Richtek RT8004GCP, RT8004GQV, RT8004PCP, RT8004PQV Schematic [ru]

RT8004

3A, 4MHz, Synchronous Step-Down Regulator

General Description

The RT8004 is a high efficiency synchronous, step-down DC/DC converter. Its input voltage range is from 2.65V 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 power switch with 75mΩ on-resistance increases efficiency and eliminates 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. External compensation allows the transient response to be optimized over a wide range of loads and output capacitors.

The RT8004 operates in Forced Continuous Mode which reduces noise and RF interference. 100% duty cycle in Low Dropout Operation further maximize battery life.

Ordering Information

RT8004

Package Type

CP : TSSOP-16 (Exposed Pad)

QV : VQFN-16L 4x4 (V-Type)

Lead Plating System

P : Pb Free

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.

Marking Information

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

Features

zHigh Efficiency : Up to 95%

zLow Quiescent Current : 100μA

zLow RDS(ON) Internal Switches : 75mΩ

zProgrammable Frequency : 300kHz to 4MHz

zNo Schottky Diode Required

z0.8V Reference Allows Low Output Voltage

zLow Dropout Operation : 100% Duty Cycle

zSynchronizable Switching Frequency

zPower Good Output Voltage Monitor

zOver Temperature Protection

zThermally Enhanced TSSOP-16 (Exposed Pad) and 16-Lead VQFN 4x4 Packages

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)

	PGOOD	VDD	PVDD	LX
	16 15 14 13
COMP	1				12	LX
FB	2	GND			11	PGND
RT	3				10	PGND
			17
SYNC	4				9	LX
	5	6	7	8
	EN/SS	GND	PVDD	LX
	VQFN-16L 4x4

	VDD			16	PVDD
	PGOOD	2		15	LX
	COMP	3		14	LX
	FB	4	GND	13	PGND
	RT	5		12	PGND
	SYNC	6	17 11		LX
	EN/SS	7		10	LX
	GND	8		9	PVDD

TSSOP-16 (Exposed Pad)

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RT8004

Typical Application Circuit

VIN

				2.65V to 5.5V
	RPG			47uF
100k
		VDD
PGOOD		RT8004		C1
		PGOOD	R1
				22pF
CTH	RTH		510k
1000pF			L1
	10k	COMP
			1uH	VOUT
	R2		LX
				2.5V/3A
	240k	FB
	ROCS			COUT
	309k	RT		47uF
			PVDD
External Clock		SYNC	CIN1
RSS			10uF
4.7M		EN/SS	PVDD
	CSS
				CIN2
	470pF
		GND	10uF
			PGND

Functional Pin Description

	Pin No.		Pin Name	Pin Function
	RT8004PCP	RT8004PQP
	1	15	VDD	Signal Input Supply. Decouple this pin to GND with a	capacitor.
				Normally VDD is equal to PVDD.
	2	16	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.
				Error Amplifier Compensation Pin. The current comparator threshold
	3	1	COMP	increases with this control voltage. Connect external compensation
				elements to this pin to stabilize the control loop.
	4	2	FB	Feedback Pin. Receives the feedback voltage from a resistive divider
				connected across the output.
	5	3	RT	Oscillator Resistor Input. Connecting a resistor to ground from this pin
				sets the switching frequency.
				External Clock Synchronization Input. The internal oscillator can be
	6	4	SYNC	synchronized to an external clock applied to this pin. If not use, please
				connect this pin to VDD or GND.
				Enable Control and Soft-Start Input. Forcing this pin below 0.5V shuts
	7	5	EN/SS	down the RT8004. In shutdown all functions are disabled drawing < 1μA
				of supply current. A capacitor to ground from this pin sets the ramp time
				to full output current.
	8,	6,		Signal Ground. All small-signal components, compensation components
	Exposed Pad	Exposed Pad	GND	and the exposed pad on the bottom side of the IC should connect to this
	(17)	(17)		ground, which in turn connects to PGND at one point.
	9, 16	7, 14	PVDD	Power Input Supply. Decouple this pin to PGND with a capacitor.
	10,11,	8, 9, 12, 13	LX	Internal Power MOSFET Switches Output. Connect this	pin to the
	14, 15			inductor.
	12, 13	10, 11	PGND	Power Ground. Connect this pin close to the terminal of CIN and COUT.
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RT8004

Function Block Diagram

			RT
						ISEN		PVDD
SYNC	ExtSyn		Oscillator		Slope Com
COMP
	0.8V		Output			OC
		EA				Limit		LX
FB			Clamp
							Driver
EN/SS	Ext_SS		SD	0.9V		Control
	Int_SS					Logic
				0.7V
							NISEN	PGND
				0.4V
							NMOS I Limit
	POR		POR		0.8V			PGOOD
				BG	VREF	OTP
	VDD	GND

Operation

Main Control Loop

The RT8004 is a monolithic, constant-frequency, current mode step-down DC/DC converter. During normal operation, the internal top power switch (P-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 bottom current limit is set at −2A.

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 overvoltage condition clears or the bottom MOSFET’ s current limit is reached.

Frequency Synchronization

The internal oscillator of the RT8004 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.

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RT8004

Dropout Operation

When the input supply voltage decreases toward the output voltage, the duty cycle increases toward the maximum ontime. 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-MOSFET and the inductor.

Low Supply Operation

The RT8004 is designed to operate down to an input supply voltage of 2.65V. One important consideration at low input supply voltages is that the RDS(ON) of the P-MOSFET and N-MOSFET power switches increases. The user should calculate the power dissipation when the RT8004 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 subharmonic 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 RT8004, however, separated inductor current signals are used to monitor over current condition and minimum peak current. This keeps the maximum output current and minimum peak 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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DS8004-07 March 2011

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						RT8004
Absolute Maximum Ratings		(Note 1)
z Supply Input Voltage ----------------------------------------------------------------------------------------------					−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 Power Dissipation, PD @ TA = 25°C
TSSOP-16-----------------------------------------------------------------------------------------------------------					2.66W
VQFN-16L 4x4 -----------------------------------------------------------------------------------------------------					2.315W
z Package Thermal Resistance (Note 2)
TSSOP-16, θJA -----------------------------------------------------------------------------------------------------					47°C/W
VQFN-16L 4x4, θJA ------------------------------------------------------------------------------------------------					54°C/W
VQFN-16L 4x4, θJC -----------------------------------------------------------------------------------------------					7°C/W
z Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------------					260°C
z Junction Temperature ---------------------------------------------------------------------------------------------					150°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 ----------------------------------------------------------------------------------------------					2.65V to 5.5V
z Ambient Temperature Range ------------------------------------------------------------------------------------					−40°C to 85°C
z Junction Temperature Range ------------------------------------------------------------------------------------					−40°C to 125°C
Electrical Characteristics
(VDD = 3.3V, TA = 25°C, unless otherwise specified)
Parameter	Symbol		Test Conditions	Min	Typ		Max		Unit
Input Voltage Range	VDD			2.65	--		5.5		V
Feedback Voltage	VFB		(Note 5)	0.784	0.8		0.816		V
Feedback Leakage Current	IFB			--	--		0.4		μA
			Active, VFB = 0.78V,	180	400		520		μA
Input DC Bias Current			Not switching
			Shutdown, VEN < 0.1V (Note 5)	--	--		1		μA
Reference Voltage Line Regulation			VIN = 2.7V to 5.5V (Note 5)	--	0.04		0.5		%/V
			Measured in Servo Loop,						%
Output Voltage Load Regulation			VCOMP = 1.2V to 1.6V	--	0.05		+/-0.2
			(Note 5)
Power Good
Power Good Range				--	±12.5		±15		%
Power Good Pull-Down Resistance				--	--		120		Ω
Switching Frequency	fOSC		ROSC = 309k	0.8	1		1.2		MHz
			Switching Frequency Range	0.3	--		4		MHz
Sync Frequency Range			(Note 6)	0.3	--		4		MHz
							To be continued
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