V (ROOF)

PWROK

V (FLOOR)

OutputVoltage

ChangeInitiated

PWROK

V (FLOOR)

V (ROOF)

OutputVoltage

ChangeInitiated

TPS62650

TPS62651

www.ti.com

SLVS808B

– AUGUST 2009 – REVISED JULY 2011

In PFM mode, when the output voltage is programmed to a lower value by toggling VSEL signal from high to low,

PWROK is defined as low, while the output capacitor is discharged by the load until the converter starts pulsing

to maintain the voltage within regulation. In multiple-step mode, PWROK is defined as low while the output

voltage is ramping up or down.

Figure 49. PWROK Functional Behavior

VOLTAGE RAMP CONTROL

The TPS6265x offers a voltage ramp rate control that can operate in two different modes:

•

Multiple-Step Mode

•

Single-Step Mode

The mode is selected via DEFSLEW control bits in the CONTROL2 register.

Single-Step Voltage Scaling Mode (default), DEFSLEW[2:0] = [111]

In single-step mode, the TPS6265x ramps the output voltage with maximum slew-rate when transitioning

between the floor and the roof voltages (switch to a higher voltage).

When switching between the roof and the floor voltages (transition to a lower voltage), the ramp rate control is

dependent on the mode selection (see CONTROL1 register) associated with the target register (Forced PWM or

auto transition PFM/PWM).

Table 2 shows the ramp rate control when transitioning to a lower voltage with DEFSLEW set to immediate

transition.

Table 2. Ramp Rate Control vs. Target Mode

Mode Associated with Target Voltage

Output Voltage Ramp Rate

Forced PWM

Immediate

DC/DC converter stops switching.

PFM/PWM

Time to ramp down depends on output capacitance and load current

For instance, when the output is programmed to transition to a lower voltage with PFM operation enabled, the

TPS6265x ramps down the output voltage without controlling the ramp rate or having intermediate micro-steps.

The required time to ramp down the voltage depends on the capacitance present at the output of the TPS6265x

and on the load current. From an overall system perspective, this is the most efficient way to perform dynamic

voltage scaling.

Multiple-Step Voltage Scaling Mode, DEFSLEW[2:0] = [000] to [110]

In multiple-step mode the TPS6265x controls the output voltage ramp rate regardless of the load current and

mode of operation (e.g. Forced PWM or PFM/PWM). The voltage ramp control is done by adjusting the time

between the voltage micro-steps.

Copyright

© 2009–2011, Texas Instruments Incorporated

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