Richtek RT8015BGQW Schematic [ru]

RT8015B

3A, 2MHz, Synchronous Step-Down Converter

General Description

The RT8015B 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 RT8015B is operated in forced continuous PWM Mode which minimizes ripple voltage and reduces the noise and RF interference.

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

The RT8015B is available in the WDFN-10L 3x3 and SOP- 8 (Exposed Pad) packages.

Ordering Information

RT8015B

Package Type

QW : WDFN-10L 3x3

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.

Features

zHigh Efficiency : Up to 95%

zLow RDS(ON) Internal Switches : 110mΩ

zProgrammable Frequency : 300kHz to 2MHz

zNo Schottky Diode Required

z0.8V Reference Allows for Low Output Voltage

zForced Continuous Mode Operation

zLow Dropout Operation : 100% Duty Cycle

zPower Good Output Voltage Indicator

zRoHS Compliant and Halogen Free

Applications

zPortable Instruments

zBattery-Powered Equipment

zNotebook Computers

zDistributed Power Systems

zIP Phones

zDigital Cameras

Pin Configurations

(TOP VIEW)

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

SOP-8 (Exposed Pad)

Marking Information

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

DS8015B-04 March 2011	www.richtek.com
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RT8015B
Typical Application Circuit								L1
VIN				RT8015B		LX	3, 4	2.2µH			VOUT
			6	PVDD							2.5V/3A
5V									CF	R1
		R3
CIN
		1							22pF	510k	COUT
22µF	R4		7 VDD			FB 9
											22µF x 2
	100k	C1						RCOMP	CCOMP
		0.1µF								R2
					COMP 10			27k	1nF
PGOOD			8 PGOOD							240k
		ROSC
						GND 2
		332k	1 SHDN/RT
					PGND 5

Note : Using all Ceramic Capacitors

Table 1. Recommended Component Selection

VOUT (V)	R1 (kΩ)	R2 (kΩ)	RCOMP (kΩ)	CCOMP (nF)	L1 (μH)	COUT (μF)
3.3	750	240	30	1	2.2	22 x 2
2.5	510	240	27	1	2.2	22 x 2
1.8	300	240	22	1	2.2	22 x 2
1.5	210	240	18	1	2.2	22 x 2
1.2	120	240	15	1	1.0	22 x 2
1.0	60	240	13	1	1.0	22 x 2

Functional Pin Description

	Pin No.		Pin Name		Pin Function
	WDFN	SOP-8
	-10L 3x3	(Exposed Pad)
				Oscillator Resistor Input. Connecting a resistor to ground from this
	1	1	SHDN/RT	pin sets the switching frequency. Forcing this pin to VDD causes the
				device to be shut down.
				Signal Ground. All small	signal components and compensation
	2	2	GND	components should connect to this ground, which in turn connects to
				PGND at one point.
	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	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.
				Power Good Indicator. This pin is open		drain logic output that is
	8	--	PGOOD	pulled to ground when the output voltage is not within ±12.5% of
				regulation point.
	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.
	11	--	(Exposed Pad)	No Internal Connection. The exposed pad must be soldered to a
				large PCB and connected to GND for maximum power dissipation.
	--	9	GND	The exposed pad must be soldered to a large PCB and connected to
				GND for maximum power dissipation.
	www.richtek.com					DS8015B-04 March 2011

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RT8015B

Function Block Diagram

		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
					NMOS I Limit
POR		0.2V
						PGOOD
		VREF	OTP			GND
VDD

Layout Guide

VIN

R3

C1

GND

CF R1

VOUT

Place the input and output capacitors as close to the IC as possible.

		GND		COUT
		CIN
Bottom Layer		RT8015B
R4	PVDD 6		5	PGND
	VDD 7		4	LX
	PGOOD 8		3	LX
	FB 9		2	GND
	COMP 10		1	SHDN/RT
R2 RCOMP
	CCOMP
		GND

Place the feedback and compensation components as close to the IC as possible.

VOUT		LX should be
		connected to Inductor
		by wide and short
		trace, keep sensitive
L1		components away
		from this trace

ROSC

DS8015B-04 March 2011	www.richtek.com
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RT8015B

Operation

Main Control Loop

The RT8015B 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-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 2MHz.

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 RT8015B 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 RT8015B 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 RT8015B, 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.

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DS8015B-04 March 2011

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				RT8015B
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)
<200ns ---------------------------------------------------------------------------------------------------------------				−5V to 7.5V
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
SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------------				1.333W
WDFN-10L 3x3 -----------------------------------------------------------------------------------------------------				1.429W
z Package Thermal Resistance (Note 2)
SOP-8 (Exposed Pad), θJA -------------------------------------------------------------------------------------				75°C/W
SOP-8 (Exposed Pad), θJC -------------------------------------------------------------------------------------				15°C/W
WDFN-10L 3x3, θJA -----------------------------------------------------------------------------------------------				70°C/W
WDFN-10L 3x3, θJC -----------------------------------------------------------------------------------------------				8.2°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 Reference Voltage	VREF		0.784	0.8		0.816		V
Feedback Leakage Current	IFB		--	0.1		0.4		μA
DC Bias Current		Active , VFB = 0.78V, Not Switching	--	460		--		μA
		Shutdown	--	--		1		μA
Output Voltage Line Regulation		VIN = 2.7V to 5.5V	--	0.03		--		%/V
Output Voltage Load Regulation		Measured in Servo Loop,	−0.2	±0.02		0.2		%
		VCOMP = 0.2V to 0.7V (Note 5)
Error Amplifier	gm		--	800		--		μs
Transconductance
Current Sense Transresistance	RT		--	0.4		--		Ω
Switching Leakage Current		SHDN/RT = VIN = 5.5V	--	--		1		μA
						To be continued
DS8015B-04 March 2011						www.richtek.com
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RT8015B

Parameter	Symbol	Test Conditions	Min	Typ	Max	Unit
Switching Frequency		ROSC = 332k	0.8	1	1.2	MHz
		Switching Frequency	0.3	--	2	MHz
Switch On Resistance, High	RPMOS	ISW = 0.5A	--	110	160	mΩ
Switch On Resistance, Low	RNMOS	ISW = 0.5A	--	110	170	mΩ
Power Good Range			--	±12.5	±15	%
Power Good Pull-Down			--	--	120	Ω
Resistance
Peak Current Limit	ILIM		3.2	3.8	--	A
Under Voltage Lockout		VDD Rising	--	2.4	--	V
Threshold		VDD Falling	--	2.3	--	V
Shutdown Threshold			--	VIN − 0.7	VIN − 0.4	V

Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. 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 for extended periods may remain possibility to affect device reliability.

Note 2. θJA is measured in natural convection at TA = 25°C on a high-effective thermal conductivity four-layer test board of JEDEC 51-7 thermal measurement standard. The measurement case position of θJC is on the exposed pad of the packages.

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. The specifications over the -40°C to 85°C operation ambient temperature range are assured by design, characterization and correlation with statistical process controls.

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