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FAN5232
Adjustable PWM Buck Controller for LCD PCs
Features
* Three outputs: Adjustable Buck, 3.3V-Always, 5V-Always * Adjustable synchronous switcher, 5V - 80% Vin * 1% internal reference precision * Current mode with voltage feed-forward * Precision current limit option * Charge pump works at all loads * No shoot-through current * Independent shutdown pins for ACPI * Power Good, input UVLO, output OV * 5.6V to 24V input voltage range
Description
The FAN5232 is a high efficiency and high precision DC/DC controller for PCs. It has a synchronous switcher whose output can be adjusted from 5V up to 80% of Vin. It also has two linear regulators for standby, 3.3V and 5V. The PWM utilizes both input and output voltage feedback in a current-mode control, allowing for fast and stable loop response over a wide range of input and output variations. Synchronous switching provides best efficiency over a wide range of loads. Current sense based on MOSFET RDS,on gives maximum efficiency, while also permitting use of an optional sense resistor for high precision. The FAN5232 is available in a 14 pin TSSOP package.
Applications
* LCD PCs * Notebook PCs and PDAs * Hand-held portable instruments
Block Diagram
Vin = 16-22V
1 3.3V-Always 5V-Always 2 3 FAN5232 4 SDWN SDNADJ PWRGD 5 6 7
14 13 12 11 10 9 8 + 12V @ 8A
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FAN5232
PRODUCT SPECIFICATION
Pin Assignments
VBATT 3V_ALWAYS 5V_ALWAYS AGND SDWN SDNADJ PWRGD 1 2 3 4 5 6 7 14 13 12 11 10 9 8 CPUMP HSD ISNS SW LSD PGND VFB
Pin Description
Pin Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Pin Name VBATT 3V_ALWAYS 5V_ALWAYS AGND SDWN SDNADJ PWRGD VFBSW PGND LSD SW ISNS HSD CPUMP Pin Function Description Battery Voltage. Battery voltage sensor. 3.3V-ALWAYS Linear Regulator. Total load current on pins 2 and 3 together must not exceed 50mA. 5V-ALWAYS Linear Regulator. Total load current on pins 2 and 3 together must not exceed 50mA. Analog Ground. IC Shutdown. Puts entire chip into shutdown. OFF=0. ON=1. Shutdown and Softstart for the Switcher. OFF=0. ON=1. Switcher Output OK. An open collector output that will be low if the switcher output is out of spec. Voltage Feedback for the Switcher. Ground for the Switcher. Connect by the shortest possible path to the source of the low side MOSFET. Low Side FET Driver for the Switcher. Connect this pin through a resistor to the gate of an N-channel MOSFET. High Side FET Source and Low Side FET Drain Switching Node. Current Feedback for the Switcher. Connect by the shortest possible path to a resistor connected to the drain of the low side MOSFET. High Side FET Driver for the Switcher. Connect this pin through a resistor to the gate of an N-channel MOSFET. Charge Pump for the Switcher. Generates gate drive voltage for the high-side MOSFET.
Absolute Maximum Ratings1
Parameter VBATT Pin PHASE, IFB, SDWN Pins CPUMP, HSD Pins All Other Pins Thermal Resistance, J-A J-C Junction Temperature Storage Temperature Lead Temperature, Soldering 10 sec. -65 Conditions Min. -0.3 -5 -0.3 -0.3 100 32 150 150 300 Typ. Max. 29 29 34 6.5 Units V V V V C/W C/W C C C
Note: 1. Functional operation under any of these conditions is NOT implied. Performance and reliability are guaranteed only if Operating Conditions are not exceeded. 2 REV. 1.1.1 10/7/02
PRODUCT SPECIFICATION
FAN5232
Recommended Operating Conditions
Parameter VBATT Voltage Ambient Temperature Conditions Min. 5.6 -20 Typ. Max. 24 85 Units V C
Electrical Specifications
(VBATT = 16V, TA = -20 to 85C, circuit of Figure 1, unless otherwise specified.) Parameter Supply VCC Input Quiescent Current
H/LSD Open
Conditions
Min.
Typ.
Max. 1.4 60 10
Units mA A A V
Stand-by Shut-down VCC Input UVLO Threshold Switcher Output Voltage Precision, VFB Oscillator Frequency, fOSC Gate Drive On-Resistance for all Sources and HSD Sinks Gate Drive On Resistance for LSD Sink HSD On Output, VCPUMP-VGS HSD Off Output, VGS LSD Off Output, VGS Ramp Amplitude, pk-pk Ramp Offset Ramp Gain from VBATT Error Amplifier GBW Current Limit Threshold Over Voltage Threshold Under Voltage Threshold Max Duty Cycle Min HSD On-time VFBSW, ISNS Input Leakage Current SDN/SS Full On Voltage Min. SDN/SS Full Off Voltage Max. 5V and 3.3V Always Linear Regulator Accuracy Rated Output Current Overcurrent Limit Undervoltage Threshold
REV. 1.1.1 10/7/02
Rising Falling 0.1 I 5.5A, 7.2 VBATT 24V I 100mA, 5.6 VBATT 24V
4.3 4.0 4.900 4.900 255
4.5 4.3 5 5 300 6 1.5
5.1 4.7 5.100 5.100 345 12 8 100 100 100 100
V KHz mV mV mV mV V V mV/V MHz
I = 10A I = -10A I = -10A 2 0.5 125 3 R3 = 1K 2s delay 2s delay 135 110 70 80 200 100 4.2 150 115 75
LSD On Output, V5V-Always-VGS I = 10A
165 120 80
mV %VO %VO % nsec
200
nA V
800 5.6V VBATT 22V, 0 ILOAD 50mA I3.3 + I5 2s delay 2s delay 100 70 75 -3.3 2 50 180 80
mV % mA mA %
3
FAN5232
PRODUCT SPECIFICATION
Electrical Specifications (Continued)
(VBATT = 16V, TA = -20 to 85C, circuit of Figure 1, unless otherwise specified.) Parameter Control and Signal Functions Control Logic Low Control Logic High Softstart Current Over-temperature Shutdown Over-temperature Hysteresis PWRGD Threshold PWRGD Saturation Voltage PWRGD Leakage Current PWRGD Pulse Width for Trip Isink = 4mA VCC = 5.5V Low High, High Low 5 -14 2 3 5 150 25 -12 -9 400 1 10 7 600 mV V A C C %VO mV A sec Conditions Min. Typ. Max. Units
Application Circuit
Vin = 16-22V
+ C1
1 C2 3.3V-Always 5V-Always C3 2 3 4 5 6 C4 PWRGD R1 5V 7 U1 FAN5232
14 R2 13 R3 12 Q1
D1 C5 12V @ 8A L1 + C6
11 10 R4 9 8 R6 Q2 R5
SDWN SDNADJ
Figure 1. Application Circuit for LCD PC Main Power
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REV. 1.1.1 10/7/02
PRODUCT SPECIFICATION
FAN5232
Table 1. RC5232 Application Bill of Materials
Reference C1 C2-5 C6 R1 R2, R4 R3, R5 R6 D1 L1 Q1 Q2 U1 Manufacturer, Part # SANYO 25SV47M Any AVX TPSE227M016#0100 Any Any Any Any Fairchild MBR0540L Coiltronics UP2B-1R5 Fairchild FDS6690A Fairchild FDS6680S Fairchild FAN5232 Quantity Description 1 4 1 1 2 2 1 1 1 1 1 1 47F, 25V 100nF, 50V 220F, 16V 10K, 1% 4.7, 1% 1K, 1% 715, 1% 500mA, 40V Schottky 1.5H, 8.3A 30V N-channel MOSFET 30V N-channel MOSFET with Integrated Schottky Controller R < 8m R = 20m @ VGS = 4.5V R = 17m @ VGS = 4.5V Comments OSCON, Irms = 3.5A Ceramic Tantalum, ESR=100m
Application Information
Overview
The FAN5232 is a high efficiency and high precision DC/DC controller for LCD PCs and portable applications. It provides a switcher controller capable of generating a voltage between 5V to 80% of Vin, and a 5V and a 3.3V linear regulator for standby applications. The controller has a power good output and an enable/soft start to permit proper system sequencing.
Shutdown
There are two separate shutdown pins to provide output power control - SDWN, and SDNADJ. Taking the SDNADJ pin low will disable the switcher output and reset the output's internal latches for short circuit, under-voltage and over-voltage. Taking the SDWN pin low puts the entire chip in shutdown. Each of the SDN pins has an internal pull-up.
Initialization
The FAN5232 automatically initializes upon receipt of input power. The Power-on Reset (POR) function continually monitors the input supply voltage on the VCC pin and initiates soft start operation after the input supply voltage exceeds 4.5V. Should this voltage drop below 4.0V, POR disables the chip.
Switcher Architecture
Overview
The switcher output of the FAN5232 is generated from the unregulated input (battery) voltage using a synchronous buck converter. Both high-side and low-side MOSFETs are N-channel. The converter has pins for current sensing using the low-side MOSFET RDS,on; a pin for voltage-sense feedback; a pin that enables the converter and permits soft-start; a power good pin; and a pin for generating the boost voltage to drive the high-side MOSFET.
Soft Start
When soft start is initiated by POR, and if the SDWN pin is not held low, the voltage on the SDNADJ pin begins ramping up, with the rate of rise set by the external capacitor on the pin. Below 700mV, the output is off. Between 700mV and 1.6V, the output is allowed to linearly ramp up. Above 1.6V, the output is fully enabled, and regulates.
REV. 1.1.1 10/7/02
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FAN5232
PRODUCT SPECIFICATION
Loop Compensation
The switcher regulator control loop of the FAN5232 is current-mode with voltage feed-forward. It uses voltage feed-forward to guarantee loop rejection of input voltage variation: the ramp amplitude is varied as a function of the input voltage. Compensation of the control loop is done entirely internally using current-mode compensation. This scheme allows the bandwidth and phase margin to be almost independent of output capacitance and capacitors' ESR. Use of a current sense resistor other than the recommended 1K may affect the converter's stability.
Precision Current Limit
Precision current limiting can be achieved by placing a discrete sense resistor between the source of the low-side MOSFET and ground. Sensing is then accomplished with the 1K resistor between the sense resistor and the IFBSW pin, as shown in Figure 2. In this case, current limit accuracy is set by the tolerance of the IC, 10%.
LSD ISNS
Current Sensing
Current sensing is done by measuring the voltage across the low side MOSFET 50nsec after it is turned on. This value is then held for current feedback and over-current limit. The gain is set by an external resistor from the drain to the ISNS pin, which is normally set to be 1K.
PGND
Figure 2. Precision Current Sensing
Current Limit
The converter senses the voltage across its low-side MOSFET to determine when to enter current limit. If output current in excess of the current limit threshold is measured, the converter enters pulse skip mode with Iout equal to the over-current (OC) limit. If this situation persists for 8 clock cycles then the regulator is latched off (HSD and LSD off). This is the likely scenario in case of a "soft" short. If the short is "hard", it will instantly trigger the under-voltage protection, which again will latch the regulator off (HSD and LSD off) after a 2sec delay. Selection of a current-limit set resistor must include the tolerance of the current-limit trip point, the MOSFET resistance and temperature coefficient, and the ripple current, in addition to the maximum output current. Example: Maximum DC output current on the 12V is 8A, the MOSFET RDS,on is 17m, and the inductor is 4.7H at a current of 8A. Because of the low RDS,on, the low-side MOSFET will have a maximum temperature (ambient + self-heating) of only 75C, at which its RDS,on increases to 24m. Peak current is DC output current plus peak ripple current:
TV O * ( V in - V o ) I pk I DC + ------------------------------------------2 * L * V in 4s * 12V * ( 19V - 12V ) = 8A + --------------------------------------------------------------- = 11A 2 * 4.7H * 12V
Softstart
Softstart of the switcher is accomplished by means of an external capacitor between pins SDNADJ and ground.
Overvoltage Protection (Soft Crowbar)
When the output voltage of the switcher exceeds approximately 115% of nominal, it enters into over-voltage (OV) protection, with the goal of protecting the load from damage. During operation, severe load dump or a short of an upper MOSFET can cause the output voltage to increase significantly over normal operation range. When the output exceeds the over-voltage threshold of 115%, the over-voltage comparator forces the lower gate driver high and turns the lower MOSFET on. This will pull down the output voltage and eventually may blow the battery fuse. As soon as output voltage drops below the threshold, the OVP comparator is disengaged. This OVP scheme provides a soft crowbar function (bangbang control followed by blow of the fuse), which helps to tackle severe load transients and does not invert the output voltage when activated - common problem for OVP schemes with a latch. The prevention of the output inversion saves the use of a Schottky diode across the load.
Undervoltage Protection
When the output voltage of the switcher falls below 75% of nominal value, after a 2usec delay it goes into under-voltage protection. In under-voltage protection, the high and low side MOSFETs are turned off. Once under-voltage protection is triggered, it remains on until power is recycled.
where T is the maximum period, VO is output voltage, Vin is input voltage, and L is the inductance. This current generates a voltage on the low-side MOSFET of 11A * 24m = 254mV. The current limit threshold is typically 150mV (worst-case 135mV) with R2 = 1K, and so this value must be decreased to (135/254) * 1K = 531.
5V/3.3V-ALWAYS Operation
The 5V-ALWAYS supply is generated from the on-chip linear regulator off the input supply voltage. The 3.3V-ALWAYS is generated from a linear regulator attached internally to the 5V-ALWAYS.
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PRODUCT SPECIFICATION
FAN5232
The purpose of these two supplies -whose combined current is specified to never exceed 50mA- is to provide power to the system micro-controller (8051 class) as well as a few other ICs needing a stand-by power. The micro-controller as well as the other IC's discussed here are migrating from 5V to 3.3V power at different times and we expect that some "legacy" devices will continue to need 5V indefinitely.
where Iout is the output current of the converter, and DC is the duty cycle, DC = Vin / Vout. Capacitor ripple current rating is a function of temperature and switching frequency, and so the manufacturer should be contacted to find out the ripple current rating at the expected operational temperature and frequency.
Soft Start Capacitor selection 5V/3.3V-ALWAYS Protections
The two internal linear regulators are current limit and undervoltage protected. Once protection is triggered all outputs go off until power is recycled. The recommended value of the soft start capacitor is 100nF. This will result in roughly 20msec turn on time. The general formula is:
( I SS * T SS ) C SS = --------------------------1.125V
ALWAYS mode of Operation
If it is desired that the ALWAYS voltages are always ON then the SDWN pin must be connected to VCC permanently. This way the ALWAYS regulator comes up as soon as there is power while the state of the switcher can be controlled via the SDNADJ pin.
Where ISS is the soft start current (5A), TSS is the soft start delay (i.e. 20msec).
Control and Signal Circuitry Component Selection
Switcher MOSFET Selection
The application circuit shown in Figure 1 is designed to run with an input voltage operating range of 16-22V. This input range helps determine the selection of the MOSFETs for the switcher, since the high-side MOSFET can be on as much as (Vout / Vin) = 12V / 16V = 75% of the time, and the low-side MOSFET as much as 1 - (Vout / Vin) = 1 - (12V / 22V) = 45% of the time. The MOSFETs have maximum duty cycles greater than 45%. Thus, it is necessary to size both approximately the same.
Power Good
Power Good is an open-collector signal, and is asserted when the outputs are greater than 88% of nominal for more than 2sec. When PWRGD goes low it will stay low for at least 2sec.
Fault Handling
The FAN5232 has a full suite of protection against faults. Consult Table 2 for an overview, and the individual sections for details. Table 2. Fault Handling Fault Condition OC Switcher OC Always UV Switcher UV Always UV VCC Switcher Latch off No Change Latch off after 2sec No Change Off 3V- and 5V-Always No Change Ramp Down till UV No Change Latch off after 2sec Off
Switcher Schottky Selection
In the application shown in Figure 1, the use of a SynchFET eliminates the need of a Schottky diode for the synchronous buck. If SynchFETs are not used, selection of a schottky is determined by the maximum current at which the converter operates. Select a diode whose instantaneous Vf is less than 0.75V at the maximum output current. The schottky dissipates no power, because it is on for only a very small portion of the switching cycle.
Input Capacitor Selection
Input capacitor selection is determined by ripple current rating by the formula:
I rms = I out DC - DC
2
REV. 1.1.1 10/7/02
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FAN5232
PRODUCT SPECIFICATION
Mechanical Dimensions
14-Lead TSSOP
Symbol A A1 A2 B C D H E e L N ccc Inches Min. -- .002 .031 Max. .047 .006 .041 Millimeters Min. -- 0.05 0.80 Max. 1.20 0.15 1.05 5 5 2, 4 Notes: Notes 1. Dimensioning and tolerancing per ANSI Y14.5M-1982. 2. "D" and "E1" do not include mold flash. Mold flash or protrusions shall not exceed .010 inch (0.25mm). 3. "L" is the length of terminal for soldering to a substrate. 4. Terminal numbers are shown for reference only. 5. "B" & "C" dimensions include solder finish thickness. 6. Symbol "N" is the maximum number of terminals.
.007 .011 .004 .008 .252 .260 .252 BSC .169 .177 .026 BSC .018 .030 14 0 -- 8 .004
0.17 0.27 0.09 0.20 6.40 6.60 6.40 BSC 4.30 4.50 0.65 BSC 0.45 0.75 14 0 -- 8 0.10
3 6
D
E
H
A2 A1 SEATING PLANE e B -C- LEAD COPLANARITY ccc C L C
A
8
REV. 1.1.1 10/7/02
FAN5232
Ordering Information
Product Number FAN5232MTC Package 14 Lead TSSOP
DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, or (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.
www.fairchildsemi.com
10/7/02 0.0m 003 Stock#DS30005232 2001 Fairchild Semiconductor Corporation

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