Fairchild FAN2108 service manual

August 2009

FAN2108 — TinyBuck™

3-24V Input, 8A, High-Efficiency, Integrated Synchronous
Buck Regulator

FAN2108 — TinyBuck™, 3-24V Input, 8A, High-Efficiency, Integrated Synchronous Buck Regulator

Features

 Wide Input Voltage Range: 3V-24V
 Wide Output Voltage Range: 0.8V to 80% V

IN

 8A Output Current
 Programmable Frequency Operation: 200KHz to

600KHz

 Over 95% Peak Efficiency
 Integrated Schottky Diode on Low-side MOSFET

Boosts Efficiency

 Internal Bootstrap diode
 Power-Good Signal
 Pre-Bias Startup
 Accepts Ceramic Capacitors on Output
 External Compensation for Flexible Design
 Input Under-Voltage Lockout
 Programmable Current Limit
 Under-Voltage, Over-Voltage, and Thermal

Shutdown Protections

 Internal Soft-Start
 5x6mm, 25-Pin, 3-Pad MLP Package

Description

The FAN2108 TinyBuck™ is a highly efficient, small
footprint, 8A, synchronous buck regulator.

The FAN2108 contains both synchronous MOSFETs
and a controller/driver with optimized interconnects in
one package, which enables designers to solve high­current requirements in a small area with minimal
external components.

External compensation, programmable switching
frequency, and current limit features allow design
optimization and flexibility.

The summing current mode modulator uses lossless
current sensing for current feedback and over-current
protection. Voltage feedforward helps operation over a
wide input voltage range.

Fairchild’s advanced BiCMOS power process,
combined with low-R
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. FAN2108 prevents pre­biased output discharge during startup in point-of-load
applications.

internal MOSFETs and a

DS(ON)

Applications

Servers


 Point-of-Load Regulation

Related Application Notes

AN-8022 — TinyCalc™ Calculator

 High-End Computing Systems
 Graphics Cards
 Battery-Powered Equipment
 Set-Top Boxes

Ordering Information

Operating

Part Number

FAN2108MPX -10°C to 85°C Molded Leadless Package (MLP) 5x6mm Green Tape and Reel

FAN2108EMPX -40°C to 85°C Molded Leadless Package (MLP) 5x6mm Green Tape and Reel

For Fairchild’s definition of Eco Status, please vis it: http://www.fairchildsemi.com/company/green/rohs_green.html.

© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN2108 • Rev. 1.0.1

Temperature Range Package

Eco

Status

Packing

Method

Typical Application

FAN2108 — TinyBuck™, 3-24V Input, 8A, High-Efficiency, Integrated Synchronous Buck Regulator

Block Diagram

Figure 1. Typical Application Diagram

Figure 2. Block Diagram

© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN2108 • Rev. 1.0.1 2

Pin Configuration

FAN2108 — TinyBuck™, 3-24V Input, 8A, High-Efficiency, Integrated Synchronous Buck Regulator

Figure 3. MLP 5x6mm Pin Configuration (Bottom View)

Pin Definitions

Pin # Name Description

P1, 6-12 SW

P2, 2-5 VIN

P3, 21-23 PGND

1 BOOT

13 PGOOD

14 EN

15 VCC

16 AGND

17 ILIM

18 R(T)

19 FB

20 COMP

24 NC

25 RAMP

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 (C

includes an internal synchronous bootstrap diode to recharge the capacitor on this pin to
V

when SW is LOW.

CC

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 (R

limit trip threshold lower than the default setting.

Oscillator Frequency. A resistor (R

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 (R

and provides voltage feedforward functionality.

) to SW. The IC

BOOT

) from this pin to AGND can be used to program the current-

ILIM

) from this pin to AGND sets the PWM switching

T

) connected from this pin to VIN sets the ramp amplitude

RAMP

© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN2108 • Rev. 1.0.1 3

FAN2108 — TinyBuck™, 3-24V Input, 8A, High-Efficiency, 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 Conditions Min. Max. Unit

VIN to PGND 28 V

VCC to AGND AGND=PGND 6 V

BOOT to PGND 35 V

BOOT to SW -0.3 6.0 V

SW to PGND

All other pins -0.3 VCC+0.3 V

ESD

Continuous -0.5 24.0 V

Transient (t < 20ns, f <

Human Body Model, JEDEC JESD22-A114 2

600KHz) -5 30 V

kV

Charged Device Model, JEDEC JESD22-C101 2.5

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 Parameter Conditions Min. Typ. Max. Unit

VCC Bias Voltage VCC to AGND 4.5 5.0 5.5 V

VIN Supply Voltage VIN to PGND 3 24 V

TA Ambient Temperature

FAN2108MPX -10 +85 °C

FAN2108EMPX -40 +85 °C

TJ Junction Temperature +125 °C

f Switching Frequency 600 kHz

Thermal Information

Symbol Parameter Min. Typ. Max. Unit

T

Storage Temperature -65 +150 °C

STG

TL Lead Soldering Temperature, 10 Seconds +300 °C

TVP Vapor Phase, 60 Seconds +215 °C

TI Infrared, 15 Seconds +220 °C

P1 (Q2) 4 °C/W

θJC

θ

J-PCB

PD Power Dissipation, TA=25°C

Thermal Resistance: Junction-to-Case

Thermal Resistance: Junction-to-Mounting Surface

(1)

2.8 W

Note:

1. Typical thermal resistance when mounted on a four-layer, two-ounce PCB, as shown in Figure 24. Actual results
are dependent on mounting method and surface related to the design.

P2 (Q1) 7 °C/W

P3 4 °C/W

(1)

35 °C/W

© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN2108 • Rev. 1.0.1 4

Electrical Specifications

Electrical specifications are the result of using the circuit shown in Figure 1 unless otherwise noted.

Symbol Parameter Conditions Min. Typ. Max. Unit

Power Supplies

SW=Open, FB=0.7V, VCC=5V,
f

=600KHz

ICC VCC Current

V

VCC UVLO Threshold

UVLO

SW

Shutdown: EN=0, V

=5V 7 10 µA

CC

Rising VCC 4.1 4.3 4.5 V

Hysteresis 300 mV

Oscillator

f Frequency

tON Minimum On-Time

V

Ramp Amplitude, peak-to–peak

RAMP

t

Minimum Off-Time

OFF

(2)

(2)

50 65 ns

100 150 ns

RT=50KΩ

R

=24KΩ

T

16VIN, 1.8V
R

=200KΩ

RAMP

, RT=30KΩ,

OUT

Reference

VFB

Reference Voltage (see Figure 4 for

Temperature Coefficient)

FAN2108MPX, 25°C 794 800 806 mV

FAN2108EMPX, 25°C 795 800 805 mV

Error Amplifier

G DC Gain

BW Gain Bandwidth Product

V

Output Voltage

COMP

I

Output Current, Sourcing VCC=5V, V

SINK

I

Output Current, Sinking VCC=5V, V

SOURCE

I

FB Bias Current VFB=0.8V, 25°C -850 -650 -450 nA

BIAS

(2)

80 85 dB

(2)

12 15 MHz

V

=5V

CC

=2.2V 1.5 2.2 mA

COMP

=1.2V 0.8 1.2 mA

COMP

Protection and Shutdown

Open at 25°C (see Circuit

R

I

Current Limit

LIM

I

I

ILIM

T

Over-Temperature Shutdown +155 °C

TSD

T

HYS

V

OVP

V

UVLO

V

Fault Discharge Threshold Measured at FB Pin 250 mV

FLT

V

FLT_HYS

Current -11 -10 -9 µA

LIM

Over-Temperature Hysteresis

Over-Voltage Threshold Two Consecutive Clock Cycles 110 115 121 %V

Under-Voltage Shutdown 16 Consecutive Clock Cycles 68 73 78 %V

Fault Discharge Hysteresis Measured at FB Pin (VFB ~500mV) 250 mV

ILIM

Description)

Internal IC Temperature

Soft-Start

tSS V

tEN Fault Enable/SSOK (T1.0)

to Regulation (T0.8) 5.3 ms

OUT

Frequency=600KHz

Note:

2. Specifications guaranteed by design and characterization; not production tested.

8 12 mA

255 300 345 KHz

540 600 660 KHz

0.53 V

0.4 3.2 V

12 15 18 A

+30 °C

OUT

OUT

6.7 ms

FAN2108 — TinyBuck™, 3-24V Input, 8A, High-Efficiency, Integrated Synchronous Buck Regulator

© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN2108 • Rev. 1.0.1 5