feature

Maximum Output Current: 500mA ; Input Voltage Range: 2.5 V to 5.5 V; Low Shutdown Current: <1µA; Low Dropout: 250mV at 500mA Load; 50mV at 100mA Load; Initial Accuracy: ±1%; Line, Load, and Temperature Accuracy: ±3%; 16 Fixed Output Voltage Options with Soft Start: 0.75 V to 3.3 V ( ADP1715 ); Adjustable Output Voltage Options: 0.8 V to 5.0 V (ADP1715 Adjustable ); 16 fixed output voltage options with tracking: 0.75V to 3.3V (ADP1716); small 2.2µF ceramic output capacitor is stable with good load/line transient response; current limit and thermal overload protection logic controls enable 8-lead thermal Enhanced MSOP encapsulation.

application

Buying notebook computers; memory components; telecommunications equipment; network equipment; DSP/FPGA/μP power supply; instrumentation equipment/data acquisition system.

General Instructions

The ADP1715/ADP1716 are low-power CMOS linear regulators that operate from 2.5V to 5.5V and output currents up to 500mA. Using an advanced proprietary architecture, they provide high power supply rejection and achieve good line and load transient response with only a small 2.2µF ceramic output capacitor.

There are three versions of this part, one with fixed output voltage option and variable soft start (ADP1715), one with adjustable output voltage and fixed soft start (ADP1715 adjustable), and one with voltage tracking in fixed output voltage option (ADP1716) . Fixed output voltage option is internally set to one of 16 values between 0.75 V and 3.3 V; adjustable output voltage can be set to any between 0.8 V and 5.0 V via an external voltage divider (connected from OUT to ADJ) value. Variable soft-start uses an external capacitor at SS to control the output voltage ramp. Tracking limits the output voltage to the at or low voltage at the TRK pin.

Housed in an 8-lead thermally enhanced MSOP package, the ADP1715/ADP1716 is not only a very compact solution, but also provides excellent thermal performance for applications requiring up to 500 mA of output current in a small footprint and small form factor.

Absolute Maximum Ratings

Stresses above the Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device under the conditions described in the operating section of this specification or any other conditions above is not implied. Long-term exposure to absolute maximum rating conditions may affect device reliability.

Thermal resistance

θJA is specified for worst-case, devices soldered in circuit boards intended for surface mount packages.

Typical performance characteristics

V=3.8V, I=10mA, C=2.2µF, C=2.2µF, T=25°C unless otherwise noted.

theory of operation

The ADP1715/ADP1716 are low power CMOS linear regulators with an advanced proprietary architecture that requires only a 2.2µF ceramic output capacitor to provide high power supply rejection ratio (PSRR) and excellent line and load transient response . Both devices operate from a 2.5V to 5.5V input rail and provide up to 500mA of output current. Supply current in shutdown mode is typically 100 mA.

Internally, the ADP1715/ADP1716 consist of a reference, an error amplifier, a feedback divider, and a PMOS pass transistor. The output current is passed through a PMOS pass device controlled by an error amplifier. The error amplifier compares the reference voltage to the feedback voltage from the output and amplifies the difference. If the feedback voltage is lower than the reference voltage, the gate of the PMOS device is pulled low, allowing more current to flow through and increasing the output voltage. If the feedback voltage is higher than the reference voltage, the gate of the PMOS device is pulled higher, less current is allowed to pass, and the output voltage is lowered.

The ADP1715 is available in two versions, one with a fixed output voltage option and one with an adjustable output voltage. The fixed output voltage option is internally set to one of sixteen values between 0.75 V and 3.3 V using an internal feedback network. Adjustable output voltage can be set to

0.8 V and 5.0 V are connected to ADJ by external voltage dividers. The fixed output version of the ADP1715 allows the connection of an external soft-start capacitor that controls the output voltage ramp during startup. The ADP1716 has a tracking pin and offers a fixed output voltage option. All devices are controlled by an enable pin (EN).

Soft-Start Function (ADP1715)

For applications requiring controlled start-up, the ADP1715 provides a programmable soft-start function. Programmable soft-start helps reduce inrush current at startup and provides voltage sequencing. To achieve soft start, connect a small ceramic capacitor from SS to GND. At startup, a 1.2µA current source charges this capacitor. The startup output voltage of the ADP1715 is limited by the voltage at SS, providing a smooth ramp up to the rated output voltage. The soft-start time is given by:

Where: TSS is the soft-start period; VREF is the 0.8 V reference voltage; CSS is the soft-start capacitor from SS to GND; ISS is the current from SS (1.2 μA).

When the ADP1715 is disabled (using EN), the soft-start capacitor discharges to GND through an internal 100Ω resistor.

The adjustable version of the ADP1715 and the ADP1716 do not have pins for soft-start, so the function switches to the internal soft-start capacitor. This sets the soft-start ramp period to about 24µs. For a worst-case 5 V output voltage, using the recommended 2.2 μF output capacitor, the resulting input surge current is approximately 460 mA, which is less than the maximum 500 mA load current.

Adjustable Output Voltage (ADP1715 Adjustable)

The adjustable version of the ADP1715 can set its output voltage from 0.8 V to 5.0 V. Set the output voltage by connecting a resistor divider from OUT to ADJ. The output voltage is calculated using the equation:

Where: R1 is the resistance from OUT to ADJ; R2 is the resistance from ADJ to GND; the maximum bias current into the ADJ is 100 mA, so for less than 0.5% error due to bias current, use less than 60 kΩ value as R2.

Orbit Mode (ADP1716)

The ADP1716 includes track mode functionality. As shown in Figure 29, if the voltage applied to the TRK pin is less than the nominal output voltage, then OUT is equal to the voltage on TRK. Otherwise, it will exceed its nominal output value.

For example, consider the ADP1716 with a nominal output voltage of 3V. If the voltage applied to its TRK pin is greater than 3V, OUT will maintain its nominal output voltage of 3V. If the voltage applied to TRK drops below 3V, OUT will track that voltage. OUT can track the TRK pin voltage from nominal all the way to 0 V. There is a voltage divider from TRK to the error amplifier input with a voltage divider ratio equal to the voltage divider from OUT to the error amplifier. This sets the output voltage equal to the tracking voltage. Depending on the desired output voltage, both divider ratios are set by post-package trimming.

enable function

The ADP1715/ADP1716 use the EN pin to enable and disable the OUT pin under normal operating conditions. As shown in Figure 30, when the rising voltage on EN exceeds the activation threshold, OUT turns on. When the falling voltage on EN exceeds the inactivity threshold, OUT turns off.

As you can see, hysteresis is built into the EN pin. This prevents on/off oscillations due to noise when the EN pin passes the threshold point.

The EN-pin activation/inactivation threshold is derived from the input voltage. Therefore, these thresholds vary with the input voltage. Figure 31 shows typical EN activation/inactivation thresholds when the input voltage varies from 2.5 V to 5.5 V.

application information

Capacitor selection

output capacitor

The ADP1715/ADP1716 are designed for small, space-saving ceramic capacitors, but they will work with the most commonly used capacitors as long as the effective series resistance (ESR) value is noted. The ESR of the output capacitor affects the stability of the LDO control loop. A minimum 2.2μF capacitor is recommended with an ESR of 500 mΩ or less to ensure the stability of the ADP1715/ADP1716. The transient response to load current changes is also affected by the output capacitance. Using a larger value of the output capacitor improves the transient response of the ADP1715/ADP1716 to changes in load current. Figure 32 and Figure 33 show the transient responses for output capacitor values of 2.2µF and 22µF.

Input Bypass Capacitor

Connecting a 2.2µF capacitor from IN-pin to GND reduces the sensitivity of the circuit to printed circuit board (PCB) layout, especially when long input traces or high source impedances are encountered. If an output capacitance greater than 2.2µF is required, the input capacitance should be increased to match.

Input and output capacitance characteristics

Any high quality ceramic capacitors can be used with the ADP1715/ADP1716 as long as they meet the minimum capacitance and maximum ESR requirements. Ceramic capacitors are made from a variety of different dielectrics, each of which behaves differently with temperature and applied voltage. Capacitors must have sufficient dielectric to ensure minimum capacitance over the necessary temperature range and DC bias conditions. X5R or X7R dielectrics rated at 6.3 V or 10 V are recommended. Y5V and Z5U dielectrics are not recommended due to their poor temperature and DC bias characteristics.

Current limiting and thermal overload protection

The ADP1715/ADP1716 protect against damage due to excessive power dissipation in the current and thermal overload protection circuits. The ADP1715/ADP1716 are designed to be current limited when the output load reaches 750 mA (typ). When the output load exceeds 750ma, the output voltage is reduced to maintain a constant current limit.

Includes thermal overload protection to limit connection temperature to a maximum of 150°C (typical). Under extreme conditions (i.e. high ambient temperature and high 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, the output is turned on again and the output current returns to its nominal value.

Consider a hard short from outside to ground. First the ADP1715/ADP1716 will limit the current so only 750mA goes into the short circuit. If the self-heating of the junction is sufficient to raise its temperature above 150°C, thermal shutdown will activate, shutting down the output and reducing the output current to zero. When the junction temperature cools and falls below 135°C, the output turns on and conducts 750 mA into the short, again causing the junction temperature to rise above 150°C. Thermal oscillations between 135°C and 150°C result in current oscillations between 750mA and 0mA, which will continue as long as the short remains at the output.

Current and thermal limit protection is designed to protect the unit from accidental overload conditions. For reliable operation, the power consumption of the device should be limited externally so that the connection temperature does not exceed 125°C.

Thermal factor

To ensure reliable operation, the junction temperature of the ADP1715/ADP1716 should not exceed 125°C. To ensure that the junction temperature is below this maximum, the user should understand the parameters that cause the junction temperature to vary. These parameters include ambient temperature, power dissipation in the power device, and thermal resistance (θJA) between the junction and ambient air. The θJA number depends on the package assembly compound used and the amount of copper the package's ground pins are soldered to the PCB. Table 5 shows typical θJA values for 8-lead thermally enhanced MSOP packages with different PCB copper dimensions.

The junction temperature of the ADP1715/ADP1716 can be calculated from:

Where: TA is the ambient temperature; PD is the power dissipation in the die, given by:

Where: ILOAD is the load current; IGND is the ground current; VIN and VOUT are the input and output voltages, respectively.

The power dissipation due to ground current is small and negligible. Therefore, the junction temperature equation simplifies to:

As shown in Equation 5, for a given ambient temperature, input-output voltage differential, and continuous load current, there is a minimum copper size requirement for the PCB to ensure that the junction temperature does not exceed 125°C. The graphs below show the calculated junction temperature, load current, VIN vs. output voltage difference at different ambient temperatures, and the area of the printed circuit board copper.

PCB Layout Considerations

The 8-lead MSOP package has four ground pins fused together inside, enhancing its thermal characteristics. Thermal dissipation of the package can be increased by connecting as much copper as possible to the four ground pins of the ADP1715/ADP1716. As can be seen from Table 5, a point of diminishing returns is eventually reached, beyond which the increase in copper size produces no additional thermal benefit.

Figure 46 shows a typical layout for the ADP1715/ADP1716. The four ground pins are connected to a large copper pad. If a second layer is available, multiple vias can be used to connect them, increasing the overall copper area. Input capacitors should be placed as close as possible to the input and ground pins.

The output capacitors should be placed as close as possible to the output and ground pins. 0603 or 0402 sized capacitors and resistors should be used to achieve the smallest possible footprint solution on a board with limited area.

Dimensions