Richtek RT7277GSP Schematic [ru]

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®

RT7277

3A, 18V, 700kHz ACOTTM Synchronous Step-Down Converter

General Description

The RT7277 is a synchronous step-downDC/DC converter withAdvanced Constant On-Time (ACOTTM) mode control. It achieves high power density to deliver up to 3A output current from a 4.5V to 18V input supply. The proprietary ACOTTM mode offers an optimal transient response over a wide range of loads and all kinds of ceramic capacitors, which allows the device to adopt very low ESR output capacitors for ensuring performance stabilization. In addition, RT7277 keeps an excellent constant switching frequency under line and load variation and the integrated synchronous power switches with the ACOTTM mode operation provides high efficiency in whole output current load range. Cycle-by-cycle current limit provides an accurate protection by a valley detection of low side MOSFET and external soft-start setting eliminates input current surge during startup. Protection functions also include output under voltage protection, output over voltage protection, and thermal shutdown.

Marking Information

RT7277

RT7277GSP : Product Number

YMDNN : Date Code

GSPYMDNN

 

 

 

Features

zACOTTM Mode Enables Fast Transient Response

z4.5V to 18V Input Voltage Range

z3A Output Current

z60mΩ Internal Low Site N-MOSFET

zAdvanced Constant On-Time Control

zSupport All Ceramic Capacitors

zUp to 95% Efficiency

z700kHz Switching Frequency

zAdjustable Output Voltage from 0.765V to 8V

zAdjustable Soft-Start

zCycle-by-Cycle Current Limit

zInput Under Voltage Lockout

zThermal Shutdown

zRoHS Compliant and Halogen Free

Applications

zIndustrial and Commercial Low Power Systems

zComputer Peripherals

zLCD Monitors and TVs

zGreen Electronics/Appliances

zPoint of Load Regulation for High-Performance DSPs, FPGAs, and ASICs

Simplified Application Circuit

 

RT7277

L1

 

VIN

VIN

SW

 

VOUT

C1

C2

 

C6

C7

 

 

BOOT

C3

R1

Chip Enable

 

 

 

EN

FB

 

 

 

 

 

 

SS

PVCC

VPVCC

R2

 

C5

GND

C4

 

 

 

 

 

Copyright ©2013 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS7277-01 March 2013

www.richtek.com

 

1

RT7277

Ordering Information

RT7277

Package Type

SP : SOP-8 (Exposed Pad-Option 2)

Lead Plating System

G : Green (Halogen Free and Pb Free)

Note :

Richtek products are :

`RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.

`Suitable for use in SnPb or Pb-free soldering processes.

Pin Configurations

(TOP VIEW)

EN

 

8

VIN

FB

2

7

BOOT

PVCC

3

GND

SW

6

SS

4

9

GND

5

SOP-8 (Exposed Pad)

Functional Pin Description

Pin No.

Pin Name

Pin Function

1

EN

Enable Input. A logic-high enables the converter; a logic-low forces the IC into

shutdown mode reducing the supply current to less than 10μA.

 

 

 

 

Feedback Input. It is used to regulate the output of the converter to a set value via

2

FB

an external resistive voltage divider. The feedback threshold voltage is 0.765V

 

 

typically.

3

PVCC

Internal Regulator Output. Connect a 1μF capacitor to GND to stabilize output

voltage.

 

 

 

 

Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from

4

SS

SS to GND to set the soft-start period. A 3.9nF capacitor sets the soft-start period of

 

 

VOUT to 2.6ms.

5, 9

GND

Ground. The Exposed pad should be soldered to a large PCB and connected to

(Exposed Pad)

GND for maximum thermal dissipation.

6

SW

Switch Node. Connect this pin to an external L-C filter.

 

 

 

7

BOOT

Bootstrap Supply for High Side Gate Driver. Connect a 0.1μF or greater ceramic

capacitor from BOOT to SW pins.

 

 

8

VIN

Power Input. The input voltage range is from 4.5V to 18V. Must bypass with a

suitably large ( ≥10μF x 2) ceramic capacitor.

 

 

Copyright ©2013 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS7277-01 March 2013

2

 

RT7277

Function Block Diagram

PVCC

 

 

BOOT

 

Internal

 

 

 

VIN

Regulator

 

 

 

 

 

 

 

PVCC

Over Current

PVCC

 

VIBIAS

VREF

Protection

 

 

 

 

UGATE

 

 

 

 

 

 

Switch

Driver

SW

 

 

Controller

PVCC

Ripple

 

 

 

 

LGATE

 

Gen.

 

 

GND

2µA

+

 

SW

 

SS

 

 

 

-

 

 

 

FB

-

FB

 

 

 

 

 

 

 

Comparator

 

 

On-Time

 

 

EN

 

 

 

 

EN

 

Operation

In normal operation, the high side N-MOSFET is turned on when the FB Comparator sets the Switch Controller, and it is turned off when On-Time Controller resets the Switch Controller. While the high sideN-MOSFET is turned off, the low side N-MOSFET is turned on and waits for the FB Comparator to set the beginning of next cycle.

The FB Comparator sets the Switch Controller by comparing the feedback signal (FB) from output voltage with the internal 0.765V reference. When load transient induces VOUT drop, the FB voltage will be less than its threshold voltage. This means that the high sideN-MOSFET will turn on again immediately after minimum off-time expired. The switching frequency will vary during the transient period thus can provide a very fast transient response. After the load transient finished, the RT7277 will be back to steady state with a constant switching frequency.

Enable

Activate internal regulator once EN input level is higher than the target level. Force IC to enter shutdown mode when the EN input level is lower than 0.4V

Internal Regulator

Provide internal power for logic control and switch gate drivers.

On-Time Controller

Control on-time according to VIN and SW to obtain constant switching frequency.

Copyright ©2013 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS7277-01 March 2013

www.richtek.com

 

3

RT7277

Absolute Maximum Ratings

(Note 1)

 

 

 

 

 

 

 

z Supply Voltage, VIN -----------------------------------------------------------------------------------------------

 

 

 

 

 

−0.3V to 21V

 

z Switch Voltage, SW -----------------------------------------------------------------------------------------------

 

 

 

 

 

−0.8V to (VIN + 0.3V)

<10ns -----------------------------------------------------------------------------------------------------------------

 

 

 

 

 

−5V to 25V

 

z BOOT to SW, PVCC ----------------------------------------------------------------------------------------------

 

 

 

 

 

−0.3V to 6V

 

z Other Pins Voltage -------------------------------------------------------------------------------------------------

 

 

 

 

 

−0.3V to 21V

 

z Power Dissipation, PD @ TA = 25°C

 

 

 

 

 

 

 

 

 

SOP-8 (Exposed Pad) --------------------------------------------------------------------------------------------

 

 

 

 

 

2.041W

 

z Package Thermal Resistance

(Note 2)

 

 

 

 

 

 

 

 

 

SOP-8 (Exposed Pad), θJA ---------------------------------------------------------------------------------------

 

 

 

 

 

49°C/W

 

SOP-8 (Exposed Pad), θJC --------------------------------------------------------------------------------------

 

 

 

 

 

15°C/W

 

z Junction Temperature Range -------------------------------------------------------------------------------------

 

 

 

 

 

150°C

 

 

 

z Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------

 

 

 

 

260°C

 

 

 

z Storage Temperature Range -------------------------------------------------------------------------------------

 

 

 

 

 

−65°C to 150°C

z ESD Susceptibility (Note 3)

 

 

 

 

 

 

 

 

 

 

HBM (Human Body Model) ---------------------------------------------------------------------------------------

 

 

 

 

 

2kV

 

 

 

Recommended Operating Conditions

(Note 4)

 

 

 

 

 

 

z Supply Voltage, VIN -----------------------------------------------------------------------------------------------

 

 

 

 

 

4.5V to 18V

 

z Junction Temperature Range -------------------------------------------------------------------------------------

 

 

 

 

 

−40°C to 125°C

z Ambient Temperature Range -------------------------------------------------------------------------------------

 

 

 

 

 

−40°C to 85°C

 

Electrical Characteristics

 

 

 

 

 

 

 

 

 

(VIN = 12V, TA = 25°C, unless otherwise specified)

 

 

 

 

 

 

 

Parameter

Symbol

 

Test Conditions

Min

Typ

 

Max

Unit

Supply Current

 

 

 

 

 

 

 

 

 

 

Shutdown Current

ISHDN

 

VEN = 0V

 

--

1.5

 

10

 

μA

Quiescent Current

IQ

 

VEN = 3V, VFB = 1V

--

0.7

 

--

 

mA

Logic Threshold

 

 

 

 

 

 

 

 

 

 

EN Voltage

Logic-High

 

 

 

 

2

--

 

18

 

V

 

 

 

 

 

 

 

 

 

 

Logic-Low

 

 

 

 

--

--

 

0.4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VFB Voltage and Discharge Resistance

 

 

 

 

 

 

 

 

 

Feedback Threshold Voltage

VFB

 

4.5V ≤ VIN ≤ 18V

0.757

0.765

 

0.773

 

V

Feedback Input Current

IFB

 

VFB = 0.8V

 

−0.1

0

 

0.1

 

μA

VPVCC Output

 

 

 

 

 

 

 

 

 

 

VPVCC Output Voltage

VPVCC

 

6V ≤ VIN ≤ 18V, 0 < IPVCC < 5mA

4.7

5.1

 

5.5

 

V

Line Regulation

 

 

6V ≤ VIN ≤ 18V, IPVCC = 5mA

--

--

 

20

 

mV

Load Regulation

 

 

0 < IPVCC < 5mA

--

--

 

100

 

mV

 

 

 

 

 

 

 

 

 

 

Output Current

IPVCC

 

VIN = 6V, VPVCC = 4V

--

110

 

--

 

mA

 

 

 

 

 

 

 

 

 

 

 

 

Copyright ©2013 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

 

www.richtek.com

 

 

 

 

 

DS7277-01 March

2013

4

 

 

 

 

 

 

 

 

 

 

 

RT7277

Parameter

Symbol

Test Conditions

Min

Typ

Max

Unit

RDS(ON)

 

 

 

 

 

 

 

Switch On

High Side

RDS(ON)_H

 

--

90

--

Resistance

Low Side

RDS(ON)_L

 

--

60

--

 

 

 

 

 

 

 

 

 

 

Current Limit

 

 

 

 

 

 

 

Current Limit

 

ILIM

 

3.5

4.1

5.7

A

Thermal Shutdown

 

 

 

 

 

 

Thermal Shutdown Threshold

TSD

 

--

150

--

°C

Thermal Shutdown Hysteresis

TSD

 

--

20

--

°C

On-Time Timer Control

 

 

 

 

 

 

On-Time

 

tON

VIN = 12V, VOUT = 1.05V

--

145

--

ns

 

 

 

 

 

 

 

Minimum On-Time

tON(MIN)

 

--

60

--

ns

Minimum Off-Time

tOFF(MIN)

 

--

230

--

ns

Soft-Start

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SS Charge Current

 

VSS = 0V

1.4

2

2.6

μA

SS Discharge Current

 

VSS = 0.5V

0.05

0.1

--

mA

UVLO

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

UVLO Threshold

 

 

VIN Rising to Wake up VPVCC

3.55

3.85

4.15

V

Hysteresis

 

 

 

--

0.3

--

 

 

 

 

 

 

 

 

 

 

 

 

Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability.

Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is measured at the exposed pad of the package. The PCB copper area of exposed pad is 70mm2.

Note 3. Devices are ESD sensitive. Handling precaution is recommended.

Note 4. The device is not guaranteed to function outside its operating conditions.

Copyright ©2013 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS7277-01 March 2013

www.richtek.com

 

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