Datasheet

ADP2325 Data Sheet
Rev. A | Page 18 of 32
If the overcurrent counter reaches 10, or if the FBx pin voltage
falls to 0.2 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 cycles 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.
The ADP2325 provides a negative current limit. When the low-side
FET voltage exceeds the negative current-limit threshold voltage
(50 mV typical), the low-side FET turns off immediately for the
remainder of this cycle. Both the high-side and low-side FETs
turn off until the next cycle.
In some cases, the input voltage (PVIN) ramp rate is too slow
or the output capacitor is too large to support the set regulation
voltage during the soft start, causing the device to enter the
hiccup mode. To prevent such cases, use a resistor divider at the
ENx pin to program the UVLO of the input voltage or use a
longer soft start time.
VOLTAGE TRACKING
The ADP2325 has a tracking input, TRKx, that allows the output
voltage to track an external (master) voltage. Voltage tracking
allows power sequencing applicable for 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,
connect the TRKx pin to a resistor divider from the master
voltage, as shown in Figure 47.
Figure 47. Voltage Tracking
Coincident Tracking
A common application is coincident tracking, which is shown in
Figure 48. Coincident tracking limits the slave output voltage to
be the same as the master voltage until it reaches regulation. To
enable coincident tracking, set R
TRK_TOP
= R
TOP
and R
TRK_BOT
= R
BOT
.
Figure 48. Coincident Tracking
Ratiometric Tracking
In ratiometric tracking, the slave output voltage is limited to a frac-
tion of the master voltage. In this application, the slave and master
voltages reach their final values at the same time (see Figure 49).
Figure 49. 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
tracking function is not used, connect the TRKx pin to INTVCC.
PARALLEL OPERATION
The ADP2325 supports a 2-phase parallel operation to provide
a single output of 10 A. To configure the ADP2325 as a 2-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.
FBx
TRKx SWx
ADP2325
V
MASTER
R
TRK_TOP
R
TRK_BOT
V
SLAVE
R
TOP
R
BOT
10036-043
TIME
VOLTAGE
V
MASTER
V
SLAVE
10036-044
TIME
VOLTAGE
V
MASTER
V
SLAVE
10036-045