LTC1550/LTC1551
Low Noise, Switched
Capacitor Regulated
Voltage Inverters
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DESCRIPTION
FEATURES
The LTC®1550/LTC1551 are switched capacitor charge
pump voltage inverters which include internal linear postregulators to minimize output ripple. Output voltages are
fixed at – 4.1V, with ripple voltages typically below 1mVP-P.
The LTC1550 is also available in an adjustable output
voltage version. The LTC1550/LTC1551 are ideal for use
as bias voltage generators for GaAs transmitter FETs in
portable RF and cellular telephone applications.
Regulated Negative Voltage from a Single
Positive Supply
Low Output Ripple: Less Than 1mVP-P Typ
High Charge Pump Frequency: 900kHz Typ
Small Charge Pump Capacitors: 0.1µF
Requires Only Four External Capacitors
Fixed – 4.1V or Adjustable Output
Shutdown Mode Drops Supply Current to < 1µA
High Output Current: Up to 10mA, VCC = 5V
Output Regulation: 5%
Available in SO-8 and 16-Lead SSOP
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The LTC1550/LTC1551 operate from single 4.5V to 6.5V
supplies and draw typical quiescent currents of 4.25mA
with a 5V supply. Each device includes a TTL compatible
Shutdown pin which drops supply current to 0.2µA typically. The LTC1550 Shutdown pin is active low (SHDN),
while the LTC1551 Shutdown pin is active high (SHDN).
Only four external components are required: an input bypass
capacitor, two 0.1µF charge pump capacitors and a filter
capacitor at the linear regulator output. The adjustable LTC1550
requires two additional resistors to set the output voltage. The
LTC1550/LTC1551 will supply up to 10mA output current
with a 5V supply, while maintaining guaranteed output
regulation of ±5%.
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APPLICATIONS
GaAs FET Bias Generators
Negative Supply Generators
Battery-Powered Systems
Single Supply Applications
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The fixed voltage LTC1550/LTC1551 are available in S0-8
plastic packages. The adjustable LTC1550 is available in a
16-pin SSOP.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATION
– 4.1V Generator with 1mVP-P Noise
1
2
+
4.7µF
CIN
SHDN
SENSE
VCC
CPOUT
8
7
CCP
0.1µF
LTC1551
3
4
C1+
GND
VOUT
C1 –
6
FERRITE BEAD
C1
0.1µF
VOUT
AC COUPLED
2mV/DIV
5
+
VCC
VOUT Output Noise and Ripple
COUT
10µF
VOUT = –4.1V
ILOAD = 5mA
CL
0.1µF
1550/51 F01
10µs/DIV
1550/51 TA02
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