Datasheet

1
LTC1550L/LTC1551L
Low Noise, Switched
Capacitor Regulated
Voltage Inverters
The LTC
®
1550L/LTC1551L are switched capacitor charge
pump voltage inverters which include internal linear post-
regulators to minimize output ripple. The LTC1550L fixed
output voltage versions include –4.1V, –2.5V and –2V with
ripple voltages typically below 1mV
P-P
. The LTC1550L is
also available in an adjustable output voltage version. The
LTC1550L/LTC1551L are ideal for use as bias voltage
generators for GaAs transmitter FETs in portable RF and
cellular telephone applications.
The LTC1550L/LTC1551L operate from single 2.7V to
5.5V supplies and draw typical quiescent currents of
3.5mA with a 5V supply. Each device includes a TTL
compatible Shutdown pin which drops supply current to
0.2µA typically. The LTC1550L Shutdown pin is active low
(SHDN), while the LTC1551L 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 LTC1550L/LTC1551L require two additional re-
sistors to set the output voltage. The LTC1550L/LTC1551L
will supply up to 20mA (depending on V
CC
to V
OUT
range),
while maintaining guaranteed output regulation of ±2.5%.
Both fixed voltage and adjustable LTC1550L/LTC1551L
are available in 8-lead MSOP and SO plastic packages: the
adjustable LTC1550L is also available in a 16-pin SSOP
with the REG pin.
, LTC and LT are registered trademarks of Linear Technology Corporation.
5µs/DIV 1550L/51L TA01a
Regulated Negative Voltage from a Single
Positive Supply
Low Output Ripple: Less Than 1mV
P-P
Typ
High Charge Pump Frequency: 900kHz
Small Charge Pump Capacitors: 0.1µF
Requires Only Four External Capacitors
Fixed –4.1V, –2.5V, –2V or Adjustable Output
Shutdown Mode Drops Supply Current to <1µA
High Output Current: Up to 20mA (Depending on
V
CC
to V
OUT
Range)
Output Regulation: 2.5% Over Line, Load and
Temperature
Available in 8-Lead MSOP, 8-Lead Narrow SO and
16-Lead Narrow SSOP
GaAs FET Bias Generators
Negative Supply Generators
Battery-Powered Systems
Single Supply Applications
V
OUT
AC COUPLED
2mV/DIV
V
OUT
Output Noise and Ripple
Figure 1. –2V Generator with 1mV
P-P
Noise
1
2
3.6V
8
7
REG
CP
OUT
SHDN
V
CC
C1
+
V
OUT
LTC1550L-2
GND
C1
C
OUT
10µF
1550L/51L TA01
V
OUT
= –2V
I
LOAD
= 5mA
C
CP
0.1µF
R1
10k
POWER VALID
C1
0.1µF
2.2µF
C
IN
3
4
6
5
C
L
0.1µF
+
+
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
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