The TC1142 generates a regulated negative voltage
from -3V to -5V at 20mA from an input of 2.5V to 5.5V,
using only three external capacitors. Other boost/buck
switching regulators must use an inductor, which is
larger and radiates EMI. An internal voltage
comparator inhibits the charge pump when VOUT is
more negative than the regulated value (per the
ordering option). The values of flying capacitors C1 and
C2 are chosen to be less than COUT in order to reduce
the ripple generated from regulating VOUT in this
manner. The TC1142 also can be used as a -1x buck
regulator by omitting C2, and connecting the C2 pin to
VOUT.
The part goes into shutdown when the CCLK input is
driven low. When in shutdown mode, the part draws a
maximum of 1μA. When CCLK is pulled high, the part
runs from the internal 200kHz oscillator. The device
may be run with an external clock, provided the
frequency is greater than 3kHz and less than 500kHz.
The TC1142 comes in a space-saving MSOP package.