Datasheet

TPS54262-Q1

www.ti.com

SLVS996C –SEPTEMBER 2009–REVISED JUNE 2010

Figure 20. Low Power Mode Figure 21. Low Power Mode (Zoom In)

Any transition from low-power mode to active mode CCM occurs within 5 µs (typical). In low-power mode, the

converter operates as a hysteretic controller with the threshold limits set by VReg_UV (see Equation 10, Figure 4

and Figure 22), for the lower limit and ~V

Reg

for the upper limit. To ensure tight regulation in the low-power mode,

R2 and R3 values are set accordingly (see discussion on Noise Filter on RST_TH and OV_TH Terminals). The

device operates in both automatic (LPM pin is connected to ground) and digitally controlled (status of LPM pin is

controlled by an external device, for example by a microcontroller) low-power mode. The digital low-power mode

can over-ride the automatic low-power mode function by applying the appropriate signal on the LPM terminal.

The part goes into active mode CCM for at least 100 µs, whenever RST_TH or VReg_UV is tripped.

Table 2. LPM Pin Status

LPM PIN STATUS MODES OF OPERATION

Device is forced in normal mode.

At light loads, the device operates in DCM with a switching frequency determined by the

High external resistor connected to RT pin.

At very light loads, the device operates in PSM with a reduced switching frequency (see

Figure 14).

Device automatically changes between normal mode and low-power mode depending on the

Low or open

load current.

Table 3. Modes of Operation

MODES OF OPERATION DESCRIPTION

All circuits including overvoltage threshold circuit (OV_TH) are enabled.

At heavy loads, the device operates in continuous conduction mode irrespective of the status

of LPM pin.

Normal mode (active mode)

At light loads, the device operates in discontinuous conduction mode (DCM) only if LPM pin

is externally set high.

OV_TH circuit is disabled.

Low-power mode

The device is in DCM, and LPM pin should be forced low.

When the device is operating in low-power mode, and if the output is shorted to ground, a reset is asserted. The

thermal shutdown and current limiting circuitry is activated to protect the device. The LPM pin is active low and is

internally pulled down; therefore, the low-power mode is automatically enabled unless this pin is driven high

externally (for example, by a microcontroller) and the device is in continuous conduction mode. However, the

low-power mode operation is initiated only when the device enters discontinuous mode of operation at light

loads, and the LPM pin is low (or connected to ground).

Product Folder Link(s): TPS54262-Q1