possible to the pin for best
performance.
V
OUT
(Pin 8): Regulated Output Voltage. Pin selectable to
either 3V/5V, 3.3V/5V or adjustable using an external
resistor divider (LTC1515). V
OUT
should be bypassed with
a ≥ 10µF low ESR capacitor as close as possible to the pin
for best performance.
BLOCK DIGRAM
WW
SI PLIFIED
APPLICATIONS INFORMATION
WUU
U
Regulator Operation
The regulator section of the LTC1515, LTC1515-3/5 and
LTC1515-3.3/5 consists of a charge pump, reference,
comparator and some logic. The divided down output
voltage is compared to the internal reference voltage.
When the divided output drops below the reference volt-
age, the charge pump is enabled, which boosts the output
back into regulation. Hysteresis in the comparator forces
the regulator to burst on and off and causes approximately
100mV of peak-to-peak ripple to appear at the output. By
enabling the charge pump only when needed, the parts
achieve high efficiencies with low output load currents.
Each part’s charge pump has a unique architecture that
allows the input voltage to be either stepped up or stepped
down to produce a regulated output. Internal circuitry
senses the V
IN
to V
OUT
differential voltage and controls the
charge pump operating mode. In addition, the effective
output impedance of the charge pump is internally
adjusted to prevent large inrush currents and allow for a
wide input voltage range. When the input voltage is lower
than the output voltage, the charge pump operates as a
step-up voltage doubler. When the input voltage is greater
than the output, the charge pump operates as a step-down
gated switch.
+
–
+
–
V
OS
1.232V
V
REF
650kHz
OSCILLATOR
RESET
COUNTER
STEP-UP/STEP-DOWN
CHARGE PUMP
V
IN
SHDN
POR
GND
C1
–
C1
+
V
OUT
(LTC1515-X)
(LTC1515-X)
LTC1515 • BD
FB
(LTC1515)
5/3
(LTC1515-X)
EN
EN