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FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
May 2008
FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
Features
6A Output Current Over 95% Efficiency Fully Synchronous Operation with Integrated Schottky Diode on Low-side MOSFET Boosts Efficiency Programmable Frequency Operation: 200KHz to 600KHz Power-good Signal Accepts Ceramic Capacitors on Output External Compensation for Flexible Design Wide Input Range: 3V to 24V Output Voltage Range: 0.8V to 90% VIN Input Under-voltage Lockout Programmable Current Limit Under-voltage, Over-voltage, and Thermal Protections 5x6mm, 25-pin, 3-pad MLP
Description
The FAN2106 TinyBuckTM is an easy-to-use, cost and space-efficient, 6A synchronous buck solution. It enables designers to solve high current requirements in a small area with minimal external components. External compensation, programmable switching frequency, and current limit features allow for design optimization and flexibility. The summing current mode modulator uses lossless current sensing for current feedback and over-current, and includes voltage feedforward. Fairchild's advanced BiCMOS power process combined with low-RDS(ON) internal MOSFETs and a thermally efficient MLP package provide the ability to dissipate high power in a small package. Output over voltage, under voltage, and thermal shutdown protections help protect the device from damage during fault conditions.
Related Application Notes
AN-6033 -- FAN2106 Design Guide
Applications
Graphics Cards Battery-powered Equipment Set-top Boxes Point-of-load Regulation Servers
Ordering Information
Part Number
FAN2106MPX FAN2106EMPX
Operating Temperature Range
-10C to 85C -40C to 85C
Package
Molded Leadless Package (MLP) 5x6mm Molded Leadless Package (MLP) 5x6mm
Eco Status Packing Method
Green Green Tape and Reel Tape and Reel
For Fairchild's definition of "green" please visit: http://www.fairchildsemi.com/company/green/rohs_green.html.
(c) 2006 Fairchild Semiconductor Corporation FAN2106 Rev. 1.0.8
www.fairchildsemi.com
FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
Typical Application Diagram
Figure 1. Typical Application
Block Diagram
Figure 2. Block Diagram
(c) 2006 Fairchild Semiconductor Corporation FAN2106 Rev. 1.0.8
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FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
Pin Configuration
Figure 3. MLP 5x6mm Pin Configuration (Bottom View)
Pin Definitions
Pin #
P1, 6-12 P2, 2-5 P3, 21-23 1 13 14 15 16 17 18 19 20 24 25
Name
SW VIN PGND BOOT PGOOD EN VCC AGND ILIM R(T) FB COMP NC RAMP
Description
Switching Node. Power Input Voltage. Connect to the main input power source. Power Ground. Power return and Q2 source. High-Side Drive BOOT Voltage. Connect through capacitor (CBOOT) to SW. The IC includes an internal synchronous bootstrap diode to recharge the capacitor on this pin to VCC when SW is LOW. Power-Good Flag. An open-drain output that pulls LOW when FB is outside a 10% range of the reference. PGOOD does not assert HIGH until the fault latch is enabled. ENABLE. Enables operation when pulled to logic HIGH or left open. Toggling EN resets the regulator after a latched fault condition. This input has an internal pull-up when the IC is functioning normally. When a latched fault occurs, EN is discharged by a current sink. Input Bias Supply for IC. The IC's logic and analog circuitry are powered from this pin. Analog Ground. The signal ground for the IC. All internal control voltages are referred to this pin. Tie this pin to the ground island/plane through the lowest impedance connection. Current Limit. A resistor (RILIM) from this pin to AGND can be used to program the currentlimit trip threshold lower than the default setting. Oscillator Frequency. A resistor (RT) from this pin to AGND sets the PWM switching frequency. Output Voltage Feedback. Connect through a resistor divider to the output voltage. Compensation. Error amplifier output. Connect the external compensation network between this pin and FB. No Connect. This pin is not used. Ramp Amplitude. A resistor (RRAMP) connected from this pin to VIN sets the ramp amplitude and provides voltage feedforward functionality.
(c) 2006 Fairchild Semiconductor Corporation FAN2106 Rev. 1.0.8
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FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
Absolute Maximum Ratings
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only.
Parameter
VIN to PGND VCC to AGND BOOT to PGND BOOT to SW SW to PGND All other pins Continuous AGND = PGND
Conditions
Min.
Max.
28 6 35
Unit
V V V V V V V
-0.3 -0.5 -5 -0.3 Transient (t < 20ns, f < 600KHz)
6.0 24.0 30 VCC+0.3
Recommended Operating Conditions
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not recommend exceeding them or designing to absolute maximum ratings.
Symbol
VCC VIN TA TJ
Parameter
Bias Voltage Supply Voltage Ambient Temperature Junction Temperature
Conditions
VCC to AGND VIN to PGND FAN2106M FAN2106EM
Min.
4.5 3 -10 -40
Typ.
5.0
Max.
5.5 24 +85 +85 +125
Unit
V V C C C
Thermal Information
Symbol
TSTG TL TVP TI JC J-PCB PD Storage Temperature Lead Soldering Temperature, 10 Seconds Vapor Phase, 60 Seconds Infrared, 15 Seconds P1 (Q2) Thermal Resistance: Junction-to-Case P2 (Q1) P3 Thermal Resistance: Junction-to-Mounting Surface Power Dissipation, TA = 25C 4 7 4 35
(1)
Parameter
Min.
-65
Typ.
Max.
+150 +300 +215 +220
Unit
C C C C C/W C/W C/W C/W
2.8
(1)
W
Note: 1. Typical thermal resistance when mounted on a four-layer, two-ounce PCB, as shown in Figure 25. Actual results are dependent on mounting method and surface related to the design.
(c) 2006 Fairchild Semiconductor Corporation FAN2106 Rev. 1.0.8
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FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
Electrical Specifications
Recommended operating conditions are the result of using the circuit shown in Figure 1 unless otherwise noted.
Parameter
Power Supplies VCC Current
Conditions
SW = Open, FB = 0.7V, VCC = 5V, fSW = 600KHz Shutdown: EN = 0, VCC = 5V Rising VCC Hysteresis RT = 50K RT = 24K
Min.
Typ.
Max.
Unit
8 7 4.1 4.3 300 255 540 300 600 50
12 10 4.5
mA A V mV
VCC UVLO Threshold Oscillator Frequency Minimum On-Time
(2)
345 660 65
KHz KHz ns V
Ramp Amplitude, pk-pk Minimum Off-Time Reference Reference Voltage (VFB) (See Figure 4 for Temperature Coefficient) Error Amplifier DC Gain
(2) (2) (2)
16VIN, 1.8VOUT, RT = 30K, RRAMP = 200K
0.53 100 150 806 805
ns mV mV
FAN2106M, 25C FAN2106EM, 25C
794 795
800 800
80 VCC = 5V VCC = 5V, VCOMP = 2.2V VCC = 5V, VCOMP = 1.2V VFB = 0.8V, 25C RILIM Open 12 0.4 1.5 0.8 -850 6 -11 Internal IC Temperature 2 Consecutive Clock Cycles 16 Consecutive Clock Cycles Measured at FB Pin Measured at FB Pin (VFB ~500mV) 110 68
85 15 3.2 2.2 1.2 -650 8 -10 +155 +30 115 73 250 250 5.3 6.7 120 78 -450 10 -9
dB MHz V mA mA nA A A C C %VOUT %VOUT mV mV ms ms
Gain Bandwidth Product Output Voltage (VCOMP)
Output Current, Sourcing Output Current, Sinking FB Bias Current Protection and Shutdown Current Limit ILIM Current Over-Temperature Shutdown Over-Temperature Hysteresis Over-Voltage Threshold Under-Voltage Shutdown Fault Discharge Threshold Fault Discharge Hysteresis Soft-Start VOUT to Regulation (T0.8) Fault Enable/SSOK (T1.0)
Frequency = 600KHz
Note: 2. Specifications guaranteed by design and characterization; not production tested.
(c) 2006 Fairchild Semiconductor Corporation FAN2106 Rev. 1.0.8
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FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
Electrical Specifications (Continued)
Recommended operating conditions are the result of using the circuit shown in Figure 1 unless otherwise noted.
Parameter
Control Functions EN Threshold, Rising EN Hysteresis EN Pull-Up Resistance EN Discharge Current FB OK Drive Resistance PGOOD Threshold (Compared to VREF) PGOOD Output Low FB < VREF FB > VREF IOUT < 2mA
Conditions
Min.
Typ.
1.35 250 800
Max.
2.00
Unit
V mV K A
Auto-restart mode -14 +7
1 800 -11 +10 -8 +13 0.4
%VREF %VREF V
(c) 2006 Fairchild Semiconductor Corporation FAN2106 Rev. 1.0.8
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FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
Typical Characteristics
1.010 1.005 V FB 1.000 0.995 0.990 -50 0 50 Temperature (oC) 100 150
1.20 1.10 I FB 1.00 0.90 0.80 -50 0 50 Temperature (oC) 100 150
Figure 4. Reference Voltage (VFB) vs. Temperature, Normalized
Figure 5. Reference Bias Current (IFB) vs. Temperature, Normalized
1500 1200 900 600 300 0 0 20 40 60 80 100 120 140 RT (K)
1.02 1.01 Frequency
Frequency (KHz)
600KHz
1.00
300KHz
0.99 0.98 -50 0 50 Temperature ( C)
o
100
150
Figure 6. Frequency vs. RT
Figure 7.
Frequency vs. Temperature, Normalized
1.60 1.40
I ILIM
1.04 1.02 1.00 0.98 0.96
RDS
1.20 1.00 0.80 0.60 -50 0 50 Temperature ( C)
o
Q1 ~0.32 %/ C Q2 ~0.35 %/ C
100 150
o
o
-50
0
50 Temperature ( C)
o
100
150
Figure 8. RDS vs. Temperature, Normalized (VCC = VGS = 5V)
Figure 9.
ILIM Current (IILIM) vs. Temperature, Normalized
(c) 2006 Fairchild Semiconductor Corporation FAN2106 Rev. 1.0.8
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FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
Application Circuit
Figure 10. Application Circuit: 1.8VOUT, 500KHz
Typical Performance Characteristics
Typical operating characteristics using the circuit shown in Figure 10. VIN=16V, VCC=5V, unless otherwise specified.
100 95
Dissipation (mW) 1400 1200 1000 800 600 400 200 0
Efficiency (%)
90 85 80 75 70 0 1 2 3 Load (A) 4 5 6
8VIN 12VIN 18VIN
8VIN 12VIN 18VIN
0
1
2
3 Load (A)
4
5
6
Figure 11.
100 95 Efficiency (%)
1.8VOUT Efficiency Over VIN vs. Load
Figure 12. 1.8VOUT Dissipation Over VIN vs. Load
100 95 Efficiency (%) 90 85 80 75 70
90 85 80 75 70 0 1 2 3 Load (A) 4 5 6
8VIN, 300KHz 12VIN, 500KHz 18VIN, 700KHz
VIN=12V 300KHz 500KHz 700KHz
0
1
2
3 Load (A)
4
5
6
Figure 13. 1.8VOUT Efficiency Over Frequency vs. Load (Circuit Value Changes)
Figure 14. 3.3VOUT Efficiency vs. Load (Circuit Value Changes)
(c) 2006 Fairchild Semiconductor Corporation FAN2106 Rev. 1.0.8
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FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
Typical Performance Characteristics (Continued)
Typical operating characteristics using the circuit shown in Figure 10. VIN=16V, VCC=5V, unless otherwise specified.
VOUT
VOUT SW
SW
Figure 15. SW and VOUT Ripple, 6A Load
Figure 16. Start up with 1V Pre-Bias on Vout
VOUT EN IOUT SW
Figure 17. Transient Response, 2-6A Load
Figure 18.
Re-start on Fault
VOUT
VOUT
PGOOD
PGOOD EN
EN
Figure 19. Start-Up, 3A Load
Figure 20.
Shutdown, 3A Load
(c) 2006 Fairchild Semiconductor Corporation FAN2106 Rev. 1.0.8
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FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
Circuit Description
Application Note AN-6033 -- FAN2106 Design Guide includes a spreadsheet design aid to calculate external component values and verify loop stability given the following inputs: Output voltage Input voltage range Maximum output load current Maximum load transient current and maximum allowable output drop during load transient Maximum allowable output ripple Desired switching frequency Download AN-6033 -- FAN2106 Design Guide at: http://www.fairchildsemi.com/an/AN/AN-6033.pdf The regulator does not allow the low-side MOSFET to operate in full synchronous rectification mode until internal SS ramp reaches 95% of VREF (~0.76V). This helps the regulator to start on a pre-biased output and ensures that inductor current does not "ratchet" up during the soft-start cycle. VCC UVLO or toggling the EN pin discharges the SS and resets the IC.
Bias Supply
The FAN2106 requires a 5V supply rail to bias the IC and provide gate-drive energy. Connect a 1.0f X5R or X7R decoupling capacitor between VCC and PGND. Since VCC is used to drive the internal MOSFET gates, supply current is frequency and voltage dependent. Approximate VCC current (ICC) can be calculated using:
Initialization
Once VCC exceeds the UVLO threshold and EN is HIGH, the IC checks for an open or shorted FB pin before releasing the internal soft-start ramp (SS). If R1 is open (Figure 1), the error amplifier output (COMP) is forced LOW and no pulses are generated. After the SS ramp times out (T1.0), an under-voltage latched fault occurs. If the parallel combination of R1 and RBIAS is 1K, the internal SS ramp is not released and the regulator does not start.
ICC ( mA ) = 4.58 + [(
VCC - 5 + 0.013) * ( f - 128 )] 227
(1)
where frequency (f) is expressed in KHz.
Setting the Output Voltage
The output voltage of the regulator can be set from 0.8V to 80% of VIN by an external resistor divider (R1 and RBIAS in Figure 1). The internal reference is 0.8V with 650nA, sourced from the FB pin to ensure that, if the pin is open, the regulator does not start. The external resistor divider is calculated using:
- 0 .8 V V 0 .8 V = OUT + 650nA RBIAS R1
Soft-Start
Once internal SS ramp has charged to 0.8V (T0.8), the output voltage is in regulation. Until SS ramp reaches 1.0V (T1.0), the "Fault Latch" is inhibited. To avoid skipping the soft-start cycle, it is necessary to apply VIN before VCC reaches its UVLO threshold. Soft-start time is a function of oscillator frequency.
EN 1.35V
2400 CLKs
(2)
Connect RBIAS between FB and AGND.
Setting the Frequency
Oscillator frequency is determined by an external resistor, RT, connected between the R(T) pin and AGND:
0.8V
f(KHz ) =
FB
1.0V 0.8V Fault Latch Enable
10 6 ( 65 * R T ) + 135
(3)
where RT is expressed in K.
R T ( K ) =
SS
3200 CLKs
(10 6 / f ) - 135 65
(4)
where frequency (f) is expressed in KHz.
T0.8
4000 CLKs
The regulator can not start if RT is left open.
T1.0
Figure 21. Soft-Start Timing Diagram
(c) 2006 Fairchild Semiconductor Corporation FAN2106 Rev. 1.0.8 www.fairchildsemi.com 10
FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
Calculating the Inductor Value
Typically the inductor is set for a ripple current (IL) of 10% to 35% of the maximum DC load. Regulators requiring fast transient response use a value on the high side of this range, while regulators that require very low output ripple and/or use high-ESR capacitors restrict allowable ripple current:
Loop Compensation
The loop is compensated using a feedback network around the error amplifier. Figure 22 shows a complete Type-3 compensation network. For Type-2 compensation, eliminate R3 and C3.
IL =
VOUT * (1 - D) L*f
(5)
where f is the oscillator frequency and:
L=
VOUT * (1 - D) IL * f
(6)
Setting the Ramp Resistor Value
The internal ramp voltage excursion (VRAMP) during tON should be set to 0.6V. RRAMP is approximately: Figure 22. Compensation Network Since the FAN2106 employs summing current-mode architecture, Type-2 compensation can be used for many applications. For applications that require wide loop bandwidth and/or use very low-ESR output capacitors, Type-3 compensation may be required. The AN-6033 spreadsheet calculator can be used to calculate these component values.
RRAMP(K )
( V - 1.8) * VOUT = IN -6 -2 18 x10 * VIN * f
(7)
where frequency (f) is expressed in KHz.
Setting the Current Limit
The FAN2106 uses its internal low-side MOSFET for current-sensing. The current-limit threshold voltage (VILIM) is compared to a scaled version of the voltage drop across the low-side MOSFET, sampled at the end of each PWM off-time/cycle. The default threshold (ILIM open) is temperature compensated. The 10A current sourced from the ILIM pin can be used to establish a lower, temperature-dependent, current-limit threshold by connecting an external resistor (RILIM) to AGND:
RILIM(K) = 0.45 * RDS * K T * (IOUT - IL ) + 142.5 2
Protection
The converter output is monitored and protected against extreme overload, short-circuit, over-voltage, under-voltage, and over-temperature conditions. An internal "Fault Latch" is set for any fault intended to shut down the IC. When the fault latch is set, the IC discharges VOUT by enhancing the low-side MOSFET until FB<0.25V. The MOSFET is not turned on again unless FB>0.5V. This behavior discharges the output without causing undershoot (negative output voltage).
(8)
0.25/0.5V FB
FAULT PWM GATE DRIVE PWM LATCH
where: I = desired current limit set point in Amps, RDS is expressed in m, KT = the normalized temperature coefficient of the low-side MOSFET (Q2) from Figure 8. After 16 consecutive, pulse-by-pulse, current-limit cycles, the fault latch is set and the regulator shuts down. Cycling VCC or EN restores operation after a normal soft-start cycle (refer to Auto-Restart section). The over-current protection fault latch is active during the soft-start cycle. In case RILIM is not connected, the IC uses internal default current limit threshold.
Figure 23. Latched Fault Response
Under-Voltage Shutdown
If voltage on the FB pin remains below the undervoltage threshold for 16 consecutive clock cycles, the fault latch is set and the converter shuts down. This protection is not active until the internal SS ramp reaches 1.0V during soft start.
Over-Voltage Protection / Shutdown
If voltage on the FB pin exceeds the over-voltage threshold for two consecutive clock cycles, the fault latch is set and shutdown occurs.
(c) 2006 Fairchild Semiconductor Corporation FAN2106 Rev. 1.0.8
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FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
A shorted high-side MOSFET condition is detected when SW voltage exceeds ~0.7V while the low-side MOSFET is fully enhanced. The fault latch is set immediately upon detection. The two fault protection circuits above are active all the time, including during soft-start.
Over-Temperature Protection
The chip incorporates an over-temperature protection circuit that sets the fault latch when a die temperature of about 150C is reached. The IC restarts when the die temperature falls below 125C.
Auto-Restart
After a fault, EN pin is discharged by a 1A current sink to a 1.1V threshold before the 800K pull-up is restored. A new soft-start cycle begins when EN charges above 1.35V. Depending on the external circuit, the FAN2106 can be configured to remain latched-off or to automatically restart after a fault. Table 1. Fault / Restart Provisioning EN pin Pull to GND VCC Open Cap to GND Controller / Restart State OFF (disabled) No restart - latched OFF(After VCC comes up) Immediate restart after fault New soft-start cycle after: tDELAY (ms) = 3.9 * C(nf)
Power Good (PGOOD) Signal
PGOOD is an open-drain output that asserts LOW when VOUT is out of regulation, as measured at the FB pin. Thresholds are specified in the Electrical specifications section. PGOOD does not assert HIGH until the fault latch is enabled (T1.0).
PCB Layout
With EN left open, restart is immediate. If auto-restart is not desired, tie the EN pin to the VCC pin or pull it high after VCC comes up with a logic gate to keep the 1A current sink from discharging EN to 1.1V. Figure 25. Recommended PCB Layout
Figure 24.
Fault Latch with Delayed Auto-Restart
(c) 2006 Fairchild Semiconductor Corporation FAN2106 Rev. 1.0.8
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FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
Physical Dimensions
2X
TOP VIEW
2X RECOMMENDED LAND PATTERN ALL VALUES TYPICAL EXCEPT WHERE NOTED
SIDE VIEW
SEATING PLANE
A) DIMENSIONS ARE IN MILLIMETERS. B) DIMENSIONS AND TOLERANCES PER ASME Y14.5M, 1994 C) DIMENSIONS DO NOT INCLUDE MOLD FLASH OR BURRS. D) DESIGN BASED ON JEDEC MO-220 VARIATION WJHC E) TERMINALS ARE SYMMETRICAL AROUND THE X & Y AXIS EXCEPT WHERE DEPOPULATED. F) DRAWING FILENAME: MKT-MLP25AREV2
BOTTOM VIEW
Figure 26. 5x6mm Molded Leadless Package (MLP)
Package drawings are provided as a service to customers considering Fairchild components. Drawings may change in any manner without notice. Please note the revision and/or date on the drawing and contact a Fairchild Semiconductor representative to verify or obtain the most recent revision. Package specifications do not expand the terms of Fairchild's worldwide terms and conditions, specifically the warranty therein, which covers Fairchild products. Always visit Fairchild Semiconductor's online packaging area for the most recent package drawings: http://www.fairchildsemi.com/packaging/
(c) 2006 Fairchild Semiconductor Corporation FAN2106 Rev. 1.0.8
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FAN2106 -- TinyBuckTM 6A, 24V Input, Integrated Synchronous Buck Regulator
(c) 2006 Fairchild Semiconductor Corporation FAN2106 Rev. 1.0.8
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