LTC1514-3.3/LTC1514-5
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PIN FUNCTIONS
battery comparator and 1.145V reference are kept alive in
shutdown.
VIN (Pin 7): Charge Pump Input Voltage. May be between
2V and 8V (LTC1514-3.3) or between 2.7V and 10V
(LTC1514-5). VIN should be bypassed with a ≥10µF low
ESR capacitor as close as possible to the pin for best
performance.
GND (Pin 4): Ground. Should be tied to a ground plane for
best performance.
C1– (Pin 5): Charge Pump Flying Capacitor, Negative
Terminal.
C1+ (Pin 6): Charge Pump Flying Capacitor, Positive
Terminal.
VOUT (Pin 8): Regulated Output Voltage. The output volt-
age is internally set to either 3.3V (LTC1514-3.3) or to 5V
(LTC1514-5)usinganinternalresistordivider.VOUT should
be bypassed with a ≥10µF low ESR capacitor as close as
possible to the pin for best performance.
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APPLICATIONS INFORMATION
Regulator Operation
tantalum and should be 10µF or greater. If the input
source impedance is very low (<0.5Ω), CIN may not be
needed.IncreasingthesizeofCOUT to22µForgreaterwill
reduce output voltage ripple—particularly with high VIN
voltages (8V or greater). A ceramic capacitor is recom-
mended for the flying capacitor C1 with a value of 0.1µF
or 0.22µF. Smaller value flying capacitors may be used in
low output current applications.
The regulator section of the LTC1514-3.3/LTC1514-5
consists of a charge pump, reference, comparator and
some logic. The divided down output voltage is com-
pared to the internal reference voltage. When the divided
output drops below the reference voltage, the charge
pump is enabled, which boosts the output back into
regulation. Hysteresis in the comparator forces the regu-
lator 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
LTC1514-3.3 and LTC1514-5 are able to achieve high
efficiencies with low output load currents.
Output Ripple
Normal LTC1514-3.3/LTC1514-5 operation produces
voltage ripple on the VOUT pin. Output voltage ripple is
required for the parts to regulate. Low frequency ripple
exists due to the hysteresis 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 (VIN < 8V) under maxi-
mumloadis100mVpeak-to-peakwithalowESR(<0.5Ω)
10µF output capacitor. For applications requiring VIN to
exceed 8V, a 22µF or larger COUT capacitor is recom-
mended to maintain max ripple in the 100mV range.
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 VIN to VOUT 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
voltageislowerthantheoutputvoltage, thechargepump
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.
The magnitude of the ripple voltage depends on several
factors. High input voltages increase the output ripple
since more charge is delivered to COUT per charging
cycle. A large C1 flying capacitor (>0.22µF) also
increases ripple in step-up mode for the same reason.
Largeoutputcurrentloadand/orasmalloutputcapacitor
(<10µF) results in higher ripple due to higher output
voltage dV/dt. High ESR capacitors (ESR > 0.5Ω) on the
Capacitor Selection
For best performance, low ESR capacitors are recom-
mendedforbothCIN andCOUT toreducenoiseandripple.
The CIN and COUT capacitors should be either ceramic or
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Linear [ Linear ]
