F72814 Datasheet

Synchronous Buck PWM DC-DC Controller

Release Date: July, 2007

Version: V0.23P

F72814

V0.23P

F72814 Datasheet Revision History

Version Date Page History

0.20P

F72814

4

8

11

Add dead time measurement loading

Add typical characteristic diagram

Update company address

Please note that all data and specifications are subject to change without notice. All the trade marks of products and companies mentioned in this data sheet belong to their respective owners.

LIFE SUPPORT APPLICATIONS

These products are not designed for use in life support appliances, devices, or systems where malfunction of these products can reasonably be expected to result in personal injury. Customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify Fintek for any damages resulting from such improper use or sales.

V0.23P

Table of Content

F72814

5. Electrical Characteristic ..................................................................................................................2

7.2 Power On Reset...........................................................................................................................5

7.3 Soft-Start .....................................................................................................................................6

7.4 Over-current Protection ..............................................................................................................6

7.6 Shutdown ....................................................................................................................................7

10. Package Dimensions (8-SOP/150 mil) .........................................................................................11

V0.23P

F72814

1. General Description

The F72814 is a high-efficiency synchronous buck PWM controller that generates logic-supply voltages in PC based systems. This high-performance , single output device includes internal soft-start, frequency-compensation networks, power good signal with delay, and integrates all of the control, output adjustment, monitoring and protection functions into a single package. This device operates at a fixed frequency, 300K Hz and provides an optimum compromise between efficiency, external component size, and cost. Adjustable over-current protection (OCP) monitors the voltage drop across the RDS (ON) of the lower MOSFET for synchronous buck PWM DC-DC controller. The over-current function cycles the soft-start in 4-times hiccup mode to provide fault protection, and in a routine hiccup mode for under-voltage protection.

2. Feature List

Æ

Provides one synchronous rectified buck DC-DC PWM controller

̈

Fast transient response (high bandwidth error amplifier; full 0~ 80 % duty cycle)

̈

Fixed operation frequency : 300KHz

̈

Single loop voltage-mode control

̈

Few external components

̈

Output range adjustable down to 0.8V

Æ

Operates under 5V to 12V input

Æ

Drives all low cost N-channel MOSFETs

Æ

Uses MOSFET R

DS(ON)

as over current monitor, and no current sense resistor is required

Æ

0.8V internal reference voltage

̈

±2% accuracy over line, load and temperature

Æ

Internal soft-start (typically 3 ms)

Æ

Under voltage fault monitoring and protection

Æ

Over voltage protection

Æ

Adaptive Non-Overlapping Gate Driver

Æ

8-SOP package (150 mil)

F72814 V0.23P

F72814

3. Pin Configuration

BOOT

UGATE

GND

LGATE

3

4

1

2

F72814

8

7

6

5

PHASE

OCSET

FB

VCC

4. Pin Description

2

3

4

5

6

Pin No

1

Pin Name

BOOT

UGATE

GND

LGATE

VCC

FB

7

8

OCSET/SD

PHASE

Description

Bootstrap supply pin for the upper gate driver. Connect the bootstrap capacitor between

BOOT pin and the PHASE pin. The bootstrap capacitor provides the charge to turn on the upper MOSFET.

Higher gate drive output. Connect this pin to gate of the high side MOSFET

Power ground pin for the chip

Lower gate drive output. Connect this pin to gate of the low side MOSFET

IC supply voltage. This voltage is monitored for power-on-reset purpose.

Inverting input of the error amplifier used to compensate the feedback loop of the PWM controller.

This is multi-function pin. Connecting a resistor ROCSET from this pin to PHASE, and an internal 40uA current source from VCC. OCSET voltage can sense loading status when low side MOSFET turn on. When OCSET voltage is under 0.1V, shut down (SD) function will be enabled.

Connect this pin to the source of the upper MOSFET and the drain of the lower MOSFET.

5. Electrical Characteristic

Absolute Maximum Ratings

IC supply voltage

PHASE to GND

BOOT to PHASE

VCC

VPHASE – GND

VBOOT - VPHASE

15

15

15

V

V

V

F72814 V0.23P

BOOT to GND

PWM controller outputs

PWM controller outputs

Feedback voltages

ESD classification

Maximum junction temperature (plastic package)

Maximum storage temperature

Maximum lead temperature (soldering 10s)

VBOOT - GND

UGATE

LGATE

FB

HBM

T j

T

STO

VCC + 15

(VPHASE - 0.3) to (VBOOT + 0.3)

(GND - 0.3) to (VCC + 0.3)

(GND - 0.3) ~ 7

2

-65 ~ 150

F72814

V

V

V

V kV

°C

Note:

If ICs are stressed beyond the limits listed in the “absolute maximum ratings”, they may be permanently destroyed. These are stress ratings only and functional operations of the device at these or any other condition beyond those indicated under “recommended operating conditions” are not implied.

Exposure to absolute maximum rated conditions for extended periods may affect device reliability.

Recommended Operating Conditions

Supply Voltage

Ambient Temperature

Junction Temperature

VCC 5

± 5%,12 ± 10%

0 ~ 70

0 ~ 125

V

°C

°C

Package thermal information

Thermal resistance junction-ambient Rth_ja 160 °C/W

DC and AC electrical characteristics

(VCC = 12V, TA = 25 )

PARAMETER SYMBOL TEST CONDITIONS

VCC SUPPLY CURRENT/Regulated Voltage

Nominal supply current 5VCC I

CC

POWER-ON RESET

Rising VCC threshold

UGATE, LGATE and DRIVE2 open

Falling VCC threshold

OSCILLATOR AND Protection

Free running frequency

Ramp Amplitude

FB Under Voltage Trip

OCSET Current Source

Soft-start interval

F

OSC

V

OSC

FB Falling

I

OCSET

T

SS

MIN.

TYP. MAX. UNIT

6

4.1

3.6

15

4.4

3.75 mA

V

V

250 300 350 kHz

1.5

V

P-P

0.48 0.5 0.52 V

35 40 45 uA

1 3 6 ms

F72814 V0.23P

PARAMETER

Dead time

SYMBOL TEST CONDITIONS

T

DT

2V to 2V, Loading =2A

REFERENCE VOLTAGE

Reference voltage

PWM CONTROLLER GATE DRIVERS

Upper Drive Source

Upper Drive Sink

R

UGATE

R

UGATE

Lower Drive Source

V

REF

R

LGATE

R

LGATE

Lower Drive Sink

Error Amplifier

E/A Transconductance

DC Gain

: Design Guarantee

VCC=5V, T= 25

VDS = 1V, VGS = 12V,

VDS = 1V, VGS = 12V

VDS = 1V, VGS = 12V

VDS = 1V, VGS = 12V gm

A0

6. Block Diagram

FB

F72814

MIN.

TYP. MAX. UNIT

10 100

4

3

5

4

10

8

8

5 ns

0.784

0.8 0.816 V

1.67

85

*

dB

VDDA

Reference

Voltage

0.8V

GM

Bias & Regulator

(VDD & V3VAA)

0.6V

UVP

UV

Comp

Power On

Reset

Control

Logic

VDD

OC

Comp

0.4V

V3VAA

40uA

SD

Comp

0.15V

PH_M

Comp

1.5V

OCSET

BOOT

UGATE

PHASE

VDDA

LGATE

300KHz Tri-OSC

GND

Figure 1

: Block Diagram

F72814 V0.23P

F72814

7. Function Description

The F72814 is a single PWM DC-DC converter controller for application which requires high current such as motherboard, graphic card etc. The F72814 uses voltage mode PWM controller with fast transient response (driving two external N-channel

MOSFETs in a synchronous rectified buck converter topology) and integrates some functions such as soft-start, over current and short circuit protections etc. Over current protection is achieved by monitoring the PHASE negative voltage when heavy loading without the need of a current sensing resistor and short circuit condition is detected through FB pin. If over current condition occurs, the F72814 will initiate the soft start cycle. After two cycles and the fault condition persist, the controller will go into shut down status. In shut down status, both gate drive signals will be low. To restart the controller, either recycling VCC supply or momentarily pulling the OCSET pin below 0.15V. If under voltage condition occurs, it will keep hiccup mode in this event.

7.1 Bootstrap Operation

In the single power supply system, UGATE is powered by an external bootstrap circuit as Figure 3. The Boot capacitor, C

BOOT

is charged and generated a floating reference voltage at PHASE pin. Typically, a 0.1uF C

BOOT

is enough for the most of applications.

The C

BOOT

capacitor is refreshed and charged to a voltage of “VCC – Diode Drop” while low side power MOS turns on.

5V to 12V

3.3V/5V/12V

BOOT

VCC

C

BOOT

UGATE

Q1

PHASE

VOUT

LGATE

Q2

Fig 2. Power Supply Operation.

7.2 Power On Reset

The F72814S Power-on-reset monitors VCC supply voltage and input voltage at OCSET pin. POR level is 4.1V with 0.5V hysteresis at VCC voltage and 0.15V at OCSET voltage, The POR function initiates soft-start operation and resets control logic after the supply voltages exceeds its POR threshold voltage.

F72814 V0.23P

F72814

7.3 Soft-Start

When the POR function initiates the digital soft-start sequence, PWM error amplifier reference inputs are forced to track a voltage level proportional to the soft-start voltage. As the soft-start voltage slews up, the PWM comparator regulates the output relative to the tracked soft-start voltage, and slowly charges the output capacitor(s). In the digital soft-start sequence initiated by the POR function, the soft start function is used to prevent surge current from power supply input during power on. The soft start duration is 3mS in typical case.

VCC = 12V

12V

6V VCC = 5V

VOUT

0V

3mS

Figure 3 : Soft start duration

TIME

7.4 Over-current Protection

To sense the low-side MOSFET’s RDS (ON) to set over-current trip point. Connecting a resistor (ROCSET) from this pin to PHASE to set the over-current trip point, ROCSET, an internal 40 A current source, and the lower MOSFET on resistance, RDS (ON), sets the converter over-current trip point (IOCSET) according to the following equation:

7.5 Under-voltage Protection

If the FB voltage drops under 0.5V, a fault signal is generated. When under voltage condition occurs, it will keep hiccup mode in this event.

F72814 V0.23P

F72814

3V

1.5V

VOUT

0V t0 tss 2tss 3tss 4tss TIME

Figure 4 : Under voltage event occur

But UV_FB has some differences from OC, it always trigger VIN power sensing after 4 times hiccup.

7.6 Shutdown

It can shut down the F72814 PWM controller to pull low the OCSET pin under 0.15V.

7.7 VIN Sense

The F72814 Vin power is sensed by OCSET voltage at first soft start event, when soft start event occurs. UGATE pulse will be enabled, and the F72814 detects the first ten UGATE high pulse. If there are four PH_M pulse during the ten pulse period, it means

Vin ready, If Vin is ready, VOUT will be ramped up in next soft start event. Otherwise, we will check Vin voltage at the next soft start event.

VCC

5V

PWOK

VOUT

0V

UGATE

1 2 3 4 5 6 7

TIME (ms

Figure 5 :

F72814 V0.23P

8. Typical Characteristic

F72814

V

CC

=12V, V

IN

=5V, V

OUT

=2.5V V

CC

=5V, V

IN

=5V, V

OUT

=2.5V

0.806

0.802

0.798

0.794

0.79

0.786

-10

Reference Voltage V.S. Temperature

5 20 35 50

Temperature ( )

65 80

POR V.S. Temperature

4.6

Rising

4.2

95 110

350

330

310

290

270

250

-10 5

Frequency V.S. Temperature

20 35 50 65

Temperature ( )

80 95 110

3.8

Falling

3.4

-10 5 20 35 50 65 80 95 110

F72814 V0.23P

F72814

Dead Time (Rising) Dead Time (Falling)

UGATE

UGATE

LGATE

UGATE

Time 20.0ns/Div. Time 20.0ns/Div.

V

CC

=12V, V

IN

=5V, I

OUT

=2.5A

Under Voltage Protection

UGATE

LGATE

FB

FB

FB > 0.5V FB < 0.5V

F72814 V0.23P

Transient Response Time

Rising

UGATE, 20.0V/Div.

V

OUT

, 100mV/Div.

IOUT, 5.0A/Div

UGATE, 20.0V/Div.

V

OUT

, 100mV/Div.

IOUT, 5.0A/Div

V

CC

=5V V

IN

=5V I

OUT

=0-15A

Falling

V

CC

=5V V

IN

=5V I

OUT

=15-0A

9. Ordering Information

Part Number

F72814SG

Package Type Production Flow

8-SOP (Green Package) Commercial, 0

°C to +70°C

F72814

F72814 V0.23P

10. Package Dimensions (8-SOP/150 mil)

8

5 c

F72814

E

H

E

1

4

D

A

Y

SEATING PLANE e b

A1

A

A1 b c

E

D e

H

E

Y

L

θ

Control demensions are in milmeters .

SYMBOL

DIMENSION IN MM

MIN.

MAX.

1.35

0.10

0.33

0.19

1.75

0.25

0.51

0.25

3.80

4.80

1.27 BSC

4.00

5.00

5.80

6.20

0.10

0.40

0

1.27

10

DIMENSION IN INCH

MIN.

MAX.

0.053

0.069

0.010

0.004

0.013

0.020

0.008

0.150

0.188

0.050 BSC

0.196

0.228

0.010

0.157

0.244

0.004

0.016

0

0.050

10

L

0.25

O

GAUGE PLANE

Feature Integration Technology Inc.

Headquarters Taipei Office

3F-7, No 36, Tai Yuan St., Bldg. K4, 7F, No.700, Chung Cheng Rd.,

Chupei City, Hsinchu, Taiwan 302, R.O.C. Chungho City, Taipei, Taiwan 235, R.O.C.

TEL : 886-3-5600168 TEL : 866-2-8227-8027

FAX : 886-3-5600166 FAX : 866-2-8227-8037 www: http://www.fintek.com.tw

Please note that all datasheet and specifications are subject to change without notice. All the trade marks of products and companies mentioned in this datasheet belong to their respective

owner

F72814 V0.23P

F72814S

11. Application Circuit

VCC1P8V

Q1

MOSFET_EN_GDS

L2 3.3u

C5

1000u

C6

1000u

C7

1000u

C8 Q2

MOSFET_EN_GDS

1u

VIN(5V/12V)

L1

1u

VCC(5V/12V)

C1

1u

R2

R4

C2

470u

C3

470u

2.2

2.2

D1

DIODE

C4 0.1u

U1

1

2

3

4

BOOT

UGATE

GND

LGATE

F72814SG

PHASE

OCSET

FB

VCC

8

7

6

5

R5 2.5k

R6 200 C10 0.1u

FB

R3

20k

R1

2.2

C9

1u

R7

2k

12

F72814S

13