ADP3209 ON Semiconductor, ADP3209 Datasheet - Page 18

• Manufacturer Part Number: ADP3209
• Description: 5-bit, Programmable, Single-phase, Synchronous Buck Controller
• Manufacturer: ON Semiconductor

ADP3209
switch voltage approaches 0 V, as seen just before t
switch voltage is approximately −6 mV, the low-side FET is
turned off.
Figure 29 shows a small, dampened ringing at t
by the LC created from capacitance on the switch node,
including the C
ringing is normal.
The ADP3209 automatically goes into DCM with a light load.
Figure 30 shows the typical DCM waveform of the ADP3209
with a 1 A load current. As the load increases, the ADP3209
enters into CCM. In DCM, frequency decreases with load
current, and switching frequency is a function of the inductor,
load current, input voltage, and output voltage.
VOLTAGE
INPUT
Figure 26. Buck Topology Inductor Current During t
Figure 27. Buck Topology Inductor Current During t
Figure 28. Buck Topology Inductor Current During t
DS
of the FETs and the output inductor. This
DRVH
DRVL
Figure 25. Buck Topology
OFF
OFF
OFF
OFF
ON
ON
Q1
Q2
SWITCH
NODE
L
L
L
L
C
C
C
C
2
. This is caused
VOLTAGE
OUTPUT
LOAD
LOAD
2
LOAD
0
1
2
. When the
and t
and t
and t
Rev. 2 | Page 18 of 32 | www.onsemi.com
LOAD
1
2
3
OUTPUT CROWBAR
To protect the load and output components of the supply, the
DRVL output is driven high (turning the low-side MOSFETs on)
and DRVH is driven low (turning the high-side MOSFETs off)
when the output voltage exceeds the GMCH OVP threshold.
Turning on the low-side MOSFETs forces the output capacitor
to discharge and the current to reverse due to current build up
in the inductors. If the output overvoltage is due to a drain-
source short of the high-side MOSFET, turning on the low-side
MOSFET results in a crowbar across the input voltage rail. The
crowbar action blows the fuse of the input rail, breaking the
circuit and thus protecting the GMCH chipset from destruction.
When the OVP feature is triggered, the ADP3209 is latched off.
The latch-off function can be reset by removing and reapplying
VCC to the ADP3209 or by briefly pulling the EN pin low.
REVERSE VOLTAGE PROTECTION
Very large reverse current in inductors can cause negative
V
components. The ADP3209 provides a reverse voltage
CCGFX
INDUCTOR
CURRENT
VOLTAGE
SWITCH
Figure 30. Single-Phase Waveforms in DCM with 1 A Load Current
NODE
voltage, which is harmful to the chipset and other output
3
4
2
1
Figure 29. Inductor Current and Switch Node in DCM
t
0
t
SWITCH NODE 5V/DIV
LOW-SIDE GATE DRIVE 5V/DIV
1
OUTPUT VOLTAGE
INDUCTOR CURRENT
20mV/DIV
5A/DIV
2μs/DIV
t
2
t
3
t
4