Datasheet

Data Sheet ADP2323
Rev. A | Page 17 of 32
The ADP2323 uses hiccup mode for overcurrent protection.
When the peak inductor current reaches the current-limit
threshold, the high-side MOSFET turns off and the low-side
driver turns on until the next cycle while the overcurrent
counter increments.
If the overcurrent counter reaches 10, or the FBx pin voltage falls
to 0.51 V after the soft start, the device enters hiccup mode. During
this mode, the high-side MOSFET and low-side driver are both
turned off. The device remains in this mode for seven soft start
times and then attempts to restart from soft start. If the current-
limit fault is cleared, the device resumes normal operation;
otherwise, it reenters hiccup mode.
In some cases, the input voltage (PVIN) ramp rate is too slow or
the output capacitor is too large to support the setting regulation
voltage during the soft start causing the device to enter the
hiccup mode. To avoid such cases, use a resistor divider at the
ENx pin to program the input voltage UVLO or use a longer
soft start time.
VOLTAGE TRACKING
The ADP2323 has a tracking input, TRKx, that allows the output
voltage to track an external (master) voltage. It allows power
sequencing applicable to FPGAs, DSPs, and ASICs, which may
require a power sequence between the core and the I/O voltages.
The internal error amplifier includes three positive inputs: the
internal reference voltage, the soft start voltage, and the tracking
input voltage. The error amplifier regulates the feedback voltage
to the lowest of the three voltages. To track a master voltage, tie the
TRKx pin to a resistor divider from the master voltage as shown
in Figure 43.
FBx
TRKx SWx
ADP2323
V
MASTER
R
TRK_TOP
R
TRK_BOT
V
SLAVE
R
TOP
R
BOT
09357-045
Figure 43. Voltage Tracking
A common application is coincident tracking, which is shown in
Figure 44. Coincident tracking limits the slave output voltage to
be the same as the master voltage until it reaches regulation. For
coincident tracking, set R
TRK_TOP
= R
TOP
and R
TRK_BOT
= R
BOT
.
TIME
VOLTAGE
V
MASTER
V
SLAVE
09357-046
Figure 44. Coincident Tracking
Ratiometric tracking is shown in Figure 45. The slave output is
limited to a fraction of the master voltage. In this application, the
slave and master voltages reach the final value at the same time.
TIME
VOLTAGE
V
MASTER
V
SLAVE
09357-047
Figure 45. Ratiometric Tracking
The ratio of the slave output voltage to the master voltage is a
function of the two dividers, as follows:
BOTTRK
TOPTRK
BOT
TOP
MASTER
SLAVE
R
R
R
R
V
V
_
_
1
1
+
+
=
The final TRKx pin voltage must be higher than 0.54 V. If the
TRK function is not used, connect the TRKx pin to INTVCC.
PARALLEL OPERATION
ADP2323 supports a two phase parallel operation to provide a
single output of 6 A. To configure the ADP2323 as a two phase
single output
1. Connect the FB2 pin to INTVCC, thereby disabling the
Channel 2 error amplifier.
2. Connect COMP1 to COMP2 and connect EN1 to EN2.
3. Use SS1 to set the soft start time and keep SS2 open.
During parallel operation, the voltages of PVIN1 and PVIN2
should be the same.
POWER GOOD
The power good (PGOODx) pin is an active high, open drain
output that indicates if the regulator output voltage is within
regulation. High indicates that the voltage at an FBx pin (and,
hence, the output voltage) is above 90% of the reference voltage.
Low indicates that the voltage at an FBx pin (and, hence, the
output voltage) is below 85% of the reference voltage. There is a
16-cycle deglitch time between FBx and PGOODx.
OVERVOLTAGE PROTECTION
The ADP2323 provides an overvoltage protection (OVP)
feature to protect the system against the output shorting to a
higher voltage supply or when a strong load transient occurs. If
the feedback voltage increases to 0.7 V, the internal high-side
MOSFET and low-side driver turn off until the voltage at the
FBx pin reduces to 0.63 V, at which time the ADP2323 resumes
normal operation.