Standard 555 Micropower
The CSS555 is pin-for-pin compatible with the
customary 555 series timers as Figure 1 indicates.
Therefore, application circuits have the familiar 555
topology as, for example, in the astable circuit illustrated
in Figure 2.
However, the micropower nature of this IC allows
using external components with values that demand much
less power. For example, the LED blinker in the electronic
paperweight in Figure 3 uses the above astable circuit
with timing resistors RA = 10M, RB = 47K, and a 0.22 µF
timing capacitor. It blinks perpetually on the energy stored
in a 1F capacitor charged from a small photovoltaic cell
taking in typical desktop lighting.
Another application of the CSS555 in the standard
(unprogrammed) mode is the solar engine shown in
Figure 4. Here, the circuit is a sort of monostable
arrangement with a more or less constant voltage (about
1.4V usually) on the trigger and threshold pins, which is
supplied by a photodiode (a suitable LED, actually). The
supply voltage to the circuit varies as the storage capacitor
Cs charge from a solar cell, or discharge through the load
when the output pin goes high.
It goes high when the supply reaches three times the
trigger voltage, and goes low when the supply drops to
1.5 times the photodiode voltage.
The original concept for this solar engine circuit was
devised by Manfred Schaffran and Wilf Rigter in 2003
when only the 7555 timer was available. The CSS555
greatly improves the efficiency since the circuit now takes
under 5 µA during periods when the storage capacitor is
charging up. The various available 7555s required
anywhere from 50 µA to 180 µA. A CSS555 equipped
solar engine has operated perfectly from a tiny solar cell
supplying a mere 15 µA.
The little robot “Walker” in Figure 5 is equipped with
this circuit, a good size solar cell atop his head, and,
presently, a 0.22F capacitor. He periodically waddles
around in a little circle (one of his arms/legs is longer than
the other) whenever he has gleaned enough energy from
The CSS555 is a micropower
programmable version of the 555
family of timer ICs. It operates at a
current under 5 μA and a supply
voltage from 5.5V down to 1.2V.
These qualities make it particularly
well-suited for long lasting battery
and small solar powered projects.
It can be used in standard 555
configurations as supplied, but it is
also user programmable to
produce extended timing periods.
By James Senft (a.k.a., TinkerJim)
34 February 2016
FIGURE 1. The CSS555 has the same pinout.
FIGURE 2. Astable circuit diagram. Note that the reset
pin must be held high for the chip to be active.