10

Output Voltages

The ISL6414 provides fixed output voltages for use in

Wireless Chipset applications. Internal trimmed resistor

networks set the typical output voltages as shown here:

Shutdown

Driving the SHDN input LOW puts both LDO1 and LDO2 in

shutdown mode. Driving the SHDN3 input LOW puts LDO3

in shutdown mode. Pulling the SHDN and SHDN3 pins LOW

simultaneously, puts the complete chip into shutdown mode,

and supply current drops to 5

µA typical. Both SHDN and

SHDN3 inputs have internal pull-up resistors, so that in

normal operation the outputs are always enabled; external

pull-up resistors are not required. During shutdown mode

using the SHDN pin, the FAULT output will remain HIGH

(refer to Figure 19).

Current Limit

The ISL6414 monitors and controls the pass transistor’s

gate voltage to limit the output current. The current limit for

LDO1 is 550mA, LDO2 is 330mA and LDO3 is 250mA. The

output can be shorted to ground without damaging the part

due to the current limit and thermal protection features.

Thermal Overload Protection

Thermal overload protection limits total power dissipation in

+150°C, the thermal sensor sends a signal to the shutdown

logic, turning off the pass transistor and allowing the IC to

cool. The pass transistor turns on again after the IC’s

junction temperature typically cools by 20°C, resulting in a

pulsed output during continuous thermal overload

conditions. Thermal overload protection protects the

ISL6414 against fault conditions. For continuous operation,

do not exceed the absolute maximum junction temperature

rating of +150°C.

Operating Region and Power Dissipation

The maximum power dissipation of ISL6414 depends on the

thermal resistance of the IC package and circuit board, the

temperature difference between the die junction and ambient

air, and the rate of air flow. The power dissipated in the

device is:

PT = P1 + P2 + P3, where

The maximum power dissipation is:

is the thermal resistance from the junction to the surrounding

environment.

The ISL6414 package features an exposed thermal pad on

its underside. This pad lowers the thermal resistance of the

package by providing a direct heat conduction path from the

die to the PC board. Additionally, the ISL6414’s ground

(GND/GND3) performs the dual function of providing an

electrical connection to system ground and channeling heat

away. Connect the exposed backside pad and GND to the

system ground using a large pad or ground plane, or through

multiple vias to the ground plane layer.

Reverse Input Protection

The ISL6414 has a unique protection scheme that limits the

below GND. The circuitry monitors the polarity of these two

pins, disconnecting the internal circuitry and parasitic diodes

when the applied voltage is reversed. This feature prevents

the device from overheating and damaging an improperly

installed input supply.

Integrator Circuitry

The ISL6414 uses an external 33nF compensation capacitor

for minimizing load and line regulation errors and for

lowering output noise. When the output voltage shifts due to

varying load current or input voltage, the integrator capacitor

voltage is raised or lowered to compensate for the

systematic offset at the error amplifier. Compensation is

limited to ±5% to minimize transient overshoot when the

device goes out of dropout, current limit, or thermal

shutdown.

Fault-Detection Circuitry

The FAULT pin monitors LDO1 output regulation, as well as

fault conditions such as current limit and thermal shutdown.

The FAULT output goes LOW, if the LDO1 output is out of

regulation by ±5.5% (typ.). During shutdown mode using the

SHDN pin, the FAULT output will remain HIGH (refer to

Figure 19).

Applications Information

Capacitor Selection and Regulator Stability

Capacitors are required at the ISL6414’s input and output for

stable operation over the entire load range and the full

temperature range. Use >1µF capacitor at the input of

ISL6414. The input capacitor lowers the source impedance

of the input supply. Larger capacitor values and lower ESR

provides better PSRR and line transient response. The input

capacitor must be located at a distance of not more then 0.5

analog ground. Any good quality ceramic or tantalum can be

used as an input capacitor.

The output capacitor must meet the requirements of minimum

amount of capacitance and ESR for all three LDO’s. The

ISL6414 is specifically designed to work with small ceramic

output capacitors. The output capacitor’s ESR affects stability

and output noise. Use an output capacitor with an ESR of

ISL6414