ADP3168 Analog Devices, ADP3168 Datasheet - Page 12

• Manufacturer Part Number: ADP3168
• Description: 4-Phase Synchronous Buck Controller
• Manufacturer: Analog Devices

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ADP3168
DYNAMIC VID
The ADP3168 incorporates the ability to dynamically change
the VID input while the controller is running. This allows the
output voltage to change while the supply is running and
supplying current to the load. This is commonly referred to as
VID on-the-fly (OTF). A VID OTF can occur under either light
load or heavy load conditions. The processor signals the
controller by changing the VID inputs in multiple steps from
the start code to the finish code. This change can be either
positive or negative.
When a VID input changes state, the ADP3168 detects the
change and ignores the DAC inputs for a minimum of 400 ns.
This prevents a false code due to logic skew while the six VID
inputs are changing. Additionally, the first VID change initiates
the PWRGD and CROWBAR blanking functions for a mini-
mum of 250 µs to prevent a false PWRGD or CROWBAR event.
Each VID change resets the internal timer. Figure 10 shows VID
on-the-fly performance when the output voltage is stepping up
and the output current is switching between minimum and
maximum values, which is the worst-case situation.
POWER-GOOD MONITORING
The Power-Good comparator monitors the output voltage via
the CSREF pin. The PWRGD pin is an open-drain output
whose high level (when connected to a pull-up resistor)
indicates that the output voltage is within the nominal limits
specified in Table 1 based on the VID voltage setting. PWRGD
goes low if the output voltage is outside of this specified range.
PWRGD is blanked during a VID OTF event for a period of
250 µs to prevent false signals during the time the output is
changing.
VID Change = 5 mV, 5 µs per Step, 50 Steps, I
4
Figure 10. VID On-the-Fly Waveforms, Circuit of Figure 12.
OUT
Change =5 A to 65 A
Rev. B | Page 12 of 24
OUTPUT CROWBAR
As part of the protection for the load and output components of
the supply, the PWM outputs are driven low (turning on the
low-side MOSFETs) when the output voltage exceeds the upper
Power-Good threshold. This crowbar action stops once the
output voltage has fallen below the release threshold of
approximately 450 mV.
Turning on the low-side MOSFETs pulls down the output as the
reverse current builds up in the inductors. If the output over-
voltage is due to a short of the high-side MOSFET, this action
current limits the input supply or blows its fuse, protecting the
microprocessor from destruction.
OUTPUT ENABLE AND UVLO
The input supply (VCC) to the controller must be higher than
the UVLO threshold, and the EN pin must be higher than its
logic threshold for the ADP3168 to begin switching. If UVLO is
less than the threshold or the EN pin is a logic low, the
ADP3168 is disabled. This holds the PWM outputs at ground,
shorts the DELAY capacitor to ground, and holds the ILIMIT
pin at ground.
In the application circuit, the ILIMIT pin should be connected
to the OD pins of the ADP3418 drivers. Because ILIMIT is
grounded, this disables the drivers so that both DRVH and
DRVL are grounded. This feature is important to prevent
discharging of the output capacitors when the controller is shut
off. If the driver outputs were not disabled, a negative voltage
could be generated on the output due to the high current
discharge of the output capacitors through the inductors.