feature

5.4V to 24V Input Voltage Range

Five Adjustable Outputs: 5V@5A (PWM) 3.3V@5A (PWM) 5V@50mA Always On (Linear) 12V/Adjustable @ 120mA Boost (PWM)

>96% efficiency

Light Load Hysteresis Mode

PWM mode for normal load

Main regulator switch out of phase

300kHz Fixed Frequency Switching

RDS (on) current sense overcurrent

Reduced bill of materials; maximum efficiency

Optional Current Sense Resistor for Precision Overcurrent Discovery

Power good signal for all voltages

Input Under Voltage Lockout (UVLO)

Thermal shutdown

ACPI compliant

24-pin TSSOP

application

laptop

web tablet

battery powered meter

illustrate

The FAN5233 is a high-efficiency, high-accuracy multi-output voltage regulator for battery-powered applications such as notebook computers. It integrates three pulse width modulated switching regulator controllers and a linear regulator for converting 5.4V to 24V voltage used by the notebook battery power input circuit around the microprocessors in these systems. The two main PWM controllers in the FAN5233 use synchronous mode rectification, providing 3.3V and 5V at over 5A each. They are phased out to reduce input ripple current. Input and output voltage utilization Feedback in current mode control allows fast and stable loop response changes over a wide input and output range. Normal operation and hysteretic PWM control under light load control provides greater than 95% input and output variation over a wide range. This third PWM controller produces 12V at 120mA. A proprietary technology is used to sense the RDS(ON) of the output current external mosfet, eliminating the external current sense resistor, saving board space and reducing bill of materials cost. An integrated linear regulator provides backup for light (50mA) loads and is always powered at 5V. Additional FAN5233 features include overvoltage, undervoltage, overcurrent monitors, and thermal shutdown protection. When the signal softens, a good power signal is sent to start complete, and all outputs are set within their ±10% range.

Operating Conditions (continued) Recommended operating conditions unless reference box noted

notes:

1. Minimum input voltage does not include source supply voltage drop due to source resistance. is the operating voltage for static load conditions. For acceptable load transient performance, in the 7.5 to 8.5 volts or higher voltage range, depending on the dynamic load, source impedance and severity of input and output capacitance and inductance values. The user should use expected member values and transient loads.

2. Min/max specifications are guaranteed by design.

Function description

The FAN5233 is a high-efficiency, high-precision DC/DC controller for notebook and other portable applications. It provides all the voltages required by the system electronics: 5V, 3.3V, 12V and 5V - all the time. Both inputs utilize current mode control in the output voltage feedback to allow a wide range of input and output changes. MOSFET RDS based current sensing provides maximum efficiency while also allowing the use of high precision sense resistors. The 3.3V and 5V switching regulator outputs of the 3.3V and 5V architectures of the FAN5233 are generated from the unregulated input voltage using a synchronous buck converter. Both high-side and low-side MOSFETs are N-channel. The 3.3V and 5V switches have current sensing and use MOSFETs to set the output overcurrent threshold RDS, turn on. Each converter has a voltage-sensing feedback pin, the pin that shuts down the converter, and the boost voltage used to drive the high-side MOSFET. If not using a 5V switch, connect SDN5 (pin 17) to SGND (pin 14). If not using a 3.3V switcher, connect SDN3.3 (pin 11) to SGND (pin 14). The design of the FAN5233 will be discussed below with reference to Figures 1 to 4, which show the internal block diagram of the integrated circuit. 3.3V and 5V PWM current sensing Peak current sensing is done on the low side driver because the duty cycle is very low on the high side MOSFET. This samples the current 50ns after power-on and maintains that value for current feedback and overcurrent limiting. 3.3V and 5V PWM Loop Compensation Fan 5233's 3.3V and 5V control loop functions as follows for voltage mode and current feedback stability. Each of them has an independent voltage feedback pin, as shown in Figure 1. They use voltage feedforward to guarantee loop rejection of input voltage changes: that is, the (pulse width modulation) ramp amplitude varies with the input voltage. Control loop compensation uses current mode feedback compensation entirely internally. This scheme allows bandwidth and phase margin to be almost independent of output capacitance and ESR

3.3V and 5V PWM Loop Compensation Fan 5233's 3.3V and 5V control loop functions as follows for voltage mode and current feedback stability. Each of them has an independent voltage feedback pin, as shown in Figure 1. They use voltage feedforward to guarantee loop rejection of input voltage changes: that is, the (pulse width modulation) ramp amplitude varies with the input voltage. Control loop compensation uses current mode feedback compensation entirely internally. This scheme allows bandwidth and phase margin to be almost independent of output capacitance and ESR. 3.3V and 5V PWM Current Limit The 3.3V and 5V converters detect their own low-side MOSFETs respectively to decide whether to enter current limit. If the output current exceeds the current measurement limit threshold, then the converter input pulse Iout is equal to the skip mode setting limit for overcurrent (OC). After 8 clock cycles, the regulator is locked (HSD and LSD off). in this case

, it will immediately trigger the undervoltage protection, again locking the regulator off after a 2µs delay (HSD and LSD off). The selection of the current limit setting resistor must include the tolerance of the current limit trip point, the MOSFET turn-on resistance and temperature coefficient, and the ripple current, in addition to the maximum output current. For example: the maximum DC output current of 5V is 5A, the input voltage is 16V, the MOSFET RDS, on is 17mΩ, and the current is 5A, the inductance is 5μH. Because of the RDS,on, the low-side MOSFET will have a maximum temperature (ambient + self-heating) of only 75°C at which its RDS,on increases to 20mΩ. The peak current is the DC output current plus the peak ripple current:

where T is the maximum period, VO is the output voltage, VIN is the input voltage and L is the inductance. This current produces a voltage on the low-side MOSFET of 7A•20mΩ=140mV. The current limit threshold is typically 150mV (135mV worst case) with R2 = 1KΩ, so this value applies. Type R2 is considered necessary if additional noise margin can be increased by another 10%. Precision Current Limiting Precision current limiting can be achieved by placing a discrete sense resistor between the low-side power MOSFET and ground. In this case, the current limit accuracy is determined by the IC, +10%.

Shutdown (SDWN) The SDWN pin shuts down all 4 converters (+5V, +3.3V, and +12V, 5V- always) and puts the fan 5233 in low power mode (shutdown mode). This mode of operation means using a button to switch between SDWN and VIN. Pressing the button allows (for the duration of the contact) to power the 5V-ALWAYS long enough for the microgram to power up and in turn latch the SDWN pin high. Once SDWN is high, the main regulator voltage goes high if the corresponding SDN3.3 and SDN5. Main 3.3V and 5V Soft Start, Sequencing and Standby Soft start of 3.3V and 5V converters is provided by an external capacitor between pin SDN3.3 (SDN5) and ground. If both SDWN and SDN3.3(SDN5) are high, if one of SDWN is off or SDN3.3(SDN5) is low. Standby mode means V power is off and V- is always on (SDWN=1 and SDN3.3=SDN5=0). Forced PWM Mode In any case, the controller can be forced to remain in PWM mode by setting FPWM to a high load condition. It is recommended to drive the FPWM high during power-up to ensure that the regulator turns on and controls the output capacitor inrush current by limiting the maximum duty cycle. Always run mode If 5V-always on is required, the SDWN pin must be permanently connected to the VIN. Here is that every time there is power, there will be a regulator. The state of the main regulator can be controlled through SDN5 and SDN3.3 pins.

3.3V and 5V Light Load Mode The 3.3V and 5V converters are synchronous bucks and can operate in two quadrants, which means that the ripple current is constant and independent of the load current. At light loads, this ripple current translates into low efficiency due to the circulating current losses that result in the mosfet. To optimize the efficiency at light load, then, FAN5233 switches from normal operation to special light load mode after 8 clock pulse delay. This prevents false triggering when the voltage on the on-state low-side MOSFET is positive. Vice versa, the FAN5233 switches back to PWM operation when the voltage becomes negative. The current threshold for light load switching is therefore: ys = iriplepic. In light load mode, the fan 5233 switches from PWM (pulse width modulation) to PFM (pulse frequency modulation), reducing the gate drive current. Transitioning to RFM inhibits mode by pulling the FPWM pin high. When the load current becomes smaller, the fan 5233 starts to work pulse skipping, but keeps in sync with the clock. See the next section on low-end drive management. Low-Side Driver Light Load Force During light-load operation, the low-side driver (LSD) is traditionally turned off permanently to avoid current reversal in the inductor and associated efficiency loss. At the same time, it is also necessary to turn on the low side driver sequence to a) measure the current (the current driver is sensed on the low side) and b) ensure that the charge pump is functioning properly, especially at low current and low input voltage conditions.

To do all of the above, when the circuit enters hysteretic operation, the LSD remains "on" to recycle the positive and decaying currents (corresponding to the negative voltage drop across the low-side driver Rdson), and turns off once the current crosses zero (corresponding to the drop zero-crossing Rdson becomes positive). Low profile drivers here for "partial duty cycle" or "active zero drop diodes" (with LSD being permanently off) allow more functionality without losing efficiency. 3.3V Voltage Regulation The output voltage of the 3.3V converter can be up to 10% by inserting a resistor divider in the feedback. The feedback impedance is about 66KΩ. So, for example, to increase the 3.3V output by 10%, use a 2.21KΩ/33.2KΩ voltage divider. Note that the output of the 5V regulator cannot be adjusted. The feedback line of the 5V regulator is used internally as the 5V supply, so cannot tolerate any impedance in series with it. 3.3V and 5V main overvoltage protection When the output voltage of the 3.3V (or 5V) converter exceeds 115% of the nominal value, the converter enters the overvoltage protection mode to protect the load from damage. During operation, a dump or short circuit of the MOSFET on a heavy load can cause the output voltage to be significantly higher than the normal operating range without circuit protection. When the output exceeds the overvoltage threshold, the overvoltage comparator forces the low gate driver high and turns on the low MOSFET. This will pull down the output voltage, which will eventually fuse the battery. Once the output voltage drops to the threshold, the OVP comparator turns off. The OVP scheme also provides a soft crowbar function (bang control followed by a fuse blow) that helps with severe load transients, but does not reverse the output voltage when activated, a common problem with OVPs lock plan. The prevention of output inversion does not require a Schottky diode to pass through the load.

3.3V and 5V undervoltage protection

Both converters are under-voltage (UV) protected when the output voltage of 3.3V or 5V drops below 75% of nominal, after a 2usec delay. In undervoltage protection, the high-side and low-side MOSFETs are turned off. Once triggered, the undervoltage protection remains on until power is cycled or the SDWN pin is reset. 12V Architecture The 12V converter is a traditional non-isolated flyback (also known as a "boost" converter). The input voltage to the converter is the +5V switcher output, so +12V can only be present if +5V is present. Also, if the external MOSFET is off, the output of the +12V converter is +5V, not zero. In turn will provide a non-zero output for the 12V regulator. To completely turn off the 12V regulator, an external P-channel MOSFET or LDO regulator with switching control can be used. If the LDO uses 12V, the boost should use an external resistor to set the converter to 13.2V to split the network. If not using a 12V "boost" converter, connect VFB12 (pin 15) to 5V - always (pin 6). The 12V loop compensated 12V converter should operate in discontinuous conduction mode. In this mode, if a capacitor with an appropriate ESR value is selected. 68 cubic feet of tantalum with a ripple current rating of 500mA, 95mΩ is recommended here. 12V Protection The 12V converter is protected against overvoltage. If the 12V feedback is 10–15% higher than the nominal value, the comparator forces the MOSFET off until the voltage falls below the comparator threshold. The 12V converter is also protected against overcurrent. If the short circuit pulls the output below 9V, all switching converters go into UV protection after a 2 microsecond delay. UV protection, all mosfets are off. Once the UV protection is triggered, it will remain on until the input power is recycled or the SDWN is reset. 12V Soft Start and Sequencing The 12V output starts simultaneously with the 5V output. A softly rising 5V output automatically produces a softly rising 12V output. The duty cycle of the 12V PWM is limited to prevent excessive current consumption. The voltage of the 12V supply must be higher than the UVLO limit (9V) (3.75V) when 5V is above its UVLO to avoid soft start.

5V-Always-On 5V-ALWAYS power is supplied by the on-chip linear regulator or via the VFB pin of the 5V switching power supply via an internal switch. 5V - Always power should be separated from ground using a 10µF capacitor. When the 5V switching power supply is turned off, or its output voltage is not within tolerance, the 5V-ALWAYS switch is turned on and the linear regulator is turned on. When the 5V switching power supply is running and the output voltage is within the specified range, the linear regulator is turned off, and the switch is turned on. The switch has a sufficiently low resistance 5V at maximum current draw - always powered and the output voltage regulated within spec. The purpose of the main power supply is to provide backup power for system microcontrollers (class 8051) and other integrated circuits that require backup power. The microcontroller as well as another integrated circuit can operate from the mains supply. 5V-Always protected 5V linear regulators are current-limited and under-voltage protected. Once the protection is triggered, the output is turned off until power is cycled or the SDWN is reset. Power is good when both PWM Buck converters are above the specified threshold. No other regulator is monitored by force very well. At least 10 microseconds (TW) when the mood is low. See Fig.

The error amplifier output voltage is clamped during load transients, allowing the error amplifier voltage to advance at full speed. After two clock cycles, if the amplifier is still out of voltage range, the duty cycle (DC) is clamped. The DC clamp automatically limits overcurrent under abnormal conditions, including short circuits:

Thermal Shutdown If the die temperature of the fan 5233 exceeds a safe limit, the IC shuts down automatically. When the over temperature (OT) event ends, the IC resumes normal operation. There is a 25°C thermal hysteresis between shutdown and startup.