LTC1550 Просмотр технического описания (PDF) - Linear Technology
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LTC1550 Datasheet PDF : 12 Pages
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LTC1550/LTC1551
PIN FUNCTIONS
REG: This is an open-drain output that pulls low when the
output voltage is within 5% of the set value. It will sink 7mA
to ground with a 5V supply. The external circuitry must
provide a pull-up or REG will not swing high. The voltage
at REG may exceed VCC and can be pulled up to 12V above
ground without damage.
ADJ: For adjustable versions only, this is the feedback
point for the external resistor divider string. Connect a
divider string from AGND to VOUT with the divided tap
connected to ADJ. Note that the resistor string needs to be
connected “upside-down” from a traditional negative regu-
lator. See the Applications Information section for hook-
up details.
NC: No Internal Connection.
BLOCK DIAGRAM
CCP
VCC
CPOUT
COUT
CLK
900kHz
S1
S4
C1+
C1
S2
C1–
LINEAR
REGULATOR
–+
S3
CHARGE
PUMP
*SHDN
*SHDN FOR LTC1550, SHDN FOR LTC1551
** FIXED OUTPUT VERSIONS ONLY
60mV
1.24V
1.18V
SENSE
**
**
+
COMP2
–
VOUT
ADJ
REG
1550/51 BD
APPLICATIONS INFORMATION
OVERVIEW
The LTC1550/LTC1551 are switched capacitor, inverting
charge pumps with internal linear post-regulators. The
LTC1550CS8/LTC1551CS8 provide a regulated, low ripple
– 4.1V output at up to 10mA load current from a single 5V
supply. The LTC1550CGN provides a regulated, low ripple
adjustable output. Output load current for the adjustable
version depends on the input/output voltage combination.
Consult the graph provided in the Typical Performance
Characteristics section and the Electrical Characteristics
table for guaranteed test points. The LTC1550/LTC1551
are ideal for use as bias voltage generators for GaAs
transmitter FETs in portable RF and cellular telephone
applications. The LTC1550 features an active-low
Shutdown pin (SHDN) that drops quiescent current to
below 1µA. The LTC1551 is identical to the LTC1550,
6
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