Richtek RT9261B-18PB, RT9261B-28GX, RT9261B-28PB, RT9261B-28PX, RT9261B-30GB Schematic [ru]

RT9261B

VFM Step-Up DC/DC Converter

General Description

The RT9261B Series are VFM Step-up DC/DC converter ICs with ultra low supply current by CMOS process and suitable for use with battery-powered instruments.

The RT9261B IC consists of an oscillator, a VFM control circuit, a driver transistor (LX switch), a reference voltage unit, an error amplifier, resistors for voltage detection, and a LX switch protection circuit.Alow ripple and high efficiency step-up DC/DC converter can be constructed with the RT9261B IC and only three external components.

The EN pin enables the circuit to set the standby supply current at a maximum of 0.5μA.

Features

zMinimal Number of External Components (Only an Inductor, a Diode, and a Capacitor)

zUltra Low Input Current (6.5μA at Switch Off)

zCapable of Supplying 50mA Output Current with Internal Switch

z± 2% Output Voltage Accuracy

zLow Ripple and Low Noise

zLow Start-up Voltage, 0.8V at 1mA

z80% Efficiency with Low Cost Inductor

z+50 ppm/°C Low Temperature-Drift

zSOT-89 and SOT-23-5 Small Packages

zRoHS Compliant and 100% Lead (Pb)-Free

Ordering Information

RT9261B-

Package Type

B : SOT-23-5

X : SOT-89

Lead Plating System P : Pb Free

G : Green (Halogen Free and Pb Free)

Output Voltage 15 : 1.5V

16 : 1.6V

:

49 : 4.9V

50 : 5.0V

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.

Applications

zPower source for battery-powered equipment

zPower source for cameras, camcorders, VCRs, PDAs, pagers, electronic data banks, and hand-held communication equipment

zPower source for appliances, which require higher voltage than that of batteries used in the appliances

Pin Configurations

(TOP VIEW)

LX GND

5 4

2 3

EN VOUT NC

SOT-23-5

Marking Information

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

1

2

3

GND VOUT LX (TAB)

SOT-89

DS9261B-16 April 2011	www.richtek.com
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RT9261B

Typical Application Circuit

	D1
	1N5819
L1	RT9261B
LX	VOUT	VOUT
	GND	+
VIN		COUT
		22µF

			D1
			1N5819
	L1	LX	RT9261B
			VOUT	VOUT
				+
	VIN	EN	GND	COUT
				22µF

* L1 ranges from 27μH to 120μH

Functional Pin Description

	Pin No.		Pin Name	Pin Function
	SOT-23-5	SOT-89
	1	--	EN	Chip Enable (Active High).
	2	2	VOUT	Output Voltage.
	3	--	NC	No Internal Connection.
	4	1	GND	Ground.
	5	3	LX	Pin for Switching.

Function Block Diagram

LX		VLX Limiter	VREF
	LXSW
		Buffer	VOUT
GND			-
		OSC 190kHz
			+
			Error
			Amplifier
		Chip Enable
		EN

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DS9261B-16 April 2011

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							RT9261B
Absolute Maximum Ratings
z Output Voltage ------------------------------------------------------------------------------------------------------							8V
z LX Pin Voltage -------------------------------------------------------------------------------------------------------							8V
z EN Pin Voltage(1) ----------------------------------------------------------------------------------------------------							−0.3 to VOUT +0.3V
z LX Pin Output Current ---------------------------------------------------------------------------------------------							400mA
z Power Dissipation, PD @ TA = 25°C
SOT-89 ----------------------------------------------------------------------------------------------------------------							0.5W
SOT-23-5--------------------------------------------------------------------------------------------------------------							0.25W
z Package Thermal Resistance
SOT-89, θJC ----------------------------------------------------------------------------------------------------------							100°C/W
SOT-89, θJA ----------------------------------------------------------------------------------------------------------							300°C/W
SOT-23-5, θJA --------------------------------------------------------------------------------------------------------							250°C/W
z Operating Temperature Range -----------------------------------------------------------------------------------							−20 to +85°C
z Storage Temperature Range --------------------------------------------------------------------------------------							−65°C to 150°C
z Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------							260°C
Notes: (1) Applicable to RT9261B-xxCB
Electrical Characteristics (Refer to Figure 1)
Parameter	Symbol		Test Conditions			Min	Typ		Max		Unit
Output Voltage Accuracy	VOUT					-2	--		+2		%
Input Voltage	VIN					--	--		7		V
Start-up Voltage	VST	IOUT = 1mA, VIN: 0 → 2V				--	0.8		1		V
Hold-on Voltage	VHO	IOUT = 1mA, VIN: 2 → 0V				0.7	--		--		V
Input Current 1		VIN in continuous			VOUT ≤ 3.5V (1)	--	24		36		μA
		switching			3.5V < VOUT ≤ 5V (2)	--	36		45
Input Current 2 (1) (2)		VOUT in switch off condition				--	6.5		10		μA
Input Current 3 (guaranteed by		V	in no load		VOUT ≤ 3.5V (1)	--	18		36		μA
I1 and I2)					3.5V < VOUT ≤ 5V (2)	--	20		45
		IN
LX Switching Current	ISWITCHING	VLX = 0.4V			VOUT ≤ 3.5V (1)	120	--		--		mA
					3.5V < VOUT ≤ 5V (2)	160	--		--
LX Leakage Current	ILEAKAGE	VLX = 6V				--	--		0.5		μA
Maximum Oscillator Frequency	FMAX	VOUT = 2.5V to 5V				140	190		240		kHz
		VOUT = 1.5V to 2.4V				140	190		320		kHz
Oscillator Duty Cycle	DOSC	On (VLX “L”) side			VOUT = 2.5V to 5V	65	75		85		%
					VOUT = 1.5V to 2.4V	60	70		80		%
Efficiency						--	80		--		%
VLX Voltage Limit		LX switch on				0.65	0.8		1.0		V

Notes:

(1)VIN = 1.8V, VSS = 0V, IOUT = 1mA, Topt = 25°C, and use External Circuit of Typical Application

(2)VIN = 3V, VSS = 0V, IOUT = 1mA, Topt= 25°C, and External Circuit of Typical Application

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