feature

6 MHz fixed frequency operation 35 µA typical quiescent current  Best-in-class load transient response Best-in-class efficiency 600 mA or 750 mA output current capability 2.3 V to 5.5 V Input voltage range 1.0 to 1.90 V Fixed output voltage Low ripple Light Load PFM Mode Forced PWM and External Clock Synchronization Internal Soft-Start Input Under-Voltage Lockout (UVLO) Thermal Shutdown and Overload Protection 6-pump WLCSP, 0.4 mm pitch 6-pin 2 x 2 mm UMLP

application

Mobile phone, smartphone tablet, netbook 8482 ; ultra-mobile PC3G, LTE, WiMAX™, WiBro™ and WiFi data card Game equipment, digital camera DC/DC micro-module

illustrate

The FAN5361 is a 600mA or 750mA, step down, SW itch supply from 2.3V to 5.5V input voltage. Using a proprietary architecture with synchronous rectification, the FAN5361 is able to deliver 92% peak efficiency while maintaining over 80% efficiency at load currents as low as 1mA. The regulator operates at 6 MHz, reduces the value of external components with an output inductance of 470nh and an output capacitor of 4.7µF. The PWM modulator can be synchronized to an external frequency source. At moderate and light loads, Pulse Frequency Modulation is used in power save mode with a typical quiescent current of 35µA, and even at this low voltage quiescent current, the parts show excellent transients for heavy load switching response during the period. At higher loads the system automatically switches to fixed frequency control, operating at 6 MHz. In shutdown mode, the power supply drops below 1 microamp, reducing power consumption. For applications requiring minimal ripple or fixed frequency, PFM mode can be disabled using the mode pin. The FAN5361 is available in a 6-bump, 0.4mm pitch, waffle-scale chip-scale package (WLCSP) and a 6-lead 2 x 2mm ultra-thin MLP package (UMLP).

Absolute Maximum Ratio Pressure exceeding the Absolute Maximum Ratio may damage the equipment. The device may not function or operate on it. The recommended operating conditions and stressing the parts to these levels is not recommended. Added, extended Exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratio pressure ratio is only

Typical Performance Characteristics (continued) Unless otherwise noted, VIN=VEN=3.6 V, VIN=0 V (auto mode), VIN=1.82 V, TEM=25°C, 5 μs/ Index level switch eep.

Instructions

FAN5361 is a 600 mA or 750 mA, step-down, southwest itching, voltage regulator with a fixed output from the input terminal. 2.3 V to 5.5 V power supply, using a dedicated structure with synchronous rectification, FAN5361 can provide 92% Peak efficiency at load currents as low as 1 mA. The regulator operates at 6 MHz at full load, which reduces the external inductor to 470 nH and the inductor to a 4.7µF output capacitor. The control scheme FAN5361 uses a proprietary, non-linear, fixed frequency PWM modulator that provides fast load transient response while maintaining a constant switch frequency operating condition range. The regulator performance is independent of the output capacitor ESR, allowing the use of ceramic output capacitors. Although this procedure typically results in a swizzling frequency that varies with input voltage and load current, the internal frequency loop maintains switching frequency constant over a wide range of input voltage and load current. For very light loads, the FAN5361 operates in discontinuous current mode (DCM) single-pulse power factor modulation mode with less output ripple compared to other power factor modulation architectures. Transitions between PWM and power factor modulation are seamless, with less than 18 mV of fault during VOUT transitions between DCM and CCM modes.

Combined with exceptional transient response, the extremely low quiescent current controller (35µA) maintains high efficiency; even at very light loads, while maintaining fast transient response for applications requiring tight output regulation. Enable and Soft Start When EN is low, all circuits in the FAN5361 are disconnected and the IC draws a current of s~50na. When EN is high and the VIN is above its UVLO threshold, the regulator begins a soft-start cycle. The output ramp during this soft-start is a fixed slew rate of 50 mV/(s) from 0 to 1 volt, then 12.5 mV/s until the output reaches its set value. Regardless of the state of the mode pin, PFM mode is enabled to prevent current from discharging from COUT if soft-start is initiated while charging. If a heavy load is applied during startup, the IC may fail to start and/or if excessive COUT is used. This is due to the current limit fault response, which has an overcurrent condition during a soft start. The current required for charging during soft start is the formula commonly referred to as the "displacement current" as follows:

The term here refers to the aforementioned soft-start slew rate. To prevent DOWN from turning off during soft start, the following conditions must be met:

Here IMAX(DC) is the maximum load current of the IC. Guaranteed support (600mA or 750mA). Table 1 shows the combinations of COUT s that allow the IC to start to operate successfully with the minimum supported load. Table 1. Soft-start minimum load value for various COUT values

A logic 1 on this pin forces the IC to remain in PWM mode. A logic 0 allows the IC to be under light load. If the mode pin is toggled, the converter synchronizes its sw frequency to the frequency on the mode pin (f-mode). The mode pin is internally buffered by a Schmitt trigger, which allows the mode pin to rise and fall slowly. The asymmetric duty cycle of the frequency also allows synchronization as long as the time below VIL(max) or above VIH(max) is 100 ns. Current limit, fault shutdown and heavy loads or short circuits on the restart outputs cause the current to increase in the inductor until the maximum current threshold reaches sw on the high side. Reaching this point, the high-side switch itches off, preventing the high-voltage current from causing damage. The regulator continues to limit the current cycle by cycle. After 21µs of current limit, the regulator triggered an overcurrent fault, causing the regulator to shut down the Dow for about 85µs before trying to restart. If the fault is caused by a short circuit, the soft-start circuit attempts to restart and generates an overcurrent fault about 32 μs after that, resulting in a duty cycle of less than 30%, limiting power dissipation. Closed-loop peak current limit ILIM(PK) and open-loop test current limit in electrical systems, ILIM(OL) characteristics table. This is mainly due to the propagation delay of the integrated circuit current limit comparator.

Under-Voltage Lockout (UVLO) When EN is high, the under-voltage lockout keeps the part from operating until the input supply voltage rises high enough for normal operation. This ensures the regulator during startup or shutdown. Thermal Shutdown (TSD) When the mold temperature rises, due to high load conditions and/or high ambient temperature, the output at the mold temperature reaches a complete drop. Its junction temperature thermal shutdown n activation is typically 150°C w with 15°C hysteresis. The minimum off-time effect frequency of the switch, tOFF(min), is 50 ns. This limits the maximum value. The FAN5361 can provide, or the maximum it can, the output voltage at low VINs while maintaining a fixed switching frequency in PWM mode.

When the VIN is low, as long as

When the regulator cannot provide enough duty cycle at 6MHz to maintain regulation. When VOUT is greater than or equal to 1.82 V and at high load currents, the VIN is below 2.9 V (see diagram). The formula for calculating the sw frequency is as follows:

Application Information: The inductor output inductance must be selected for both the desired inductance and the energy handling capability of the application. This inductor value affects the average current limit, PWM to PFM transition point, output voltage ripple, and efficiency. The ripple current (∏I) of the regulator is:

The maximum average load current IMAX(load) and the peak current limit, ILIM(PK), are given by the ripple current, given by:

The transition between PFM and PWM is determined by the zero-crossing of the inductor valley current at point w. The inductor's regulator DC current zero-crossing current, IDCM, is:

The FAN5361 is optimized for L=470 nH operation, but is stable with inductance up to 1.2μH (nominal). Up to 2.2 μH (nominal) can be used; in this case the VIN must be greater than or equal to 2.7 V. Inductors should be rated to maintain at least 80% of their value at ILIM(PK). Efficiency is affected by inductance DCR and inductance value. Decreasing the inductance value for a given physical size generally reduces the DCR; however, as ∏I increases, the RMS current increases, as do core and skin effect losses.

The increased rms current through the integrated circuit mosfet's RDS(ON) is the same as the inductor DCR. Increasing the inductance value produces a lower current rms value, but reduces the transient response. For a given physical inductor size, increasing the inductance typically results in an inductance with low ampere-to-saturation current and high DC ratio. Table 2 shows the regulator performance with inductance above or below the recommended 470 nH. Output Capacitors Table 3 recommends 0402 capacitors. 0603 capacitors can further increase the effective capacitance higher. This improves transient response and output ripple. Increasing COUT has no effect on loop stability and can therefore increase output voltage ripple or improve transient response. The output voltage ripple ∏VOUT is:

Input Capacitor The 2.2µF ceramic input capacitor should be placed as close as possible between the VIN pin and ground to minimize parasitic inductance. If using a long torch the IC's additional "bulk" capacitor (electrolytic or tantalum) should be placed between CIN and the power source resulting in reduced inductance between the power leads and CIN. The effective capacitance value decreases with increasing VIN due to the DC bias effect.

The printed circuit board layout guidelines have only three external components: the inductor and the input and output capacitors. For any buck-sw-itcher IC, including the FAN5361, it is important to place low ESR input capacitors very close to the IC, as shown by n in Figure 41. The input capacitor ensures good input decoupling helps to reduce output terminals and ensures that the control part of the IC does not work unstable due to excessive noise. This reduces sw-itch cycle jitter and ensures good overall performance. It is important to put the common GND of CIN and COUT together as much as possible to connect to the FAN5361 C2 terminal. There is some flexibility for motion sensors further from the IC; in this case, you should consider the couter terminal.