Richtek RT7266ZSP Schematic [ru]

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

RT7266

General Description

The RT7266 is an adaptive on-time ACOTTM mode synchronous buck converter. The a daptive on-ti me ACOT

mode control provides a very fast tra nsient response with few external components. The low impedance internal MOSFET can support high ef ficiency operation with wide input voltage range from 4.5V to 18V . The proprietary circuit of the RT7266 enables to support all ceramic ca pacitors. The output voltage ca n be adjustable between

0.8V and 8V. The soft-start is adjustable by an external ca p acitor.

Ordering Information

RT7266

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

Lead Plating System Z : ECO (Ecological Element with Halogen Free and Pb free)

Note : Richtek products are :

 RoHS compliant and compatible with the current require-

ments of IPC/JEDEC J-STD-020.

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

Features

z ACOT

z 4.5V to 18V Input Voltage Range

z 3A Output Current

z 60m

z Adaptive On-Time Control

z Fast T ran sient Respon se

z Support All Ceramic Capa citors

z Up to 95% Efficiency

z 700kHz Switching Frequency

z Adjustable Output Voltage from 0.8V to 8V

z Adjustable Soft-Start

z Cycle-by-Cycle Current Limit

z Input Under Voltage Lockout

z Thermal Shutdown Protection

z RoHS Compliant and Halogen Free

Mode Enable s Fa st T ra n sient Respon se

ΩΩ

Ω Internal Low Site N-MOSFET

ΩΩ

Applications

z Industrial and Commerci al Low Power Systems z Computer Peripherals z LCD Monitors a nd TVs z Green Electronics/Appliance s z Point of Load Regulation for High-Performance DSPs,

FPGAs, and ASICs

Marking Information

RT7266ZSP : Product Number

RT7266 ZSPYMDNN

YMDNN : Date Code

Pin Configurations

(TOP VIEW)

PVCC

GND

3 4

VIN

BOOT

GND

SOP-8 (Exposed Pad)

DS7266-02 September 2012 www.richtek.com

RT7266

Typical Application Circuit

Chip Enable

(V) R1 (kΩ) R2 (kΩ) C3 (pF) L1 (μH) C7 (μF)

OUT

1 6.81 22.1 -- 1.4 22 to 68

1.05 8.25 22.1 -- 1.4 22 to 68

1.2 12.7 22.1 -- 1.4 22 to 68

1.8 30.1 22.1 5 to 22 2 22 to 68

C1 10µF x 2

5, 9 (Exposed Pad)

3.9nF

0.1µF

Table 1. Suggested Component Values

VIN

EN GND SS

RT7266

BOOT

PVCC

0.1µF

C4 1µF

1.4µH

PVCC

8.25k

22.1k

C7 22µF x 2

7 2 3

OUT

1.05V/3A

2.5 49.9 22.1 5 to 22 2 22 to 68

3.3 73.2 22.1 5 to 22 2 22 to 68 5 124 22.1 5 to 22 3.3 22 to 68 7 180 22.1 5 to 22 3.3 22 to 68

Functional Pin Description

Pin No. Pin Name Pin Function

Enable Input. A logic-high enables the converter; a logic-low forces the RT7266

1 EN

2 FB

3 PVCC

4 SS

5, 9 (Exposed pad) GND

6 SW Switch Node. Connect this pin to an external L-C filter. 7 BOOT

8 VIN

into shutdown mode reducing the supply current to less than 10μA. Attach this pin to VIN with a 100kΩ pull up resistor for automatic start-up.

Feedback Input. It is used to regulate the output of the converter to a set value via an external resistive voltage divider. The feedback reference voltage is

0.765V typically. 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 SS to GND to set the soft-start period. A 3.9nF capacitor sets the soft-start p eriod to 1.5ms.

Ground. The Exposed pad should be soldered to a large PCB and connected to GND for maximum thermal dissipation.

Bootstrap for High Side Gate Driver. Connect a 0.1μF or greater ceramic capacitor fr om BOOT to SW pins.

Supply Input. The input voltage range is from 4.5V to 18V. Mus t bypass with a suitable large ( ≥10μF x 2) ceramic capacitor.

DS7266-02 September 2012www.richtek.com

Function Block Diagram

VIN

RT7266

PVCC

Reg

Soft-Start

On-Time

Control

REF

Driver

Comparator

UGATE

LGATE

BOOT

GND

DS7266-02 September 2012 www.richtek.com

RT7266

Absolute Maximum Ratings (Note 1)

z Supply V oltage, VIN ----------------------------------------------------------------------------------------------- −0.3V to 20V z Switch Voltage, SW ----------------------------------------------------------------------------------------------- −0.8V to (V

< 10ns----------------------------------------------------------------------------------------------------------------- −5V to 25V

z BOOT to SW -------------------------------------------------------------------------------------------------------- −0.3V to 6V z All Other Pins ------------------------------------------------------------------------------------------------------- −0.3V to 6V z Power Dissipation, P

@ TA = 25°C

SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------------- 1.333W

z Package Thermal Re sistance (Note 2)

SOP-8 (Exposed Pad), θJA--------------------------------------------------------------------------------------- 75°C/W SOP-8 (Exposed Pad), θJC-------------------------------------------------------------------------------------- 15°C/W

z Junction T emperature Range------------------------------------------------------------------------------------- 150°C z Lead Temperature (Soldering, 10 sec.)------------------------------------------------------------------------ 260°C z Storage T emperature Range ------------------------------------------------------------------------------------- − 65°C to 150°C

+ 0.3V)

Recommended Operating Conditions

z Supply V oltage, VIN ----------------------------------------------------------------------------------------------- 4.5V to 18V z Junction T emperature Range------------------------------------------------------------------------------------- −40°C to 125°C z Ambient T emperature Range------------------------------------------------------------------------------------- −40°C to 85°C

(Note 3)

Electrical Characteristics

(VIN = 12V, T

Supply Current

Shutdown Current I Quiescent Current IQ V

Logic Threshold

EN Voltage

Voltage and Discharge Resistance

REF

Feedback Reference Voltage V Feedback Input Current IFB V

PVCC

Line Regulation 6V ≤ V Load Regulati on 0 < I Output Current I

DS(ON)

Switch On Resistan ce

Current Limit Current limit I

= 25°C, unless otherwise specified)

Parameter Symbol Test Conditions Min Typ Max Unit

SHDN

= 0V -- 1 10 μA

= 3V, VFB = 1V -- 0.7 -- mA

Logic-High 2 -- 5.5 Logic-Low -- -- 0.4

4.5V ≤ V

REF

= 0.8V −0.1 0 0.1 μA

≤ 18V 0.753 0.765 0.777 V

Output Output Voltage V

6V ≤ V

PVCC

= 6V, V

≤ 18V, 0 < I

≤ 18V, I

PVCC

< 5mA 4.7 5.1 5.5 V

PVCC

= 5mA -- -- 20 mV

< 5mA -- -- 60 mV

= 4V -- 110 - - m A

PVCC

High Side R Low Side R

DS(ON)_H DS(ON)_L

3.5 4.1 5.7 A

LIM

-- 90 --

-- 60 --

mΩ

DS7266-02 September 2012www.richtek.com

RT7266

Parameter Symbol Test Conditions Min Typ Max Unit

The rmal Shutdown

Thermal Shutdown Threshold TSD -- 150 -Thermal Shutdown

Hysteresis

ΔT

-- 20 --

On-Ti me Timer Cont rol

On-Time tON V Mi n imum On-Time t Mi n imum Off- T ime t

ON(MIN) OFF(MIN)

-- 60 -- ns

= 12V, V

= 1.05V -- 14 5 -- ns

OUT

-- 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 -- m A

UVLO

UVLO Thr eshold VIN Risi ng to Wake up V

3.55 3.85 4.15

PVCC

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. θ

Note 3. The device is not guaranteed to function outside its operating conditions.

is measured at T

measured at the exposed pad of the package.

= 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is

°C

DS7266-02 September 2012 www.richtek.com

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Richtek RT7266ZSP Schematic [ru]

Specifications and Main Features

Frequently Asked Questions

User Manual