Richtek RT7266ZSP Schematic [ru]

®

RT7266

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

Converter

General Description

The RT7266 is an adaptive on-time ACOTTM mode synchronous buck converter. The adaptive on-timeACOTTM mode control provides a very fast transient response with few external components. The low impedance internal MOSFET can support high efficiency operation with wide input voltage range from 4.5V to 18V . The proprietary circuit of the RT7266 enables to support all ceramic capacitors. The output voltage can be adjustable between 0.8V and 8V. The soft-start is adjustable by an external capacitor.

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 requirements of IPC/JEDEC J-STD-020.

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

Features

zACOTTM Mode Enables Fast Transient Response

z4.5V to 18V Input Voltage Range

z3A Output Current

z60mΩ Internal Low Site N-MOSFET

zAdaptive On-Time Control

zFast Transient Response

zSupport All Ceramic Capacitors

zUp to 95% Efficiency

z700kHz Switching Frequency

zAdjustable Output Voltage from 0.8V to 8V

zAdjustable Soft-Start

zCycle-by-Cycle Current Limit

zInput Under Voltage Lockout

zThermal Shutdown Protection

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

Marking Information		Pin Configurations
RT7266	RT7266ZSP : Product Number		(TOP VIEW)
	YMDNN : Date Code
ZSPYMDNN
		EN		8	VIN
		FB	2	7	BOOT
		PVCC	GND		SW
			3	6
		SS	9		GND
			4	5

SOP-8 (Exposed Pad)

Copyright ©2012 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS7266-02 September 2012	www.richtek.com
	1

RT7266

Typical Application Circuit

L1

8

RT7266

6

1.4µH

VOUT

VIN

VIN

SW

1.05V/3A

C1

C2

C6

C7

10µF x 2

0.1µF

7

0.1µF

C3

R1

22µF x 2

8.25k

Chip

Enable

1

EN

BOOT

2

5, 9 (Exposed Pad)

GND

FB

3

R2

4

SS

PVCC

VPVCC

22.1k

C5

C4

3.9nF

1µF

Table 1. Suggested Component Values

VOUT (V)	R1 (kΩ)	R2 (kΩ)	C3 (pF)	L1 (μH)	C7 (μF)
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
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	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
2	FB	via an external resistive voltage divider. The feedback reference 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
4	SS	from SS to GND to set the soft-start period. A 3.9nF capacitor sets the soft-start
		period to 1.5ms.
5, 9 (Exposed pad)	GND	Ground. The Exposed pad should be soldered to a large PCB and connected to
		GND for maximum thermal dissipation.
6	SW	Switch Node. Connect this pin to an external L-C filter.
7	BOOT	Bootstrap for High Side Gate Driver. Connect a 0.1μF or		greater ceramic
		capacitor from BOOT to SW pins.
8	VIN	Supply Input. The input voltage range is from 4.5V to 18V. Must bypass with a
		suitable large ( ≥10μF x 2) ceramic capacitor.
Copyright ©2012 Richtek Technology Corporation. All rights reserved.			is a registered trademark of Richtek Technology Corporation.
www.richtek.com			DS7266-02	September 2012
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RT7266

Function Block Diagram

VIN
PVCC	Reg						BOOT
						UGATE
	OC	Control			Driver		SW
						LGATE	GND
SS	Soft-Start
FB	On-Time	+				EN	EN
			-	Comparator
			VREF

Copyright ©2012 Richtek Technology Corporation. All rights reserved.	is a registered trademark of Richtek Technology Corporation.
DS7266-02 September 2012	www.richtek.com

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RT7266

Absolute Maximum Ratings				(Note 1)
z Supply Voltage, VIN -----------------------------------------------------------------------------------------------								−0.3V to 20V
z Switch Voltage, SW -----------------------------------------------------------------------------------------------								−0.8V to (VIN + 0.3V)
< 10ns-----------------------------------------------------------------------------------------------------------------								−5V to 25V
z BOOT to SW --------------------------------------------------------------------------------------------------------								−0.3V to 6V
z All Other Pins -------------------------------------------------------------------------------------------------------								−0.3V to 6V
z Power Dissipation, PD @ TA = 25°C
SOP-8 (Exposed Pad) --------------------------------------------------------------------------------------------								1.333W
z Package Thermal Resistance			(Note 2)
SOP-8 (Exposed Pad), θJA ---------------------------------------------------------------------------------------								75°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
Recommended Operating Conditions						(Note 3)
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	10		μA
Quiescent Current			IQ		VEN = 3V, VFB = 1V		--	0.7	--		mA
Logic Threshold
EN Voltage		Logic-High					2	--	5.5		V
		Logic-Low					--	--	0.4
VREF Voltage and Discharge Resistance
Feedback Reference Voltage			VREF		4.5V ≤ VIN ≤ 18V		0.753	0.765	0.777		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		--	--	60		mV
Output Current			IPVCC		VIN = 6V, VPVCC = 4V		--	110	--		mA
RDS(ON)
Switch On		High Side	RDS(ON)_H				--	90	--		mΩ
Resistance		Low Side	RDS(ON)_L				--	60	--
Current Limit
Current limit			ILIM				3.5	4.1	5.7		A
Copyright ©2012 Richtek Technology Corporation. All rights reserved.						is a registered trademark of Richtek Technology Corporation.
www.richtek.com							DS7266-02		September 2012
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RT7266

Parameter	Symbol	Test Conditions	Min	Typ	Max	Unit
Thermal Shutdown
Thermal Shutdown Threshold	TSD		--	150	--	°C
Thermal Shutdown	TSD		--	20	--
Hysteresis
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.

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

Copyright ©2012 Richtek Technology Corporation. All rights reserved.	is a registered trademark of Richtek Technology Corporation.
DS7266-02 September 2012	www.richtek.com
	5