ADP2441ACPZ-R2 datasheet(17/32 Pages) AD

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Data Sheet

ADP2441

Rev. A | Page 17 of 32

Coincident Tracking

The most common mode of tracking is coincident tracking. In this

method, the slope of the slave voltage matches that of the master

voltage, as shown in Figure 51. As the master voltage rises, the

slave voltage rises identically. Eventually, the slave voltage reaches

its regulation voltage, at which point the internal reference takes

over the regulation while the SS/TRK input continues to increase,

thus preventing itself from influencing the output voltage.

TIME

MASTER VOLTAGE

SLAVE VOLTAGE

Figure 51. Coincident Tracking

For coincident tracking, select resistor values such that RTRK_TOP

= RTOP and RTRK_BOT = RBOTTOM in Equation 1.

Ratiometric Tracking

In the ratiometric tracking scheme, the master and the slave

voltages rise with different slopes.

TIME

MASTER VOLTAGE

SLAVE VOLTAGE

Figure 52. Ratiometric Tracking

For ratiometric tracking in which the master voltage rises faster

than the slave voltage (as shown in Figure 52), select RTRK_TOP ≥

RTOP and RTRK_BOT = RBOTTOM in Equation 1.

UNDERVOLTAGE LOCKOUT (UVLO)

The UVLO function prevents the IC from turning on while the

input voltage is below the specified operating range to avoid an

undesired operating mode. If the input voltage drops below the

specified range, the UVLO function shuts off the device. The

rising input voltage threshold for the UVLO function is 4.2 V

with 200 mV hysteresis. The 200 mV of hysteresis prevents the

regulator from turning on and off repeatedly with slow voltage

ramp on the VIN pin.

PRECISION ENABLE/SHUTDOWN

The ADP2441 features a precision enable pin (EN) that can be used

to enable or shut down the device. The ±5% accuracy lends

itself to using a resistor divider from the VIN pin (or another

external supply) to program a desired UVLO threshold that is

higher than the fixed internal UVLO of 4.2 V. The hysteresis is

100 mV.

If a resistor divider is not used, a logic signal can be applied. A

logic high enables the part, and a logic low forces the part into

shutdown mode.

VIN

FREQ AGND COMP

ADP2441

VOUT

VIN

BST

Figure 53. Precision Enable Used as a Programmable UVLO

CURRENT-LIMIT AND SHORT-CIRCUIT

PROTECTION

The ADP2441 has a current-limit comparator that compares

the current sensed across the low-side power MOSFET to the

internally set reference current. If the sensed current exceeds

the reference current, the high-side power MOSFET is not

turned on in the next cycle and the low-side power MOSFET

stays on until the inductor current ramps down below the

current-limit level.

If the output is overloaded and the peak inductor current exceeds

the preset current limit for more than eight consecutive clock

cycles, the hiccup mode current-limit condition occurs. The

output goes to sleep for 6 ms, during which time the output is

discharged, the average power dissipation is reduced, and the

part wakes up with a soft start period. If the current-limit condition

is triggered again, the output goes to sleep and wakes up after 6 ms.

Figure 32 shows the current-limit hiccup mode when the output

is shorted to PGND.

THERMAL SHUTDOWN

If the ADP2441 junction temperature rises above 150°C, the

thermal shutdown circuit turns off the switching regulator. Extreme

junction temperatures can be the result of high current operation,

poor circuit board design, or high ambient temperature. A 25°C

hysteresis is included so that when a thermal shutdown occurs,

the ADP2441 does not return to normal operation until the

junction temperature drops below 125°C. Soft start is active

upon each restart cycle.

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