Richtek RT8259GE, RT8259GJ6, RT8259PE Schematic [ru]

RT8259

1.2A, 24V, 1.4MHz Step-Down Converter

General Description

The RT8259 is a high voltage buck converter that can support the input voltage range from 4.5V to 24V and the output current can be up to 1.2A. Current Mode operation provides fast transient response and eases loop stabilization.

The chip also provides protection functions such as cycle- by-cycle current limiting and thermal shutdown protection. The RT8259 is available in a SOT-23-6 and TSOT-23-6 packages.

Ordering Information

RT8259

Package Type E : SOT-23-6 J6 : TSOT-23-6

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.

Marking Information

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

Features

zWide Operating Input Voltage Range : 4.5V to 24V

zAdjustable Output Voltage Range : 0.8V to 15V

z1.2A Output Current

z0.3Ω Internal Power MOSFET Switch

zHigh Efficiency up to 92%

z1.4MHz Fixed Switching Frequency

zStable with Low ESR Output Ceramic Capacitors

zThermal Shutdown

zCycle-By-Cycle Over Current Protection

zRoHS Compliant and Halogen Free

Applications

zDistributed Power Systems

zBattery Charger

zPre-Regulator for Linear Regulators

zWLEDDrivers

Pin Configurations

(TOP VIEW)

PHASE VIN EN

6 5 4

2 3

BOOT GND FB

SOT-23-6/TSOT-23-6

Typical Application Circuit

VIN

4.5V to 24V

5

VIN

BOOT

1

VOUT

C1

CB

L1

3.3V

RT8259

10µF

6

10nF

4.7µH

PHASE

D1

R1

Chip Enable

4

B230A

EN

FB

3

62k

C2

Open =

GND

R2

22µF

Automatic Startup

2

19.6k

DS8259-03 March 2011	www.richtek.com
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RT8259

Table 1. Recommended Component Selection, C2 = 22μF

VOUT (V)	1.2	1.8	2.5	3.3	5	8	10	15
L1 (μH)	2	2	3.6	4.7	6.8	10	10	15
R1 (kΩ)	62	62	62	62	62	68	68	68
R2 (kΩ)	124	49.9	29.4	19.6	12	7.5	5.9	3.9

Functional Pin Description

	Pin No.	Pin Name	Pin Function
			Bootstrap. A capacitor is connected between PHASE and BOOT pins to form a floating
	1	BOOT	supply across the power switch driver. This capacitor is needed to drive the power switch‘s
			gate above the supply voltage.
			Ground. This pin is the voltage reference for the regulated output voltage. For this reason,
	2	GND	care must be taken in its layout. This node should be placed outside of the D1 to C1 ground
			path to prevent switching current spikes from inducing voltage noise into the part.
	3	FB	Feedback. An external resistor divider from the output to GND tapped to the FB pin sets the
			output voltage. The value of the divider resistors also set loop bandwidth.
	4	EN	Chip Enable (Active High). If the EN pin is open, it will be pulled to high by internal circuit.
	5	VIN	Supply Voltage. Bypass VIN to GND with a suitable large capacitor to prevent large voltage
			spikes from appearing at the input.
	6	PHASE	Switch Output.

Function Block Diagram

VIN						X20		-
1µA
					Current Sense Amp			+
								25mΩ
			Regulator	Ramp
				Generator
10k	1.1V	-		Oscillator				BOOT
		+
EN				1.4MHz		S
3V	Shutdown		Reference
	Comparator					Q	Driver
					+
			+			R
					- PWM
FB			- EA					PHASE
				30pF	Comparator		Bootstrap
			400k
					OC Limit Clamp		Control
GND
			1pF

www.richtek.com

DS8259-03 March 2011

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	RT8259
Absolute Maximum Ratings (Note 1)
z Supply Voltage, VIN ------------------------------------------------------------------------------------------------	26V
z PHASE Voltage -----------------------------------------------------------------------------------------------------	−0.3V to (VIN + 0.3V)
z BOOT Voltage -------------------------------------------------------------------------------------------------------	VPHASE + 6V
z All Other Pins--------------------------------------------------------------------------------------------------------	0.3V to 6V
z Output Voltage ------------------------------------------------------------------------------------------------------	−0.3V to 15V
z Power Dissipation, PD @ TA = 25°C
T/SOT-23-6 -----------------------------------------------------------------------------------------------------------	0.4W
z Package Thermal Resistance (Note 2)
T/SOT-23-6, θJA ------------------------------------------------------------------------------------------------------	250°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 Voltage, VIN ------------------------------------------------------------------------------------------------	4.5V to 24V
z Output Voltage, VOUT ----------------------------------------------------------------------------------------------	0.8V to 15V
z EN Voltage, VEN -----------------------------------------------------------------------------------------------------	0V to 5.5V
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
Feedback Reference Voltage			VFB	4.5V ≤ VIN ≤ 24V	0.784	0.8	0.816	V
Feedback Current			IFB	VFB = 0.8V	--	0.1	0.3	μA
Switch On Resistance			RDS(ON)		--	0.3	--	Ω
Switch Leakage				VEN = 0V, VPHASE = 0V	--	--	10	μA
Current Limit			ILIM	VBOOT − VPHASE = 4.8V	1.6	2.1	--	A
Oscillator Frequency			fSW		1.2	1.4	1.6	MHz
Maximum Duty Cycle					--	80	--	%
Minimum On-Time			tON		--	100	--	ns
Under Voltage Lockout				Rising	3.9	4.2	4.5	V
Threshold
Under Voltage Lockout					--	200	--	mV
Threshold Hysteresis
EN Input Voltage		Logic-High	VIH		1.4	--	--	V
		Logic-Low	VIL		--	--	0.4
EN Pull Up Current				VEN = 0V	--	1	--	μA
							To be continued
DS8259-03 March	2011						www.richtek.com
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RT8259

Parameter	Symbol	Test Conditions	Min	Typ	Max	Unit
Shutdown Current	ISHDN	VEN = 0V	--	25	--	μA
Quiescent Current	IQ	VEN = 2V, VFB = 1V (Not Switching)	--	0.55	1	mA
Thermal Shutdown	TSD		--	150	--	°C

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 the natural convection at TA = 25°C on a high effective four layers thermal conductivity test board of JEDEC 51-7 thermal measurement standard.

Note 3. Devices are ESD sensitive. Handling precaution is recommended.

Note 4. The device is not guaranteed to function outside its operating conditions.

www.richtek.com	DS8259-03 March 2011
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RT8259

Typical Operating Characteristics

Efficiency vs. Load Current

	100									VIN = 12V
	90
	80									VIN = 24V
(%)	70
	60
Efficiency	50
	40
	30
	20
	10									VOUT = 5V
	0
	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1	1.1	1.2

Efficiency vs. Load Current

	100
	90									VIN = 12V
	80									VIN = 24V
	70
(%)
	60
Efficiency
	50
	40
	30
	20
	10								VOUT = 3.3V
	0
	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1	1.1	1.2

Load Current (A)	Load Current (A)
Output Voltage vs. Load Current	Output Voltage vs. Temperature

	3.333													3.38
	3.328													3.36
(V)	3.323												(V)	3.34
Output Voltage	3.318		VIN = 24V										Output Voltage	3.32
														3.30
	3.313		VIN = 12V											3.28
	3.308													3.26
	3.303													3.24
	3.298													3.22
	0	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1	1.1	1.2

						VIN = 24V
						VIN = 12V
						IOUT = 0A
-50	-25	0	25	50	75	100	125

Load Current (A)	Temperature (°C)
Frequency vs. Input Voltage	Frequency vs. Temperature

	1.55									1.55
	1.50									1.50
(MHz)	1.45								(MHz)	1.45
	1.40									1.40
Frequency	1.35								Frequency	1.35
	1.30									1.30
	1.25									1.25
	1.20				VOUT = 3.3V, IOUT = 0.3A					1.20
	1.15									1.15
	4	6.5	9	11.5	14	16.5	19	21.5	24

			VIN = 12V, VOUT = 3.3V, IOUT = 0.3A
-50	-25	0	25	50	75	100	125

Input Voltage (V)	Temperature (°C)
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