Analog Devices ADP50460008 Owner's Manual page 29

ADI Confidential
Channel 4 Buck Regulator
The Channel 4 buck regulator is a highly efficient step-down
dc-to-dc converter that utilizes a high speed, fixed-frequency
current mode architecture. No external compensation is needed.
The regulator maintains a constant output voltage regardless of
load by adjusting the peak inductor current threshold and the
duty cycle of the power switches. At the start of each oscillator
cycle, the PFET switch is turned on, sending a positive voltage
across the inductor. Current in the inductor increases until the
current sense signal crosses the peak inductor current threshold,
which turns off the PFET switch and turns on the NFET
synchronous rectifier. This sends a negative voltage across the
inductor, causing the inductor current to decrease. The
synchronous rectifier stays on for the rest of the cycle.
Channel 4 has protection circuitry to limit the amount of
positive current flowing through the PFET switch and the
synchronous rectifier. The positive current limit on the power
switch limits the amount of current that can flow from the input
to the output.
The output voltage of Channel 4 is programmable through the
I 2 C interface (see Table 37 and Table 39). The Channel 4 block
has an adjustable mode, as well, that can be programmed
externally through a resistor divider to a value between 0.5 V and
V × 0.95. Note that an output voltage setting that is too low
IN
(for example, 0.5 V) may go out of regulation at high V
conditions due to the minimum time limitation of Channel 4.
DISCHARGE
SWITCH
FB4
3G
IN
CURRENT SENSE AMP
MAX DUTY
PWM COMP
ERROR AMP
2.5MHz
REF
Figure 51. Channel 4 Buck Regulator Block Diagram
Rev. Sp0 | Page 29 of 60
Channel 4 includes an internal soft start function that ramps
the output voltage in a controlled manner upon startup, thereby
limiting the inrush current. This prevents possible input voltage
drops when a battery is connected to the input of the converter.
The soft start time can be programmed through the I
and set to 1.3 ms or 4 ms.
Channel 4 can start up from any voltage between 0 V and the
final target output voltage without discharging output capacitor
charge at the beginning of the soft start.
When Channel 4 is disabled, there is an option to automatically
discharge the converter output capacitor though a discharge switch.
This discharge function can be enabled through the I
The overvoltage or the undervoltage status of each channel can
be read back through the I 2 C interface.
The regulator discharge switch for Channel 4 is controlled by
Bit 4 in Register DSCG at Address 1 (see Table 14 and Table 15).
The regulator soft start ramp for Channel 4 is controlled by Bit 4
in Register SFTTIM at Address 2 (see Table 16, Table 17, and
Table 18).
The output voltage level of Channel 4 is controlled by Bits[1:0] in
Register VID34 at Address 9 (see Table 37 and Table 39).
The undervoltage and the overvoltage protection status for
Channel 4 is confirmed by Bit 3 in Register UVPST at Address 12
(see Table 45 and Table 46).
ANTI-SHOOT-
THROUGH
ADP50460008
2
C interface
2
C interface.
PVIN4
5H
+
Li+
–
PGND4
SW4
4H
PGND4
3H