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

VFM Step-Up DC/DC Converter

RT9261B

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 a n oscillator , a VFM control
circuit, a driver transistor (LX switch), a reference voltage
unit, an error a mplifier , resistors for voltage detection, a nd
a LX switch protection circuit. A low ripple a nd high efficiency
step-up DC/DC converter can be constructed with the
RT9261B IC and only three extern al components.

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

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 require-

ments of IPC/JEDEC J-STD-020.

` Suitable for use in SnPb or Pb-free soldering processes.

Features

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Minimal Number of External Components (Only an

z

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Inductor, a Diode, and a Capacitor)

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z Ultra Low Input Current (6.5

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z Capable of Supplying 50mA Output Current with

μμ

μA at Switch Off)

μμ

Internal Switch

±±

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z

± 2% Output V oltage Accura cy

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±±

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z Low Ripple and Low Noise

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z Low Start-up Voltage, 0.8V at 1mA

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z 80% Efficiency with Low Cost Inductor

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z +50 ppm/°C Low Temperature-Drift

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z SOT-89 and SOT-23-5 Small Packages

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z RoHS Compliant and 100% Lead (Pb)-Free

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Applications

z Power source for battery-powered equipment
z Power source for ca mera s, ca mcorders, VCRs, PDAs,

pagers, electronic data ban ks, and ha nd-held
communication equipment

z Power source for a pplia nces, which require higher

voltage than that of batteries used in the a ppli ances

Pin Configurations

(TOP VIEW)

LX GND

5

EN VOUT NC

SOT-23-5

4

23

Marking Information

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

DS9261B-16 April 2011 www.richtek.com

123

VOUT

GND

(TAB)

LX

SOT-89

1

RT9261B

T ypical Application Circuit

V

IN

V

IN

* L1 ranges from 27μH to 120μH

L1

L1

1N5819

RT9261B

1N5819

RT9261B

LX
EN

D1

GND

D1

GND

VOUTLX

VOUT

+

C

OUT

22µF

+

C

OUT

22µF

V

V

OUT

OUT

Functional Pin Description

Pin No.

SOT-23-5 SOT-89

1 -- EN Chip Enable (Act ive High).
2 2 VOUT Output Voltage.
3 -- NC No Internal Connection.
4 1 GND Ground.
5 3 LX Pin for Switching.

Pin Name Pin Function

Function Block Diagram

LX

LXSW

GND

VLX Limiter

Buffer

OSC 190k H z

Chip Enable

­+

Error

Amplifier

V

REF

VOUT

EN

DS9261B-16 April 2011www.richtek.com

2

RT9261B

Absolute Maximum Ratings

z Output V oltage ------------------------------------------------------------------------------------------------------ 8V
z LX Pin V oltage------------------------------------------------------------------------------------------------------- 8V
z EN Pin Voltage
z LX Pin Output Current --------------------------------------------------------------------------------------------- 400mA
z Power Dissipation, P

SOT-89 ---------------------------------------------------------------------------------------------------------------- 0.5W

SOT-23-5-------------------------------------------------------------------------------------------------------------- 0.25W

z Pack age Thermal Resistance

SOT-89, θJC---------------------------------------------------------------------------------------------------------- 100°C/W
SOT -89, θJA---------------------------------------------------------------------------------------------------------- 300°C/W

SOT-23-5, θJA-------------------------------------------------------------------------------------------------------- 250° C/W

z Operating T emperature Range ----------------------------------------------------------------------------------- −20 to +85°C
z Storage T emperature Range -------------------------------------------------------------------------------------- −65°C to 150°C
z Lead T emperature (Soldering, 10 sec.) ------------------------------------------------------------------------ 260°C

Notes: (1) Applica ble to RT9261B-xxCB

(1)

---------------------------------------------------------------------------------------------------- −0.3 to V

@ TA = 25°C

D

OUT

+0.3V

Electrical Characteristics (Refer to Figure 1)

Parameter Symbol Test Conditions Min Typ Max Unit

Output Voltage Accuracy ΔV
Input Voltage VIN -- -- 7 V
Start-up Voltage VST I
Hold-on Voltage VHO I

Input Current 1
Input Current 2

and I2)

I

1

(1) (2)

V

LX Switching Current I
LX Leakage Current I
Maximum Oscillator Frequency F

Oscillator Duty Cycle D
Efficiency -- 80 -- %

VLX Voltage Limit LX switch on 0.65 0.8 1.0 V

-2 -- +2 %

OUT

= 1mA, VIN: 0 → 2V -- 0.8 1 V

OUT

= 1mA, VIN: 2 → 0V 0.7 -- -- V

OUT

V

in continuous

IN

switching

in switch off condition -- 6.5 10 μA

OUT

V

SWITCHING VLX

LEAKAGE

MAX

OSC

VLX = 6V -- -- 0.5 μA

On (VLX “L”) side

in no load

IN

= 0.4V

V

= 2.5V to 5V 140 190 240 kHz

OUT

V

= 1.5V to 2.4V 140 190 320 kHz

OUT

V

≤ 3.5V

OUT

3.5V < V

V

≤ 3.5V

OUT

3.5V < V
V

≤ 3.5V

OUT

3.5V < V

V

= 2.5V to 5V 65 75 85 %

OUT

= 1.5V to 2.4V 6 0 70 80 %

V

OUT

(1)

-- 24 36

(2)

OUT

OUT

OUT

≤ 5V

≤ 5V

≤ 5V

-- 36 45

(1)

-- 18 36 Input C urrent 3 (guaranteed by

(2)

(1)

-- 20 45

120 -- --

(2)

160 -- --

μA

μA

mA

Notes:

= 1.8V, VSS = 0V, I

(1) V

IN

= 3V, VSS = 0V, I

(2) V

IN

DS9261B-16 April 2011 www.richtek.com

= 1mA, Topt = 25°C, and use External Circuit of Typical Application

OUT

= 1mA, Topt= 25°C, and External Circuit of Typical Application

OUT

3