The TC1121 is a charge pump converter with 100 mA
output current capability. It converts a 2.4V to 5.5V
input to a corresponding negative output voltage. As
with all charge pump converters, the TC1121 uses no
inductors saving cost, size and EMI.
An on-board oscillator operates at a typical frequency
of 10 kHz (at V+ = 5V) when the frequency control input
(FC) is connected to ground. The oscillator frequency
increases to 200 kHz when FC is connected to V+,
allowing the use of smaller capacitors. Operation at
sub-10 kHz frequencies results in lower quiescent
NScurrent and is accomplished with the addition of an
external capacitor from OSC (pin 7) to ground. The
TC1121 also can be driven from an external clock
NSconnected OSC. Typical supply current at 10 kHz is
50 μA, and falls to less than 1 μA when the shutdown
input is brought low, whether the internal or an external
clock is used. The TC1121 is available in 8-pin SOIC,
MSOP and PDIP packages.