ADP1763

Data Sheet

Rev. 0 | Page 14 of 18

Therefore, the capacitor chosen in this example meets the

minimum capacitance requirement of the LDO over temperature

and tolerance at the chosen output voltage.

To guarantee the performance of the ADP1763, it is imperative

that the effects of dc bias, temperature, and tolerances on the

behavior of the capacitors be evaluated for each application.

UNDERVOLTAGE LOCKOUT

The ADP1763 has an internal undervoltage lockout circuit that

disables all inputs and the output when the input voltage is less

than approximately 1.06 V. The UVLO ensures that the ADP1763

inputs and the output behave in a predictable manner during

power-up.

CURRENT-LIMIT AND THERMAL OVERLOAD

PROTECTION

The ADP1763 is protected against damage due to excessive power

dissipation by current-limit and thermal overload protection

circuits. The ADP1763 is designed to reach the current limit

when the output load reaches 4 A (typical). When the output

load exceeds 4 A, the output voltage is reduced to maintain a

constant current limit.

Thermal overload protection is included, which limits the

junction temperature to a maximum of 150°C (typical). Under

extreme conditions (that is, high ambient temperature and power

dissipation) when the junction temperature begins to rise above

150°C, the output is turned off, reducing the output current to

zero. When the junction temperature drops below 135°C (typical),

the output is turned on again, and the output current is restored

to its nominal value.

Consider the case where a hard short from VOUT to ground

occurs. At first, the ADP1763 reaches the current limit so that

only 4 A is conducted into the short circuit. If self heating of the

junction becomes great enough to cause its temperature to rise

above 150°C, thermal shutdown activates, turning off the output

and reducing the output current to zero. As the junction

temperature cools and drops below 135°C, the output turns on

and conducts 4 A into the short circuit, again causing the

junction temperature to rise above 150°C. This thermal oscillation

between 135°C and 150°C causes a current oscillation between

4 A and 0 A that continues as long as the short circuit remains

at the output.

Current-limit and thermal overload protections are intended to

protect the device against accidental overload conditions. For

reliable operation, limit device power dissipation externally so that

junction temperatures do not exceed 125°C.

PARALLELING ADP1763 FOR HIGH CURRENT

APPLICATIONS

In applications where high output current is required while

maintaining low noise and high PSRR performance, connect two

ADP1763 devices in parallel to handle loads up to 5 A.

When paralleling the ADP1763, the two outputs must be of the

same voltage setting to maintain stable current sharing between

the two LDO regulators. To improve current sharing accuracy, add

as shown in Figure 34. Note that large ballast resistors improve

current sharing accuracy but degrade the load regulation perform-

ance and increase the losses along the power line; therefore, it is

recommended to keep the ballast resistors at a minimum. In

addition, tie the VADJ, SS, and REFCAP pins of the LDO regu-

lators together to minimize error between the two outputs.

VIN

EN

ENABLE

SS

VREG

VOUT

SENSE

10µF

PG

VADJ

GND

REFCAP

10µF

ADP1763

VIN

EN

SS

VREG

VOUT

SENSE

10µF

PG

VADJ

GND

REFCAP

10µF

ADP1763

1µF

1µF

4.02kΩ

100kΩ

1nF

1µF

1µF

Figure 34. Two ADP1763 Devices Connected in Parallel to Achieve Higher Current Output