TPS62170 / Fsw on the low Vin condition

Hi Kuramochi-san,

TPS62170 enters PS mode as long as the output current is lower than half the inductor's ripple current.

When VIN decreases to typically 15% above VOUT, the TPS6217x does not enter power save mode, regardless of the load current.

The device maintains output regulation in PWM mode.

More information you can find in datasheet:

• 8.4.2 Pulse Width Modulation (PWM) Operation
• 8.4.3 Power Save mode Operation

Regarding variation of the switching frequency see figures: 20 and 21.

More information about frequency variation you can find in this article:

Regards

Lubomir

Hi Kuramochi-san,

The TPS6217x operates with pulse width modulation in continuous conduction mode (CCM) with a nominal switching frequency of about 2.25 MHz. The frequency variation in PWM is controlled and depends on VIN, VOUT and the inductance.

Significant impact on the duty cycle in the customer table has duty cycle:

• Low duty cycle:  The TPS62170 data sheet notes a typical 80-ns absolute minimum on-time that occurs in these cases. This is the primary source of frequency variation at low duty cycles. Fixed propagation delays added to small on-times are another source of variation
• Moderate duty cycle:  Frequency variation in this case is very low because the on- and off-times are not at their extremes.
• High duty cycle: High duty cycles demonstrate a minimum off-time in the topology. Since high duty cycles occur at a lower input voltage and higher output voltage, the energy stored in the inductor during the on-time is lower. This outcome is because there is much less voltage across the inductor. To maximize efficiency, a minimum off-time is included to ensure that sufficient energy is delivered to the output.

Please find more information in the shared documents above.

Best regards

Lubomir Fenic