TPS60200, TPS60201, TPS60202, TPS60203

REGULATED 3.3 V, 100-mA LOW-RIPPLE CHARGE PUMP

LOW POWER DC/DC CONVERTERS

SLVS274 – MARCH 2000

5

POST OFFICE BOX 655303

detailed description (continued)

constant-frequency mode

When the output current is higher then the LinSkip current threshold, the charge pump runs continuously at the

the gate drive increases, resulting in a larger voltage across C1 and C2. This regulation scheme minimizes

output ripple. Since the device switches continuously, the output signal contains well-defined frequency

components, and the circuit requires smaller external capacitors for a given output ripple. However,

constant-frequency mode, due to higher operating current, is less efficient at light loads. For this reason, the

device switches seamlessly into the pulse-skip mode when the output current drops below the LinSkip current

threshold.

pulse-skip mode

The regulator enters the pulse-skip mode when the output current is lower than the LinSkip current threshold

of 7 mA. In the pulse-skip mode, the error amplifier disables switching of the power stages when it detects an

output voltage higher than 3.3 V. The controller skips switching cycles until the output voltage drops below 3.3

V. Then the error amplifier reactivates the oscillator and switching of the power stages starts again. A 30 mV

output voltage offset is introduced in this mode.

The pulse-skip regulation mode minimizes operating current because it does not switch continuously and

deactivates all functions except the voltage reference and error amplifier when the output is higher than 3.3 V.

is transferred by the charge pump from the input to the output is limited to the minimum that is necessary to

sustain a regulated output voltage, with the benefit that the output ripple is kept to a minimum. When switching

is disabled from the error amplifier, the load is also isolated from the input.

start up, shutdown, and auto-discharge

During start-up, i.e. when EN is set from logic low to logic high, the output capacitor is directly connected to IN

detects this limit, the converter begins switching. This precharging of the output capacitor guarantees a short

start-up time. In addition, the inrush current into an empty output capacitor is limited. The converter can start

into a full load, which is defined by a 33-

Ω or 66-Ω resistor, respectively.

Driving EN low disables the converter. This disables all internal circuits and reduces the supply current to only

0.05

µA. The device exits shutdown once EN is set high. When the device is disabled, the load is isolated from

the input. This is an important feature in battery operated products because it extends the products shelf life.

Additionally, the output capacitor will automatically be discharged after EN is taken low. This ensures that the

system, when switched off, is in a stable and reliable condition since the supply voltage is removed from the

supply pins.

synchronization to an external clock signal

The operating frequency of the charge pump is limited to 400 kHz in order to avoid interference in the sensitive

455 kHz IF band. The device can either run from the integrated oscillator, or an external clock signal can be used

to drive the charge pump. The maximum frequency of the external clock signal is 800 kHz. The switching

frequency used internally to drive the charge pump power stages is half of the external clock frequency. The

external clock signal is applied to the EN-pin. The device will switch off if the signal on EN is hold low for more

than 10

µs.

When the load current drops below the LinSkip current threshold, the devices will enter the pulse-skip mode

but stay synchronized to the external clock signal.