LTC1261L Datasheet, PDF (5/12 Pages) Linear Technology – Switched Capacitor Regulated Voltage Inverter

LTC1261L
PIN FUNCTIONS
V_CC (Pin 1): Power Supply. This requires an input voltage
between 2.7V and 5.25V. V_CC must be bypassed to
ground with at least a 1µF capacitor placed in close
proximity to the chip. See the Applications Information
section for details.
C1⁺ (Pin 2): C1 Positive Input. Connect a 0.1µF capacitor
between C1⁺ and C1^–.
C1^– (Pin 3): C1 Negative Input. Connect a 0.1µF capacitor
from C1⁺ to C1^–.
GND (Pin 4): Ground. Connect to a low impedance
ground. A ground plane will help to minimize regulation
errors.
ADJ (COMP for fixed versions) (Pin 5): Output Adjust/
Compensation Pin. For adjustable parts this pin is used
to set the output voltage. The output voltage is divided
down with an external resistor divider and fed back to this
pin to set the regulated output voltage. Typically the
resistor string should draw ≥ 10µA from the output to
minimize errors due to the bias current at the adjust pin.
Fixed output voltage parts have the internal resistor
string connected to this pin inside the package. The pin
can be used to trim the output voltage if desired. It can
also be used as an optional feedback compensation pin to
reduce output ripple on both the adjustable and fixed
output voltage parts. See the Applications Information
section for more information on compensation and out-
put ripple.
OUT (Pin 6): Negative Voltage Output. This pin must be
bypassed to ground with a 1µF or larger capacitor. The
value of the output capacitor and its ESR have a strong
effect on output ripple. See the Applications Information
section for more details.
REG (Pin 7): This is an open-drain output that pulls low
when the output voltage is within 5% of the set value. It
will sink 5mA 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 V_CC and can be
pulled up to 6V above ground without damage.
SHDN (Pin 8): Shutdown. When this pin is at ground the
LTC1261L operates normally. An internal 5µA pull-down
keeps SHDN low if it is left floating. When SHDN is pulled
high, the LTC1261L enters shutdown mode. In shut-
down, the charge pump is disabled, the output collapses
to 0V and the quiescent current drops to 5µA typically.
TEST CIRCUITS
Fixed Output
5V
+
10µF
0.1µF
1 _VCC
SHDN ⁸
2 _C1+
REG ⁷
LTC1261L-X
3 _C1–
OUT ⁶
V_OUT = – 4V (LTC1261L-4)
V_OUT = – 4.5V (LTC1261L-4.5)
4 _{GND COMP} 5 _{+ 3.3µF}
1261L TCO1
Adjustable Output
V_CC
0.1µF
1
V_CC
SHDN ⁸
2 _C1+
REG ⁷
3
LTC1261L
C1^–
OUT
6
4
GND
ADJ ⁵
V_OUT
+ ^3.3µF
1261L TCO2
5