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POWER SAVE MODE

AUTO DISCHARGE

LOW BATTERY DETECTOR CIRCUIT—LBI/LBO

LOW-EMI SWITCH

LDO

TPS61100, TPS61103

TPS61106, TPS61107

SLVS411B – JUNE 2002 – REVISED APRIL 2004

DETAILED DESCRIPTION (continued)

The SKIPEN pin can be used to select different operation modes. To enable power save, SKIPEN must be set

high. Power save mode is used to improve efficiency at light load. In power save mode the converter only

operates when the output voltage trips below a set threshold voltage. It ramps up the output voltage with one or

several pulses and goes again into power save mode once the output voltage exceeds the set threshold voltage.

This power save mode can be disabled by setting the SKIPEN to GND.

The auto discharge function is needed in applications where the supply voltage of a microcontroller,

microprocessor or memory has to be removed during shutdown in order to make sure that the system quickly

goes in a defined state. The auto discharge function is enabled when the ADEN is set high. It is disabled when

the ADEN is set to GND. When the auto discharge function is enabled, the output capacitor is discharged after

the device is programmed in the shutdown mode. The output capacitor is discharged by an integrated switch of

400

Ω, hence the discharge time depends on the size of the output capacitor.

The low-battery detector circuit is typically used to supervise the battery voltage and to generate an error flag

when the battery voltage drops below a user-set threshold voltage. The function is active only when the device is

enabled. When the device is disabled, both LBO-pin are high-impedance. There are three programmed

thresholds, 400 mV, 450 mV, and 500 mV. The outputs on LBO1 and LBO2 are shown as follows:

LBI INPUT

LBO1

LBO2

(mV)

0-400

0

0

400-450

1

0

450-500

0

1

500-VBAT

1

1

1 means that the output stays at high-impedance and 0 means that the output goes active low. If there is only

one LBO output needed, both outputs can be tied together. Then the switching threshold is at 500 mV at LBI.

The battery voltage, at which the detection circuit switches, can be programmed with a resistive divider

connected to the LBI-pin. The resistive divider scales down the battery voltage to a voltage level of 400 mV

(450 mV, 500 mV), which is then compared to the LBI threshold voltage. The LBI-pin has a built-in hysteresis of

10 mV. See the application section for more details about the programming of the LBI-threshold. If the

low-battery detection circuit is not used, the LBI-pin should be connected to GND (or to VBAT) and the LBO-pin

can be left unconnected. Do not let the LBI-pin float.

The device integrates a circuit that removes the ringing that typically appears on the SW-node when the

converter enters discontinuous current mode. In this case, the current through the inductor ramps to zero and the

rectifying PMOS switch is turned off to prevent a reverse current flowing from the output capacitors back to the

battery. Due to the remaining energy that is stored in parasitic components of the semiconductor and the

inductor, a ringing on the SW-pin is induced. The integrated antiringing switch clamps this voltage to VBAT and

therefore dampens ringing.

The built-in LDO can be used to generate a second output voltage derived from the dc/dc converter output, from

the battery, or from another power source like an ac adapter or a USB power rail. The LDOSENSE input must be

connected to LDOOUT at fixed output voltage versions.

6

Not Recommended for New Designs