TPS60120, TPS60121, TPS60122, TPS60123, TPS60124, TPS60125

REGULATED 200-mA HIGH EFFICIENCY CHARGE PUMP

DC/DC CONVERTERS

SLVS257B – NOVEMBER 1999 – REVISED AUGUST 2000

5

POST OFFICE BOX 655303

adaptive mode switching (continued)

the flying capacitors is smaller than half of the supply voltage, then the charge pump switches into the 1.5x

conversion-mode. The charge pump switches back from a 1.5x conversion-mode to a voltage doubler mode

if the load current in 1.5x conversion-mode can no longer be delivered.

than at heavy loads.

The TPS6012x output voltage is regulated using the

ACTIVE-CYCLE regulation. An active cycle controlled

charge pump utilizes two methods to control the output voltage. At high load currents it varies the on resistances

of the internal switches and keeps the ratio ON/OFF time (=frequency) constant. That means the charge pump

runs at a fixed frequency. It also keeps the output voltage ripple as low as in linear-mode. At light loads the

internal resistance and also the amount of energy transferred per pulse is fixed and the charge pump regulates

the voltage by means of a variable ratio of ON-to-OFF time. In this operating point, it runs like a skip mode

controlled charge pump with a very high internal resistance, which also enables a low ripple in this operation

mode. Since the charge pump does effectively switch at lower frequencies at light loads, it achieves a low

quiescent current.

pulse-skip mode

In pulse-skip mode the error amplifier disables switching of the power stages when it detects an output higher

than the nominal output voltage. The oscillator halts and the IC then skips switching cycles until the output

voltage drops below the nominal output voltage. Then the error amplifier reactivates the oscillator and starts

switching the power stages again. The pulse-skip regulation mode minimizes operating current because it does

not switch continuously and deactivates all functions except bandgap reference, error amplifier, and

low-battery/power-good comparator when the output is higher than the nominal output voltage. When switching

is disabled from the error amplifier, the load is also isolated from the input. In pulse-skip mode, a special current

control circuitry limits the peak current. This assures moderate output voltage ripple and also prevents the

device from drawing excessive current spikes out of the battery.

start-up procedure

During start-up, i.e., when ENABLE is set from logic low to logic high, the output capacitor is charged up with

limit, the IC begins switching. This start-up charging of the output capacitor ensures a short start-up time and

eliminates the need of a Schottky diode between IN and OUT. The IC starts into a maximum load resistance

shutdown

Driving ENABLE low places the device in shutdown mode. This disables all switches, the oscillator, and control

logic. The device typically draws 0.05

µA (1 µA max) of supply current in this mode. Leakage current drawn from

the output is as low as 1

µA max. The device exits shutdown once ENABLE is set to a high level. The typical

no-load shutdown exit time is 10

µs. When the device is in shutdown, the load is isolated from the input.

undervoltage lockout and short-circuit current limit

The TPS6012x devices have an undervoltage lockout feature that deactivates the device and places it in

shutdown mode when the input voltage falls below the typical threshold voltage of 1.6 V. During a short-circuit

condition at the output, the current is limited to 115 mA.