LTC1928-5 LINER [Linear Technology], LTC1928-5 Datasheet - Page 5

• Manufacturer Part Number: LTC1928-5
• Description: Doubler Charge Pump with Low Noise Linear Regulator in ThinSOT
• Manufacturer: LINER [Linear Technology]

V
bypassed with a 2 F low ESR capacitor as close to the
pin as possible for best performance. A minimum capaci-
tance value of 0.1 F is required.
GND (Pin 2): System Ground.
V
should be bypassed with a 2 F low ESR capacitor as
close to the pin as possible for best performance. The V
voltage is internally set to 5V.
APPLICATIONS
PIN
Operation
The LTC1928-5 uses a switched-capacitor charge pump
to generate a CPO voltage of approximately 2V
powers an internal low dropout linear regulator that sup-
plies a regulated output at V
used to sense CPO and V
tioning. The output current is sensed to determine the
charge pump operating mode. A trimmed internal bandgap
is used as the voltage reference and a trimmed internal
oscillator is used to control the charge pump switches.
The charge pump is a doubler configuration that uses one
external flying capacitor. When enabled, a 2-phase
nonoverlapping clock controls the charge pump switches.
At start-up, the LDO is disabled and the load is removed
from CPO. When CPO reaches 1.75V
If CPO falls below 1.45V
erally, the charge pump runs open loop with continuous
clocking for low noise. If CPO is greater than 1.95V
I
Burst Mode operation for increased efficiency but slightly
higher output noise. In Burst Mode operation, the clock is
disabled when CPO reaches 1.95V
CPO droops by about 150mV. The switching frequency is
precisely controlled to ensure that the frequency is above
455kHz and at the optimum rate to ensure maximum effi-
ciency. The switch edge rates are also controlled to mini-
mize noise. The effective output resistance at CPO is
dependent on the voltage at V
value C
pacitor of 2 F should be used at CPO for minimum noise.
OUT
IN
OUT
U
(Pin 1): Input Voltage, 2.7V to 4.4V. V
is less than 200 A, the charge pump will operate in
(Pin 3): Low Noise Regulated Output Voltage. V
FUNCTIONS
FLY
U
and the junction temperature. A low ESR ca-
U
U
IN
INFORMATION
IN
U
the LDO will be disabled. Gen-
OUT
voltages for power-up condi-
IN
. Internal comparators are
, CPO, the flying capacitor
W
IN
IN
the LDO is enabled.
and enabled when
IN
should be
U
IN
IN
. CPO
and
OUT
OUT
CPO (Pin 4): Boosted Unregulated Voltage. Approxi-
mately 1.95V
capacitor.
CP (Pin 5): Flying Capacitor Positive Input.
CN/SHDN (Pin 6): Flying Capacitor Negative Input and
SHDN. When this pin is pulled to ground through a 100
resistor, the part will go into shutdown within approxi-
mately 30 s.
The LDO is used to filter the ripple on CPO and to set an
output voltage independent of CPO. V
internal reference and resistor divider. The LDO requires a
capacitor on V
response. A low ESR capacitor of 2 F should be used.
Maximum I
The maximum available current can be calculated based
on the open circuit CPO voltage, the dropout voltage of the
LDO and the effective output resistance of the charge
pump. The open circuit CPO voltage is approximately 2V
(see Figure 2).
Example:
V
this, calculate V
For minimum noise applications the LDO must be kept out
of dropout to prevent CPO noise from coupling into V
CPO
V
V
R
Maximum unloaded CPO voltage = 2V
V
I
V
OUT(MAX)
IN
OUT
DROPOUT(MAX)
CPO
CPO
must be greater than 1.45V
= 3V
= 5V
= 6V – (30mA • 30 ) = 5.1V
= 30
OUT
= (2V
= (6V – 0.1V – 5V)/30 = 30mA
IN
OUT
at low loads. Bypass with a 2 F low ESR
Calculations
CPO
for stability and improved load transient
IN
= 100mV
:
– V
DROPOUT(MAX)
IN
= 4.35V. To confirm
LTC1928-5
– V
OUT
IN
OUT
= 6V
is set by an
)/R
CPO
OUT
5
IN
.