Richtek RT8011AGQW, RT8011APQW, RT8011GF, RT8011GQW, RT8011PF Schematic [ru]

RT8011/A

2A, 4MHz, Synchronous Step-Down Regulator

General Description

The RT8011/A 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 2A of output current.

The internal synchronous low on-resistance power switches increase efficiency and eliminate the need for an external Schottky diode. Switching frequency is set by an external resistor or can be synchronized to an external clock. 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.

RT8011/Aoperation in forced continuous PWM Mode which minimizes ripple voltage and reduces the noise and RF interference.

100% duty cycle in Low Dropout Operation further maximize battery life.

Ordering Information

RT8011/A

Package Type

F : MSOP-10 (RT8011)

QW : WDFN-10L 3x3 (RT8011)

QW : WDFN-8EL 3x3 (RT8011A)

Lead Plating System

P : Pb Free

G : Green (Halogen Free and Pb Free)

Without SYNC and PGOOD Function

With SYNC and PGOOD Function

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

zHigh Efficiency : Up to 95%

zLow RDS(ON) Internal Switches : 110mΩ

zProgrammable Frequency : 300kHz to 4MHz

zNo Schottky Diode Required

z0.8V Reference Allows Low Output Voltage

zForced Continuous Mode Operation

zLow Dropout Operation : 100% Duty Cycle

zSynchronizable Switching Frequency (For RT8011 Only)

zPower Good Output Voltage Monitor (For RT8011 Only)

zRoHS Compliant and 100% Lead (Pb)-Free

Applications

zPortable Instruments

zBattery-Powered Equipment

zNotebook Computers

zDistributed Power Systems

zIP Phones

zDigital Cameras

Pin Configurations

(TOP VIEW)

SHDN/RT			10		COMP
SYNC		2	9		FB
GND		3	8		PGOOD
LX		4	7		VDD
PGND		5	6		PVDD

MSOP-10

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

Marking Information

For marking information, contact our sales representative directly or through a Richtek distributor located in your area.

DS8011/A-02 March 2011

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1

RT8011/A

Typical Application Circuit

VIN
2.6V to 5.5V						R	CCOMP
R		RT8011
						COMP	1000pF
OSC						13k
332k	1 SHDN/RT		COMP	10
	2 SYNC		FB	9	RPGOOD		R2 240k
	3 GND		PGOOD	8	100k
	4 LX		VDD	7
	5 PGND		PVDD	6	CIN	R1		C1
						510k
					22uF			22pF
			L1
		2.2uH							VOUT
							COUT
									2.5V/2A
							22uF
Figure 1. Typical Application Circuit for RT8011
VIN
2.6V to 5.5V
R		RT8011A				RCOMP	CCOMP
OSC						13k	1000pF
332k	1 SHDN/RT		COMP	8
	2	GND	FB	7			R2	240k
	3 LX		VDD	6
	4 PGND		PVDD	5	CIN		R1
							510k
					22uF
			L1
		2.2uH							VOUT
							COUT
									2.5V/2A
							22uF

Figure 2. Typical Application Circuit for RT8011A

Note : Using all Ceramic Capacitors

Table 1

Component Supplier	Series	Inductance (μH)	DCR (mΩ)	Current Rating (mA)	Dimensions (mm)
TAIYO YUDEN	NR 4018	2.2	60	2700	4x4x1.8
Sumida	CDRH4D28	2.2	31.3	2040	4.5x4.5x3
GOTREND	GTSD53	2.2	29	2410	5x5x2.8
ABC	SR0403	2.2	47	2600	4.5x4x3.2

Table 2

Component Supplier	Part No.	Capacitance (μF)	Case Size
TDK	C3225X5R0J226M	22	1210
TDK	C3225X5R0J226M	22	1210
TDK	C2012X5R0J106M	10	0805
Panasonic	ECJ4YB0J226M	22	1210
Panasonic	ECJ4YB1A226M	22	1210
Panasonic	ECJ4YB1A106M	10	1210
TAIYO YUDEN	LMK325BJ226ML	22	1210
TAIYO YUDEN	JMK316BJ226ML	22	1206
TAIYO YUDEN	JMK212BJ106ML	10	0805
www.richtek.com			DS8011/A-02 March 2011

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RT8011/A

Layout Guide

CIN must be placed between

VDD and GND as closer as possible

	VIN		C		IN			GND
								RT8011
	PVDD				6			5
	VDD				7			4
				8				3
	PGOOD
					9
	FB							2

Output capacitor must

be near RT8011

LX should be

VOUT

connected to

COUT

Inductor by wide

and short trace,

keep sensitive

L1

compontents away

PGND

from this trace

LX

GND

VIN

SYNC

R1	COMP	10	1	SHDN/RT
CF	R2 RCOMP			ROSC
VOUT	CCOMP
			GND

Connect the FB pin directly to feedback resistors. The

resistor divider must be connected between VOUT and GND.

Figure 3. RT8011 Layout Guide

R1

CF

VOUT

CIN must be placed between

Output capacitor must

VDD and GND as closer as

be near RT8011A

possible

LX should be

VIN

CIN

GND

C

OUT VOUT

connected to

Inductor by wide

and short trace,

RT8011A

keep sensitive

L1

compontents away

PVDD

5

4

PGND

from this trace

VDD

6

3

LX

FB

2

GND

7

8

COMP

1

SHDN/RT

R2 RCOMP

ROSC

CCOMP

GND

Connect the FB pin directly to feedback resistors. The

resistor divider must be connected between VOUT and GND.

Figure 4. RT8011A Layout Guide

Functional Pin Description

	Pin Number		Pin Name		Pin Function
	RT8011	RT8011A
				Oscillator Resistor Input. Connecting a resistor to ground from this pin sets
	1	1	SHDN/RT	the switching frequency. Forcing this pin to VDD causes the device to be shut
				down.
				External Clock Synchronization Input. The oscillation frequency can be
	2	--	SYNC	synchronized to an external oscillation applied to this pin. When tied to VDD,
				internal oscillator is selected.
	3	2	GND	Signal Ground. All small-signal components and compensation components
				should connect to this ground, which in turn connects to PGND at one point.
	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 (−) terminal of CIN and COUT.
	6	5	PVDD	Power Input Supply. Decouple this pin to PGND with a capacitor.
	7	6	VDD	Signal Input Supply. Decouple this pin to GND with a capacitor. Normally VDD
				is equal to PVDD.
	8	--	PGOOD	Power Good Indicator. Open-drain logic output that is pulled to ground when
				the output voltage is not within	±12.5% of regulation point.
	9	7	FB	Feedback Pin. Receives the	feedback voltage from a resistive divider
				connected across the output.
				Error Amplifier Compensation Point. The current comparator threshold
	10	8	COMP	increases with this control voltage. Connect external compensation elements
				to this pin to stabilize the control loop.

DS8011/A-02 March 2011

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RT8011/A

Function Block Diagram

		SHDN/RT
		SD		ISEN		PVDD
SYNC		OSC	Slope
			Com
COMP
0.8V	EA	Output		OC
FB		Clamp		Limit
	Int-SS				Driver	LX
		0.9V		Control
				Logic
		0.7V
					NISEN	PGND
POR					NMOS I Limit
		0.4V
						PGOOD
			VREF	OTP		GND
VDD
			RT8011
		SHDN/RT
		SD

ISEN PVDD

	OSC	Slope
		Com

COMP

0.8V	EA	Output		OC
FB		Clamp		Limit
	Int-SS			Driver	LX
		0.9V	Control
			Logic
		0.7V
				NISEN	PGND
POR				NMOS I Limit
		0.4V
		VREF	OTP		GND

VDD

RT8011A

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DS8011/A-02 March 2011

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RT8011/A

Operation

Main Control Loop

The RT8011/A is a monolithic, constant-frequency, current mode step-down DC/DC converter. During normal operation, the internal top power switch (P-Channel MOSFET) is turned on at the beginning of each clock cycle. Current in the inductor increases until the peak inductor current reach the value defined by the voltage on the COMP pin. The error amplifier adjusts the voltage on the COMP pin by comparing the feedback signal from a resistor divider on the FB pin with an internal 0.8V reference. When the load current increases, it causes a reduction in the feedback voltage relative to the reference. The error amplifier raises the COMP voltage until the average inductor current matches the new load current. When the top power MOSFET shuts off, the synchronous power switch (N-Channel MOSFET) turns on until either the bottom current limit is reached or the beginning of the next clock cycle.

The operating frequency is set by an external resistor connected between the RT pin and ground. The practical switching frequency can range from 300kHz to 4MHz. Power Good comparators will pull the PGOOD output low if the output voltage comes out of regulation by 12.5%. In an over-voltage condition, the top power MOSFET is turned off and the bottom power MOSFET is switched on until either the over-voltage condition clears or the bottom MOSFET's current limit is reached.

Frequency Synchronization

The internal oscillator of the RT8011 can be synchronized to an external clock connected to the SYNC pin. The frequency of the external clock can be in the range of 300kHz to 4MHz. For this application, the oscillator timing resistor should be chosen to correspond to a frequency that is about 20% lower than the synchronization frequency.

Dropout Operation

When the input supply voltage decreases toward the output voltage, the duty cycle increases toward the maximum on-time. Further reduction of the supply voltage forces the main switch to remain on for more than one cycle eventually reaching 100% duty cycle.

The output voltage will then be determined by the input voltage minus the voltage drop across the internal P-Channel MOSFET and the inductor.

Low Supply Operation

The RT8011/A is designed to operate down to an input supply voltage of 2.6V. One important consideration at low input supply voltages is that the RDS(ON) of the P-Channel and N-Channel power switches increases. The user should calculate the power dissipation when the RT8011/A is used at 100% duty cycle with low input voltages to ensure that thermal limits are not exceeded.

Slope Compensation and Inductor Peak Current

Slope compensation provides stability in constant frequency architectures by preventing sub-harmonic oscillations at duty cycles greater than 50%. It is accomplished internally by adding a compensating ramp to the inductor current signal. Normally, the maximum inductor peak current is reduced when slope compensation is added. In the RT8011/A, however, separated inductor current signals are used to monitor over current condition. This keeps the maximum output current relatively constant regardless of duty cycle.

Short-Circuit Protection

When the output is shorted to ground, the inductor current decays very slowly during a single switching cycle. A current runaway detector is used to monitor inductor current. As current increasing beyond the control of current loop, switching cycles will be skipped to prevent current runaway from occurring.

DS8011/A-02 March 2011

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RT8011/A

Absolute Maximum Ratings		(Note 1)
z Supply Input Voltage, VDD, PVDD ----------------------------------------------------------------------------				−0.3V to 6V
z LX Pin Switch Voltage --------------------------------------------------------------------------------------------				−0.3V to (PVDD + 0.3V)
z Other I/O Pin Voltages -------------------------------------------------------------------------------------------				−0.3V to (VDD + 0.3V)
z LX Pin Switch Current --------------------------------------------------------------------------------------------				4A
z Power Dissipation, PD @ TA = 25°C
MSOP-10 ------------------------------------------------------------------------------------------------------------				467mW
WDFN-10L 3x3 -----------------------------------------------------------------------------------------------------				909mW
WDFN-8EL 3x3 ----------------------------------------------------------------------------------------------------				909mW
z Package Thermal Resistance (Note 2)
MSOP-10, θJA ------------------------------------------------------------------------------------------------------				214°C/W
WDFN-10L 3x3, θJA -----------------------------------------------------------------------------------------------				110°C/W
WDFN-8EL 3x3, θJA -----------------------------------------------------------------------------------------------				110°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 Mode) --------------------------------------------------------------------------------------				2kV
MM (Machine Mode) ----------------------------------------------------------------------------------------------				200V
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 Voltage	VFB		0.784	0.8		0.816		V
DC Bias Current		Active , VFB = 0.78V, Not Switching	--	460		--		μA
		Shutdown	--	--		1		μA
Output Voltage Line Regulation		VIN = 2.7V to 5.5V	--	0.04		--		%/V
Output Voltage Load Regulation		0A < ILOAD < 2A	--	0.25		--		%
Error Amplifier	gm		--	800		--		μs
Transconductance
Current Sense Transresistance	RT		--	0.4		--		Ω
Power Good Range			--	±12.5		±15		%
Power Good Pull-Down			--	--		120		Ω
Resistance
						To be continued
www.richtek.com				DS8011/A-02 March 2011

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