ADP2325ACPZ-R7 datasheet(18/32 Pages) AD

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ADP2325

Data Sheet

Rev. 0 | 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 RTRK_TOP = RTOP and RTRK_BOT = RBOT.

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:

BOT

TRK

TOP

TRK

BOT

TOP

MASTER

SLAVE

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

VMASTER

RTRK_TOP

RTRK_BOT

VSLAVE

RTOP

RBOT

TIME

VMASTER

VSLAVE

TIME

VMASTER

VSLAVE

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