Richtek RT8259GE, RT8259GJ6, RT8259PE Schematic [ru]

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

RT8259

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 tra nsient response a nd ea ses loop sta bilization.

The chip also provides protection functions such a s cycle­by-cycle current limiting and thermal shutdown prote ction.
The RT8259 is available in a SOT-23-6 and TSOT-23-6
pack ages.

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 require-

ments of IPC/JEDEC J-STD-020.

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

Features

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Wide Operating Input Voltage Range : 4.5V to 24V

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z Adjustable Output Voltage Range : 0.8V to 15V

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z 1.2A Output Current

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ΩΩ

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z 0.3

Ω Internal Power MOSFET Switch

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ΩΩ

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z High Efficiency up to 92%

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z 1.4MHz Fixed Switching Frequency

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z Stable with Low ESR Output Ceramic Ca pacitors

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z Thermal Shutdown

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z Cycle-By-Cycle Over Current Protection

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z RoHS Compliant and Halogen Free

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Applications

z Distributed Power Systems
z Battery Charger
z Pre-Regulator for Linear Regulators
z WLED Drivers

Pin Configurations

(TOP VIEW)

ENVINPHASE

4

56

Marking Information

23

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

BOOT GND FB

SOT-23-6/TSOT-23-6

Typical Application Circuit

V

IN

4.5V to 24V
V

R1
62k

R2

19.6k

OUT

3.3V

C2

22µF

C1
10µF

Chip Enabl e

Open =
Automatic Startu p

5

VIN

RT8259

PHASE

4

EN

GND

2

BOOT

FB

1

CB

10nF

6

D1
B230A

3

L1

4.7µH

DS8259-03 March 2011 www.richtek.com

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RT8259

Table 1. Recommended Component Selection, C2 = 22

V

(V) 1.2 1.8 2.5 3.3 5 8 10 15

OUT

μμ

μF

μμ

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. P in Nam e Pin Funct io n

Bootstrap. A capacitor is connected between PHASE and BOOT pins to form a floating

1 BOOT

2 GND

3 FB
4 EN
5 VIN
6 PHASE Switch Output.

supply across the power switch driver. This capacitor is needed to drive the power switch‘s
gate abov e the supply voltage .

Ground. This pin is the voltage reference for the regulated output voltage. For this reason,
care must be taken in its layout. This node should be placed outside of the D1 to C1 ground
pa th to pre ven t switching curr ent spikes fr om i n ducing v olta g e noise into the part.

Feedback. An exter nal resistor divide r from the output to GND tapp ed to the FB pin sets the
output vol tag e. The valu e of the divider resisto rs also set loop bandwidth.

Chip Enabl e (Active High). If the EN pin is open, it will be p ulled to high by internal circuit.
Supply Volt age. Byp ass VIN to GND with a suita ble large capacitor to prevent large voltage

spikes from appea ring at the input.

Function Block Diagram

VIN

1µA

­+

Shutdown

Comparator

EN

FB

GND

10k

1.1V

3V

Regulator

Reference

400k

Ramp

Generator

Oscillator

1.4MHz

+

EA

­30pF

1pF

Current Sense Amp

S

+

­PWM

Comparator

OC Limit Clamp

Q

R

X20

Driver

Bootstrap

Control

­+

25mΩ

Ω

BOOT

PHASE

DS8259-03 March 2011www.richtek.com

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Absolute Maximum Ratings (Note 1)

RT8259

z Supply V oltage, V
z PHASE V oltage ----------------------------------------------------------------------------------------------------- −0.3V to (V
z BOOT V oltage ------------------------------------------------------------------------------------------------------- V
z All Other Pins-------------------------------------------------------------------------------------------------------- 0.3V to 6V
z Output V oltage ------------------------------------------------------------------------------------------------------ −0.3V to 15V
z Power Dissipation, P

------------------------------------------------------------------------------------------------ 26V

IN

@ T

D

= 25°C

A

PHASE

+ 6V

+ 0.3V)

IN

T/SOT-23-6 ----------------------------------------------------------------------------------------------------------- 0.4W

z Package Thermal Resistance (Note 2)

T/SOT-23-6, θJA------------------------------------------------------------------------------------------------------ 250°C/W

z Junction T emperature ---------------------------------------------------------------------------------------------- 150°C
z Lead T emperature (Soldering, 10 sec.) ------------------------------------------------------------------------ 260°C
z Storage T emperature 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 V oltage, V
z Output V oltage, V
z EN Voltage, V
z Junction T emperature Range ------------------------------------------------------------------------------------- −40°C to 125°C
z Ambient T emperature Range ------------------------------------------------------------------------------------- −40°C to 85°C

------------------------------------------------------------------------------------------------ 4.5V to 24V

IN

---------------------------------------------------------------------------------------------- 0.8V to 15V

OUT

----------------------------------------------------------------------------------------------------- 0V to 5.5V

EN

Electrical Characteristics

(VIN = 12V, TA = 25° C unless otherwise specified)

Parameter Symbol Test Conditions Min Typ Max Unit

Feedback Reference Voltage VFB 4.5V ≤ V
Feedback Current IFB VFB = 0.8V -- 0.1 0.3 μA
Switch On Resistance R
Switch Lea kage V
Cur rent Limit I

LIM

-- 0.3 -- Ω

DS(ON)

EN

V

BOOT

Oscillator Frequency fSW 1.2 1.4 1.6 MHz
Maximum Duty Cycle -- 80 -- %
Minimum On-Time tON -- 100 -- ns
Under Voltage Lockout
Threshold
Under Voltage Lockout
Threshold Hysteresis

EN Input Voltage

Logic-High VIH 1.4 -- -­Logic-Low V

EN Pull Up Current V

Rising 3.9 4.2 4.5 V

-- 200 -- mV

-- -- 0.4

IL

EN

≤ 24V 0.784 0.8 0.816 V

IN

= 0V, V

− V

PHASE

= 0V -- -- 10 μA

PHASE

= 4.8V 1.6 2.1 -- A

V

= 0V -- 1 -- μA

T o be continued

DS8259-03 March 2011 www.richtek.com

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RT8259

Parameter Symbol Test Conditions Min Typ Max Unit

Shutdown Current I
Quiescent Current IQ V

SHDN

V

EN
EN

= 0V -- 25 -- μA
= 2V, VFB = 1V (Not Switching) -- 0.55 1 mA

Therma l 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. θ

Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.

is measured in the natural convection at TA = 25°C on a high effective four layers thermal conductivity test board of

JA

JEDEC 51-7 thermal measurement standard.

DS8259-03 March 2011www.richtek.com

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Typical Operating Characteristics

RT8259

Efficiency vs. Load Current

100

90
80
70
60
50
40

Efficiency (%)

30
20
10

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 C ur rent (A)

Output Voltage vs. Load Current

3.333

3.328

3.323

Output Vol t ag e (V)

3.318

3.313

3.308

3.303

3.298
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

Load C ur ren t ( A)

VIN = 12V

VIN = 24V

V

= 5V

OUT

Efficiency vs. Load Current

100

90
80
70
60
50
40

Efficiency (%)

30
20
10

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)

Output Voltage vs. Temperature

3.38

3.36

3.34

3.32

3.30

3.28

Output Vol tage ( V)

3.26

3.24

3.22

-50 -25 0 25 50 75 100 125

Temper at ur e (°C)

VIN = 12V

VIN = 24V

V

= 3.3V

OUT

VIN = 24V

VIN = 12V

I

OUT

= 0A

Frequency vs. Input Voltage

1.55

1.50

1.45

1.40

1.35

1.30

Frequency (MHz)

1.25

1.20

V

= 3.3V, I

1.15
4 6.5 9 11.51416.51921.524

Input Vol tage (V)

OUT

OUT

= 0.3A

1.55

1.50

1.45

1.40

1.35

1.30

Frequenc y (MHz) 1

1.25

1.20

1.15

-50 -25 0 25 50 75 100 125

Frequency vs. Temperature

VIN = 12V, V

Temperature (°C)

= 3.3V, I

OUT

OUT

= 0.3A

DS8259-03 March 2011 www.richtek.com

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