feature

1.2 Maximum Load Current; ±2% Output Accuracy Over Temperature; Wide Input Voltage Range: 3.0 V to 20 V; 700 kHz ( ADP2300 ) or 1.4 MHz (ADP2301); Switching Frequency Options; Efficiency Up to 91%; Current Mode Control architecture; output voltage 0.8 V to 0.85 × VIN; automatic PFM/PWM mode switching; precision enable pin with hysteresis; integrated high-side MOSFET; integrated bootstrap diode; internal compensation and soft-start; minimal external components; undervoltage lockout (UVLO); overcurrent protection (OCP) and thermal shutdown (TSD); available in ultrasmall, 6-lead TSOT package; supported by ADIsimPower 8482 ; design tools.

application

LDO replacement for digital load applications; intermediate power rail conversion; communications and networking; industrial and instrumentation; healthcare; consumer.

General Instructions

The ADP2300/ADP2301 are compact, constant frequency, current mode, step-down DC-DC regulators with integrated power MOSFETs. The input voltage of the ADP2300/ADP2301 devices is 3.0V to 20V , making them suitable for a wide range of applications. An accurate low-voltage internal reference makes these devices ideal for generating regulated output voltages as low as 0.8V with ±2% accuracy and load currents up to 1.2A.

There are two frequency options: the ADP2300 runs at 700kHz and the ADP2301 runs at 1.4MHz. These options allow the user to customize the efficiency and total solution size. Current mode control provides fast settling line and load transient performance. The ADP2300/ADP2301 devices include internal soft-start to prevent inrush current at power-up. Other key safety features include short-circuit protection, thermal shutdown (TSD) and input undervoltage lockout (UVLO). Precision enable pin threshold voltages allow the ADP2300/ADP2301 to be easily sequenced from other input/output supplies. It can also be used as a programmable UVLO input using a resistor divider.

The ADP2300/ADP2301 are available in a 6-wire TSOT package and are rated for a junction temperature range of -40°C to + 125 °C.

Typical performance characteristics

V=3.3 V, T=25°C, V=V unless otherwise noted.

theory of operation

The ADP2300/ADP2301 are non-synchronous step-down DC-DC regulators, each with an integrated high-side power MOSFET. A high switching frequency and ultra-small, 6-wire TSOT package allow for small step-down DC-to-DC regulator solutions.

The ADP2300/ADP2301 can operate from input voltages from 3.0 volts to 20 volts while regulating the output voltage to 0.8 volts. The ADP2300/ADP2301 have two fixed frequency options: 700 kHz (ADP2300) and 1.4 MHz (ADP2301).

Basic operation

The ADP2300/ADP2301 use a fixed frequency, peak current mode PWM control structure at medium and high loads, and pulse skip mode control at light loads to reduce switching losses and improve efficiency. Output regulation is achieved by controlling the duty cycle of the integrated MOSFET when the device operates in fixed frequency PWM mode. When the device operates in pulse-skipping mode under light load, the output voltage is controlled in a hysteretic manner, and the output ripple is larger. In this mode of operation, the regulator periodically stops switching for a few cycles, thereby keeping switching losses to a minimum for improved efficiency.

PWM mode

In PWM mode, the ADP2300/ADP2301 operate at a fixed frequency, set by the internal oscillator. At the beginning of each oscillator cycle, the MOSFET switch turns on, sending a positive voltage across the inductor. The inductor current increases until the current sense signal crosses the inductor current peak threshold that turns off the MOSFET switch; this threshold is set by the error amplifier output. During the off-time of the MOSFET, the inductor current drops through the external diode until the next oscillator clock pulse starts a new cycle. The ADP2300/ADP2301 regulate the output voltage by adjusting the peak inductor current threshold.

power saving mode

For higher efficiency, the ADP2300/ADP2301 smoothly transitions to pulse skip mode when the output load drops below the pulse skip current threshold. When the output voltage drops below the specified value, the ADP2300/ADP2301 enters pulse-width modulation mode for several oscillator cycles until the voltage rises to within the specified value. During the idle time between pulses, the MOSFET switch is turned off and the output capacitor supplies all the output current.

Since the pulse skip mode comparator monitors an internal compensation node that represents inductor current peak information, the average pulse skip load current threshold depends on the input voltage (V), output voltage (V), inductor, and output capacitance. out

Since the output voltage occasionally drops below the specified value and then recovers, the output voltage ripple in power-saving mode is larger than that in PWM operating mode.

Bootstrap circuit

The ADP2300/ADP2301 each have an integrated bootstrap regulator, which requires a 0.1µF ceramic capacitor (X5R or X7R) placed between the BST and SW pins to provide the gate drive voltage for the high-side MOSFET. There must be at least a 1.2v voltage difference between the BST and SW pins to turn on the high-side MOSFET. If an external voltage source is supplied to the BST pin through a diode, this voltage should not exceed 5.5v. The ADP2300/ADP2301 differentially sense and regulate the voltage between the BST and SW pins to generate a typical 5.0V bootstrap voltage for the gate drive circuit. When the MOSFET switch is turned on, the diode integrated on the chip blocks the reverse voltage between the VIN and BST pins.

Precision enabled

The ADP2300/ADP2301 feature a precision enable circuit with a 1.2V reference voltage and 100 mV hysteresis. The part is enabled when the voltage at the EN pin is greater than 1.2v. If the EN voltage is lower than 1.1v, the chip will be disabled. The precision enable threshold voltage allows the ADP2300/ADP2301 to be easily sequenced from other input/output supplies. It can also use a resistive divider as a programmable UVLO input. An internal 1.2µA pull-down current prevents errors if the EN pin is floating.

Integrated soft start

The ADP2300/ADP2301 include internal soft-start circuitry that ramps the output voltage in a controlled manner during startup to limit inrush current. The soft-start time is typically fixed at 1460 microseconds for the ADP2300 and 730 microseconds for the ADP2301.

current limit

The ADP2300/ADP2301 include current limit protection circuitry to limit the amount of positive current flowing through the high-side MOSFET switch. The positive current limit on the power switch limits the amount of current that can be drawn from the input to the output.

Short circuit protection

The ADP2300/ADP2301 include frequency folding to prevent runaway output current in the event of a hard short at the output. When the voltage at the FB pin falls below a certain value, the switching frequency is reduced, which allows the inductor current to drop for a longer time, but increases the ripple current while regulating the peak current. This reduces the average output current and prevents the output current from running out of control. The correlation between switching frequency and FB pin voltage is shown in Table 5.

When a hard short is removed (V≤0.2V), a soft-start cycle is initiated to regulate the output back to normal operating levels, which helps limit inrush current and prevent possible overshoot of the output voltage.

Under Voltage Lockout (UVLO)

The ADP2300/ADP2301 have a fixed, internally programmed undervoltage lockout circuit. If the input voltage falls below 2.4V, the ADP2300/ADP2301 turns off and the MOSFET switch turns off. When the voltage rises above 2.8V again, a soft-start cycle is initiated and the part is enabled.

Thermal shutdown

If the ADP2300/ADP2301 junction temperature rises above 140°C, thermal shutdown circuitry disables the chip. Extreme junction temperatures can be the result of high current operation, poor board design, or excessive ambient temperature. A 15°C hysteresis is included, so when a thermal shutdown occurs, the ADP2300/ADP2301 will not resume operation until the onboard temperature drops below 125°C. After the device has recovered from a thermal shutdown, a soft-start is initiated.

Control loop

The ADP2300/ADP2301 are internally compensated to minimize external component count and cost. In addition, built-in slope compensation helps prevent subharmonic oscillations when the ADP2300/ADP2301 operate at duty cycles greater than or approaching 50%.

application information

ADIsimPower Design Tool

ADP2300/ADP2301 supported by ADIsimPower

Design toolset. ADIsimPower is a set of tools for generating a complete power supply design optimized for specific design goals. These tools enable users to generate complete schematics and bills of materials and calculate performance in minutes. ADIsimPower can optimize designs for cost, area, efficiency, and part count, taking into account the operating conditions and constraints of the IC and all practical external components. For more information on the ADIsimPower design tool, see /ADIsimPower. The toolset is available from this website through which users can request unpopular boards.

Output voltage programming

The output voltage of the ADP2300/ADP2301 is set externally by a resistor divider from the output voltage to the FB pin, as shown in Figure 42. Table 6 lists recommended resistor values for typical output voltage settings. The equation for the output voltage setting is:

where: VOUT is the output voltage. RFB1 is the feedback resistor from VOUT to FB. RFB2 is the feedback resistor from FB to GND.

Voltage Transition Limits

There are lower and higher output voltage limits for a given input voltage due to minimum turn-on time, minimum turn-off time and bootstrap voltage drop.

The lower limit of the output voltage is limited by a finite, controllable minimum turn-on time of up to 135ns in the worst case. Considering the change of switching frequency and input voltage, the lower bound equation of output voltage is:

Where: VIN(max) is the maximum input voltage. Friction stir welding (max) is the worst case maximum switching frequency. tMIN ON is the minimum controllable on time. VD is the diode forward voltage drop.

The upper limit of the output voltage is limited by the minimum controllable off-time, which can be as high as 120ns in the worst case in the ADP2301. Considering the variation of switching frequency and input voltage, the upper limit equation of output voltage is:

Where: VIN(min) is the minimum input voltage. Friction stir welding (max) is the worst case maximum switching frequency. VD is the diode forward voltage drop. tMIN OFF is the minimum controllable off time.

Additionally, the bootstrap circuit limits the minimum input voltage of the desired output due to internal voltage drops. For stable operation at light loads and to ensure proper start-up under pre-bias conditions, the ADP2300/ADP2301 require a worst-case voltage differential between the input voltage and the regulated output voltage (or between the input voltage and pre-bias) greater than 2.1V. If the voltage difference is small, the startup circuit relies on a certain minimum load current to charge the boost capacitor for startup. Figure 43 shows the typical minimum input voltage and load current required for a 3.3V output voltage.

Figure 44 shows the voltage transition limits based on three transition constraints (minimum turn-on time, minimum turn-off time, and bootstrap voltage drop).

Low Input Voltage Considerations

For low input voltages between 3 V and 5 V, the internal bootstrap regulator cannot provide sufficient boot voltage of 5.0 V due to the internal voltage drop. As a result, the increased MOSFET R reduces the available load current. To prevent this, add an external small-signal Schottky diode from the 5.0V external bootstrap bias voltage. Because the absolute maximum rating between the BST and SW pins is 6 V, the bias voltage should be less than 5.5 V. Figure 45 shows the application diagram of the external bootstrap circuit.

programming precision enabled

In general, the EN pin can be easily connected to the VIN pin so that the device starts automatically when the input power is applied. However, the precision enable feature allows the ADP2300/ADP2301 to function as a programmable UVLO by connecting a resistive divider to V, as shown in Figure 46. This configuration prevents starting problems that can occur when V rises slowly with relatively high load currents in soft start.

The precision enable feature also allows the ADP2300/ADP2301 to sequence precisely through the use of a resistive divider and another dc-dc output supply, as shown in Figure 47.

When the pull-down current on the EN pin is 1.2 µA, the startup voltage equations in Figure 46 and Figure 47 are:

Where: VSTARTUP is the startup voltage of the startup chip. REN1 is the resistance from the DC supply to EN. REN2 is the resistor from EN to GND.

sensor

The high switching frequency of the ADP2300/ADP2301 allows the use of small inductors. For optimum performance, use an inductor value between 2μH and 10μH for the ADP2301 and between 2μH and 22μH for the ADP2300.

The formula for calculating the peak-to-peak inductor current ripple is as follows:

where: fSW is the switching frequency. L is the inductance value. VD is the diode forward voltage drop. VIN is the input voltage. VOUT is the output voltage.

Smaller value inductors are generally smaller in size and less expensive, but increase ripple current and output voltage ripple. As a guideline, the inductor peak-to-peak current ripple should typically be set to 30% of the maximum load current for best transient response and efficiency. Therefore, use the following formula to calculate the inductance value:

where ILoad(max) is the maximum load current.

The formula for calculating the peak inductor current is as follows:

The minimum current rating of the inductor must be greater than the peak current of the inductor. For ferrite core inductors with fast saturation characteristics, the inductor saturation current rating should be higher than the switch current limit threshold to prevent the inductor from reaching the saturation point. Be sure to confirm the worst case, short circuit output, over the expected temperature range.

Inductor conduction losses are caused by the current flowing through the inductor, which is related to the internal DC resistance (DCR). Larger size inductors have smaller DCRs and, therefore, reduce the conduction losses of the inductors. However, inductor core losses are also related to the core material and the AC flux swing, which in turn is affected by the inductor ripple current. Since the ADP2300/ADP2301 are high switching frequency regulators, the shielded ferrite core material has the advantages of low core loss and low EMI. Some recommended sensors are shown in Table 7.

capture diode

The capture diode conducts inductor current during the off-time of the internal MOSFET. Therefore, the average current of the diode in normal operation depends on the duty cycle of the regulator and the output load current.

where VD is the diode forward voltage drop.

The only reason to choose a diode with a higher current rating than required for normal operation is in the worst case, where there is a shorted output. In this case, the diode current increases to the typical peak current limit threshold. Be sure to consult the diode data sheet to ensure that the diode will operate within the thermal and electrical limits.

The diode's reverse breakdown voltage rating must be higher than the maximum input voltage with appropriate margin for possible ringing at the SW node. The Schottky diode is recommended for best efficiency due to its reduced forward voltage and fast switching speed. Table 8 lists the recommended Schottky diodes.

input capacitor

The input capacitor must be able to support the maximum input operating voltage and maximum RMS input current. The maximum RMS input current flowing through the input capacitor is I/2. Choose an input capacitor that can withstand the RMS input current of the application's maximum load current, using the following equation:

where D is the duty cycle, equal to

Due to its low ESR and small temperature coefficient, the recommended input capacitors are ceramic X5R or X7R dielectrics. A 10µF capacitor should be sufficient for most applications. To minimize power supply noise, place the input capacitors as close as possible to the VIN pins of the ADP2300/ADP2301.

output capacitor

The choice of output capacitor has an effect on both the regulator's output voltage ripple and loop dynamics. The ADP2300/ADP2301 are designed to work with small ceramic capacitors with low equivalent series resistance (ESR) and equivalent series inductance (ESL), so they can easily meet stringent output voltage ripple specifications.

When the regulator is operating in forced continuous conduction mode, the total output voltage ripple is the sum of the voltage spike caused by the output capacitor ESR plus the voltage ripple caused by charging and discharging the output capacitor.

Capacitors with lower ESR preferably guarantee lower output voltage ripple, as shown in the following equation:

Ceramic capacitors are made from a variety of different dielectrics, each of which behaves differently with temperature and applied voltage. Due to the low ESR and small temperature coefficient of X5R or X7R dielectrics, X5R or X7R dielectrics are recommended for best performance. Y5V and Z5U dielectrics are not recommended due to their poor temperature and DC bias characteristics.

In general, most applications using the ADP2301 (1.4MHz switching frequency) require a minimum output capacitor value of 10μF, while most applications using the ADP2300 (700kHz switching frequency) require a minimum output capacitor value of 20μF. Table 9 lists some recommended output capacitors for V≤5.0V.

Thermal factor

The ADP2300/ADP2301 store the inductor current value only during the on-time of the internal MOSFET. Therefore, a small amount of power is dissipated inside the ADP2300/ADP2301 package, reducing thermal constraints. However, when the application is operating at maximum load, the ambient temperature is high, and the duty cycle is high, heat dissipation within the package can cause the junction temperature of the chip to exceed the maximum junction temperature of 125°C. If the junction temperature exceeds 140°C, the regulator enters thermal shutdown and recovers. when the junction temperature drops below 125°C.

The die attach temperature is the sum of the ambient temperature and the package temperature rise due to power dissipation, as shown in the following equation:

where: TJ is the junction temperature. TA is the ambient temperature. TR is the package temperature rise due to power dissipation.

The increase in package temperature is proportional to the power dissipation in the package. The proportionality constant for this relationship is the thermal resistance from the die junction to ambient temperature as follows:

where: TR is the rise in package temperature. θJA is the ambient temperature from the die joint to the package. PD is the power dissipation in the package.

Design example

This section provides steps to select external components based on the example specifications listed in Table 10. A schematic diagram of this design example is shown in Figure 48.

Switching frequency selection

Select switching frequency - 700 kHz (ADP2300) or 1.4 MHz (ADP2301) - Use the transition limit curve shown in Figure 44 to evaluate transition limits (minimum turn-on time, minimum turn-off time, and bootstrap voltage drop).

For example, in Figure 44, for an output voltage of 3.3v, V=12v±10% is within the transition limits of 700khz and 1.4mhz switching frequency, but choosing 1.4mhz switching frequency provides the smallest size solution. If higher efficiency is required, choose the 700 kHz option; however, the regulator's PCB footprint will be larger due to the larger inductance and output capacitance.

Capture diode selection

Select the capture diode. A Schottky diode is recommended because of its lower forward voltage drop and faster switching speed. During normal operation, at a typical Schottky diode forward voltage, the average capture diode current can be calculated using the following equation:

Where: VOUT = 3.3 V. VIN = 12 V. Dashboard load (max) = 1.2 A. VIN = 0.4 V. Therefore, idode (average) = 0.85 A.

However, in the worst case of an output short, the diode current will increase to 2 A typical, determined by the peak switch current limit (see Table 1). In this case, choosing a B230A, 2.0A/30V surface mount Schottky diode will result in more reliable operation.

Sensor selection

Use the following formula to select the inductor:

Where: VOUT=3.3V, VIN=12V, ILOAD(max)=1.2A, VD=0.4V, fSW=1.4MHz.

This results in L = 5.15 μH. The closest standard value is 4.7 μH; therefore, Δiriple=0.394 A. The calculation method of the inductor peak current is as follows:

Where: ILOAD(max)=1.2A. ΔIRIPPLE=0.394A. Therefore, the calculated peak current of the inductor is 1.397 A.

However, to protect the inductor from reaching saturation under current limiting conditions, the inductor is rated for reliable operation with a saturation current of at least 2.0A. OUTPUT CAPACITOR SELECTION The output capacitor requirements are selected based on the output voltage ripple, according to the following equation:

Where: Δiriple=0.394 A. fSW=1.4 MHz. ΔVRIPPLE=33 mV.

If the ESR of the ceramic capacitor is 3 mΩ, then C = 1.2 μF.

Since the output capacitor is one of two external components that control loop stability, most applications using the ADP2301 (1.4MHz switching frequency) require at least 10µF of capacitance to ensure stability. Based on the recommended external components in Table 11, choose 22µF, with a voltage rating of 6.3v.

Resistor Divider Selection

To select an appropriate resistor divider, first calculate the output feedback resistor divider, then calculate the resistor divider for the programmable V start-up voltage. The output feedback resistor divider is at:

For a 3.3V output voltage, select R=31.6KΩ and R=10.2KΩ as the feedback resistor divider according to the suggested values in Table 11.

The resistor divider for the programmable V start-up voltage is at:

If V=7.8V, choose R=10.2kΩ, then calculate R, which in this case is 56kΩ.

Board Layout Recommendations

Good board layout is critical to getting the best performance from the ADP2300/ADP2301. Improper layout can affect system regulation, stability, and electromagnetic interface (EMI) and electromagnetic compatibility (EMC) performance. An example PCB layout is shown in Figure 50. See the following guidelines for good PCB layout:

(1) Place the input capacitor, inductor, capture diode, output capacitor, and bootstrap capacitor close to the IC and use short traces.

(2) Ensure that the high current loop trace is as short and wide as possible. The high current path is shown in Figure 49.

(3) Maximize the size of the ground metal on the component side to improve heat dissipation.

(4) Use a ground plane with multiple vias to connect to the component side ground to further reduce noise interference on sensitive circuit nodes.

(5) Minimize the length of the FB trace that connects the top of the feedback resistor divider to the output. Also, keep these traces away from high current traces and switching nodes to avoid noise pickup.

Typical Application Circuit