TC1142

DS21360B-page 4

 2002 Microchip Technology Inc.

3.0

DETAILED DESCRIPTION

The TC1142 inductorless -2x boost/buck regulator is an

inverting charge pump that uses a pulse-frequency

modulation (PFM) control scheme to produce a

and -5V (depending on the output voltage option) at

20mA maximum load. Output voltage regulation is

achieved by gating ON the clock to the charge pump for

a single half-clock period whenever the output is more

applied to the charge pump has a high frequency

spectral content consisting only of clock harmonics.

When using an external clock, the transient noise is

then synchronized to the clock and is easier to filter in

sensitive applications.

The TC1142 also can be used as a -1x boost/buck

regulator by omitting the C2 capacitor and connecting

The PFM control scheme minimizes supply current at

small loads and permits the use of low value flying

capacitors, which saves on printed circuit board space

and cost. Due to the TC1142’s doubling and inverting

charge pump mechanism, the output voltage is limited

example, a minimum input voltage of 2.5V is required

The CCLK pin of the TC1142 has three functions: It can

select the internal 200kHz oscillator (when held HIGH),

put the TC1142 into shutdown (when held LOW), or

provide an external clock input. To achieve this

functionality, an internal counter is reset by any positive

transition at the CCLK pin, but will time out in typically

160

µsec (i.e., a frequency higher than about 3kHz). If

the counter times out following the last positive

transition, then the internal clock will be gated through

to the charge pump if CCLK is HIGH, or the device will

enter shutdown mode if it is LOW. To enter shutdown,

CCLK must be LOW and the counter must have timed

out. These timing diagrams are shown in Figure 3-4.

A functional circuit diagram of the TC1142 is shown in

on-chip reference voltage, and the comparator output

is used to gate the charge pump clock. The charge

pump is a negative voltage doubler and has two

phases of operation which are further illustrated in

Figure 3-2 and Figure 3-3. In phase 1, shown in

Figure 3-2, the flying capacitor C1 charges the flying

capacitor C2 while the device load is totally serviced by

phase 2, shown in Figure 3-3, the capacitor C1 is

In normal operation, the TC1142 charge pump stays in

phase 2 and only switches to phase 1 as required to

maintain output voltage regulation.

FIGURE 3-1:

FUNCTIONAL CIRCUIT DIAGRAM

C1+

C1–

C2+

C2–

+

+

–

1.2V

+

Clock

Circuit

OSC

Override

Shutdown