Richtek RT8055GQW, RT8055GSP, RT8055ZQW Schematic [ru]

®

RT8055

3A, 2MHz, Synchronous Step-Down Converter

General Description

The RT8055 is a high efficiency synchronous, step-down DC/DC converter. Its input voltage range is from 2.6V to 5.5V and provides an adjustable regulated output voltage from 0.8V to 5V while delivering up to 3A of output current.

The internal synchronous low on-resistance power switches increase efficiency and eliminate the need for an external Schottky diode. The switching frequency is set by an external resistor. The 100% duty cycle provides low dropout operation extending battery life in portable systems. Current mode operation with external compensation allows the transient response to be optimized over a wide range of loads and output capacitors.

The RT8055 is operated in forced continuous PWM Mode which minimizes ripple voltage and reduces the noise and RF interference.

The RT8055 is available in the WDFN-10L 3x3 and SOP-8 (Exposed Pad) packages.

Features

zHigh Efficiency : Up to 95%

zLow RDS(ON) Internal Switches : 100mΩ

zProgrammable Frequency : 300kHz to 2MHz

zNo Schottky Diode Required

z0.8V Reference Voltage Allows for Low Output Voltage

zForced Continuous Mode Operation

z100% Duty Cycle Operation

zInput Over Voltage Protection

zRoHS Compliant and Halogen Free

Applications

zPortable Instruments

zBattery-Powered Equipment

zNotebook Computers

zDistributed Power Systems

zIP Phones

zDigital Cameras

z3G/3.5GData Card

Ordering Information

RT8055

Package Type

QW : WDFN-10L 3x3 (W-Type)

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

Lead Plating System

G : Green (Halogen Free and Pb Free) 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.

Pin Configurations

(TOP VIEW)

	SHDN/RT 1			10	COMP
	GND 2		GND	9	FB
	LX 3			8	VDD
	LX 4			7	PVDD
	PGND 5		11 6		PVDD
	WDFN-10L 3x3
	SHDN/RT			8	COMP
	GND	2	GND	7	FB
	LX	3		6	VDD
			9
	PGND	4		5	PVDD

SOP-8 (Exposed Pad)

Copyright ©2012 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8055-05 November 2012	www.richtek.com
	1

RT8055

Marking Information

RT8055GQW			RT8055GSP
		JN= : Product Code			RT8055GSP : Product Number
				RT8055
	JN=YM	YMDNN : Date Code			YMDNN : Date Code
				GSPYMDNN
	DNN

RT8055ZQW

JN : Product Code

YMDNN : Date Code

JN YM

DNN

Typical Application Circuit

VIN
5V							CIN
							22µF

C1

0.1µF

ROSC

180k

		L1
PVDD	LX	2µH		VOUT
				3.3V/3A
RT8055
			R1	COUT
VDD				22µF x 2
			75k
	FB		R2
SHDN/RT	COMP		24k
GND		RCOMP
		30k
PGND		CCOMP
		470pF

Table 1. Recommended Component Selection

VOUT	R1 (kΩ)	R2 (kΩ)	RCOMP (kΩ)	CCOMP (nF)	L1 (μH)	COUT (μF)
3.3	75	24	30	0.47	2.2	22 x 2
2.5	51	24	27	0.47	2.2	22 x 2
1.8	30	24	22	0.47	2.2	22 x 2
1.5	21	24	18	0.47	2.2	22 x 2
1.2	12	24	15	0.47	1.0	22 x 2
1.0	6	24	13	0.47	1.0	22 x 2

Copyright ©2012 Richtek Technology Corporation. All rights reserved.	is a registered trademark of Richtek Technology Corporation.
www.richtek.com	DS8055-05 November 2012

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RT8055

Functional Pin Description

Pin No.			Pin Name	Pin Function
WDFN-10L 3x3		SOP-8
				Shutdown Control or Frequency Setting Input. Connect a
1		1	SHDN/RT	resistor to ground from this pin sets the switching frequency.
				Force this pin to VDD or GND causes the device to be shut down.
				Signal Ground. All small-signal components and compensation
2,		2,		components should be connected to this ground, which in turn
			GND	connects to PGND at one point. The exposed pad must be
11 (Exposed Pad)	9 (Exposed Pad)
				soldered to a large PCB and connected to GND for maximum
				power dissipation.
3, 4		3	LX	Internal Power MOSFET Switches Output. Connect this pin to
				the inductor.
5		4	PGND	Power Ground. Connect this pin close to the negative terminal of
				CIN and COUT.
6, 7		5	PVDD	Power Supply Input. Decouple this pin to PGND with a capacitor.
8		6	VDD	Signal Supply Input. Decouple this pin to GND with a capacitor.
				Generally, VDD is equal to PVDD.
9		7	FB	Feedback Pin. This pin receives the feedback voltage from a
				resistive divider connected across the output.
				Error Amplifier Compensation Point. The current comparator
10		8	COMP	threshold increases with this control voltage. Connect external
				compensation elements to this pin to stabilize the control loop.

Function Block Diagram

SHDN/RT

PVDD

SD

ISEN

OSC

Slope

COMP

Comp.

0.8V

OC

EA

Output

FB

Clamp

Limit

LX

Internal -

Driver

Soft Star

Control

0.7V

Logic

NISEN

PGND

OTP

POR

0.4V

N-MOSFET ILIM

GND

VDD

VREF

Copyright ©2012 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8055-05 November 2012

www.richtek.com

3

RT8055

Absolute Maximum Ratings			(Note 1)
z Supply Input Voltage, VDD, PVDD		----------------------------------------------------------------------------					−0.3V to 6.5V
z LX Pin Switch Voltage --------------------------------------------------------------------------------------------							−0.3V to (PVDD + 0.3V)
<10ns ----------------------------------------------------------------------------------------------------------------							−5V to 8.5V
z Other I/O Pin Voltages -------------------------------------------------------------------------------------------							−0.3V to 6.5V
z LX Pin Switch Current --------------------------------------------------------------------------------------------							4A
z Power Dissipation, PD @ TA = 25°C
WDFN-10L 3x3 -----------------------------------------------------------------------------------------------------							1.667W
SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------------							1.333W
z Package Thermal Resistance (Note 2)
WDFN-10L 3x3, θJA -----------------------------------------------------------------------------------------------							60°C/W
WDFN-10L 3x3, θJC -----------------------------------------------------------------------------------------------							7.8°C/W
SOP-8 (Exposed Pad), θJA -------------------------------------------------------------------------------------							75°C/W
SOP-8 (Exposed Pad), θJC -------------------------------------------------------------------------------------							15°C/W
z Junction Temperature ---------------------------------------------------------------------------------------------							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 Input Voltage ----------------------------------------------------------------------------------------------							2.6V to 5.5V
z Junction Temperature Range ------------------------------------------------------------------------------------							−40°C to 125°C
z Ambient Temperature Range ------------------------------------------------------------------------------------							−40°C to 85°C
Electrical Characteristics
(VDD = 3.3V, TA = 25°C, unless otherwise specified)
Parameter		Symbol		Test Conditions		Min	Typ	Max		Unit
Input Voltage Range		VDD				2.6	--	5.5		V
Feedback Reference Voltage		VREF				0.784	0.8	0.816		V
Feedback Leakage Current		IFB		VFB = 3.3V		--	--	0.1		μA
DC Bias Current				Active , VFB = 0.7V, Not Switching		--	500	--		μA
				Shutdown		--	--	1		μA
Output Voltage Line Regulation		VLINE		VIN = 2.6V to 5.5V		--	0.1	--		%/V
Output Voltage Load Regulation		VLOAD		VIN = 5V, VOUT = 3.3V,		--	0.4	--		%
				IOUT = 0A to 3A
Error Amplifier		gm				--	400	--		μA/V
Transconductance
Current Sense Transresistance		RS				--	0.4	--		Ω
RT Leakage Current				SHDN/RT = VIN = 5.5V		--	--	1		μA
Copyright ©2012 Richtek Technology Corporation. All rights reserved.					is a registered trademark of Richtek Technology Corporation.
www.richtek.com						DS8055-05		November 2012

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RT8055

Parameter	Symbol	Test Conditions	Min	Typ	Max	Unit
		ROSC = 180kΩ	1.44	1.8	2.16
Switching Frequency						MHz
		Adjustable Switching Frequency	0.3	--	2
		Range
Switch On Resistance, High	RDS(ON)_P	ISW = 0.3A	--	100	160	mΩ
Switch On Resistance, Low	RDS(ON)_N	ISW = 0.3A	--	100	170	mΩ
Peak Current Limit	ILIM		3.5	--	--	A
Under Voltage Lockout		VDD Rising @Full Temperature	2.33	2.4	2.57	V
Threshold (Note 5)		VDD Falling @Full Temperature	1.98	2.2	2.37
Shutdown Threshold	VSHDN	VSHDN Rising	--	VIN − 0.85	VIN − 0.4	V

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. Devices are ESD sensitive. Handling precaution is recommended.

Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. Guaranteed by design.

Copyright ©2012 Richtek Technology Corporation. All rights reserved.	is a registered trademark of Richtek Technology Corporation.
DS8055-05 November 2012	www.richtek.com
	5