PM6686TR STMicroelectronics, PM6686TR Datasheet - Page 29

• Manufacturer Part Number: PM6686TR
• Description: IC CTLR DUAL STEP DOWN VFQFPN32
• Manufacturer: STMicroelectronics

Specifications of PM6686TR

• Applications: Controller, Notebook Computers
• Voltage - Input: 5.5 ~ 28 V
• Number Of Outputs: 2
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-VFQFN, 32-VFQFPN
• Output Voltage: 5.5 V
• Output Current: 100 mA
• Output Power: 4.3 mW
• Input Voltage: 5.5 V to 28 V
• Switching Frequency: 33 KHz
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 497-8522-2

PM6686
8.1.4
8.1.5
SKIP
To improve the efficiency at light load the PM6686 implements pulse skip operation mode.
When SKIP pin is tied to GND the inductor current is sensed and if it is equal to zero the
synchronous MOSFET is turned off. As a consequence the output capacitor is left floating
and the discharge depends only on the current sourced by the load. The new T
when the output reaches the voltage regulation. As a consequence at light load conditions
the switching frequency decreases improving the total efficiency of the converter. Working in
discontinuous current mode, the switching and the conduction losses are decreased
skipping some cycles.
If the output load is high enough to make the system work in CCM, skip mode is
automatically changed in PWM mode.
Figure 48.
Non audible SKIP (NA SKIP)
To avoid audio noise the NA SKIP operation mode can be selected, connecting SKIP pin to
VREF2 or leaving it floating. In this condition if a new cycle doesn't start within 30 μ s typ.
from the previous one the PM6686 turns on the low-side MOSFET to discharge the output
capacitor. The inductor current goes negative until the output reaches the voltage regulation
voltage allowing a new cycle to begin. If the switching frequency is above 33 kHz the device
works in SKIP mode.
This operation mode is useful to avoid audio noise but it lowers the efficiency at light loads if
it is compared to the SKIP mode.
Inductor
current
Output
Vreg
T
Inductor current and output voltage in SKIP mode
ON
T
OFF
Doc ID 15281 Rev 4
Device description
ON
starts
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