RT8290ZSP - Richtek Technology - Datasheet.Directory

RT8290

DS8290-04 October 2016 www.richtek.com

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General Description

The RT8290 is a high efficiency synchronous step-down

DC/DC converter that can deliver up to 3A output current

from 4.5V to 23V input supply. The RT8290's current mode

architecture and external compensation allow the transient

response to be optimized over a wide range of loads and

output capacitors. Cycle-by-cycle current limit provides

protection against shorted outputs and soft-start eliminates

input current surge during start-up. The RT8290 also

provides output under voltage protection and thermal

shutdown protection. The low current (<3μA) shutdown

mode provides output disconnection, enabling easy power

management in battery-powered systems. The RT8290

is awailable in an SOP-8 (Exposed Pad) package.

3A, 23V, 340kHz Synchronous Step-Down Converter

Features



4.5V to 23V Input Voltage Range



1.5% High Accuracy Feedback Voltage



3A Output Current



Integrated N-MOSFET Switches



Current Mode Control



Fixed Frequency Operation : 340kHz



Output Adjustable from 0.925V to 20V



Up to 95% Efficiency



Programmable Soft-Start



Stable with Low-ESR Ceramic Output Capacitors



Cycle-by-Cycle Over Current Protection



Input Under Voltage Lockout



Output Under Voltage Protection



Thermal Shutdown Protection



Thermally Enhanced SOP-8 (Exposed Pad) Package



RoHS Compliant and Halogen Free

Applications

Industrial and Commercial Low Power Systems

Computer Peripherals

LCD Monitors and TVs

Green Electronics/Appliances

Point of Load Regulation of High-Performance DSPs,

FPGAs and ASICs.

Ordering Information

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.

Pin Configurations

(TOP VIEW)

SOP-8 (Exposed Pad)

BOOT

VIN

GND

COMP

GND

Typical Application Circuit

VIN

GND

BOOT

10µH

10nF

22µFx2

26.1k

10k

VOUT

3.3V/3A

10µFx2

VIN

4.5V to 23V RT8290

CSS

0.1µF

COMP

3.9nF RC

6.8k

9 (Exposed Pad)

CBOOT

COUT

CIN

100k

REN

Package Type

SP : SOP-8 (Exposed Pad-Option 1)

RT8290

Lead Plating System

G : Green (Halogen Free and Pb Free)

Z : ECO (Ecological Element with

Halogen Free and Pb free)

RT8290

DS8290-04 October 2016www.richtek.com

Marking Information

RT8290GSP : Product Number

YMDNN : Date Code

Functional Pin Description

Pin No. Pin Name Pin Function

1 BOOT

Bootstrap for High Side Gate Driver. Connect a 10nF or greater ceramic capacitor

from the BOOT pin to SW pin.

2 VIN

Voltage Supply Input. The input voltage range is from 4.5V to 23V. A suitable large

capacitor must be bypassed with this pin.

3 SW Switching Node. Connect the output LC filter between the SW pin and output load.

9 (Exposed Pad) GND Ground. The exposed pad must be soldered to a large PCB and connected to

GND for maximum power dissipation.

5 FB

Output Voltage Feedback Input. The feedback reference voltage is 0.925V

typically.

6 COMP

Compensation Node. This pin is used for compensating the regulation control

loop. A series RC network is required to be connected from COMP to GND. If

needed, an additional capacitor can be connected from COMP to GND.

7 EN

Enable Input. A logic high enables the converter, a logic low forces the converter

into shutdown mode reducing the supply current to less than 3A. For automatic

startup, connect this pin to VIN with a 100k pull up resistor.

8 SS

Soft-Start Control Input. The soft-start period can be set by connecting a capacitor

from SS to GND. A 0.1F capacitor sets the soft-start period to 15.5ms typically.

VOUT (V) R1 (k) R2 (k) RC (k) CC (nF) L (μH) COUT (μF)

15 153 10 30 3.9 33 22 x 2

10 97.6 10 20

3.9 22 22 x 2

8 76.8 10 15

3.9 22 22 x 2

5 45.3 10 13 3.9 15 22 x 2

3.3 26.1 10 6.8

3.9 10 22 x 2

2.5 16.9 10 6.2

3.9 6.8 22 x 2

1.8 9.53 10 4.3

3.9 4.7 22 x 2

1.2 3 10 3 3.9 3.6 22 x 2

Table 1. Recommended Component Selection

RT8290

GSPYMDNN

RT8290ZSP : Product Number

YMDNN : Date Code

RT8290

ZSPYMDNN

RT8290

DS8290-04 October 2016 www.richtek.com

Function Block Diagram

Absolute Maximum Ratings (Note 1)

Supply Voltage, VIN ------------------------------------------------------------------------------------------ −0.3V to 25V

Switching Voltage, SW ------------------------------------------------------------------------------------- −0.3V to (VIN + 0.3V)

SW (AC) 30ns------------------------------------------------------------------------------------------------- −5V to 30V

BOOT Voltage ------------------------------------------------------------------------------------------------- (VSW − 0.3V) to (VSW + 6V)

The Other Pins ------------------------------------------------------------------------------------------------ −0.3V to 6V

Power Dissipation, PD @ TA = 25°C

SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------- 1.333W

Package Thermal Resistance (Note 2)

SOP-8 (Exposed Pad), θJA --------------------------------------------------------------------------------- 75°C/W

SOP-8 (Exposed Pad), θJC -------------------------------------------------------------------------------- 15°C/W

Junction Temperature ---------------------------------------------------------------------------------------- 150°C

Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------ 260°C

Storage Temperature Range ------------------------------------------------------------------------------- −65°C to 150°C

ESD Susceptibility (Note 3)

HBM (Human Body Model) --------------------------------------------------------------------------------- 2kV

MM (Machine Model) ---------------------------------------------------------------------------------------- 200V

Recommended Operating Conditions (Note 4)

Supply Voltage, VIN ------------------------------------------------------------------------------------------ 4.5V to 23V

Enable Voltage, VEN ----------------------------------------------------------------------------------------- 0V to 5.5V

Junction Temperature Range ------------------------------------------------------------------------------- −40°C to 125°C

Ambient Temperature Range ------------------------------------------------------------------------------- −40°C to 85°C

Comparator

Oscillator

Foldback

Control

0.5V

Internal

Regulator

2.5V

Shutdown

Comparator

Current Sense

Amplifier

BOOT

VIN

GND

COMP

VA VCC

Slope Comp

Current

Comparator

7µA

VCC

-EA

0.925V

1.2V

Lockout

Comparator

100m

85m

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Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are

stress ratings only, and 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 may

affect device reliability.

Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is

measured at the exposed pad of the package.

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

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

Electrical Characteristics

Parameter Symbol Test Conditions Min Typ Max Unit

Shutdown Supply Current VEN = 0V -- 0.3 3 A

Supply Current VEN = 3V, VFB = 1V -- 0.8 1.2 mA

Feedback Voltage VFB 4.5V  VIN  23V 0.911 0.925 0.939 V

Error Amplifier Transconductance GEA IC = ±10A -- 940 -- A/V

High Side Switch On-Resistance RDS(ON)1 -- 100 -- m

Low Side Switch On-Resistance RDS(ON)2 -- 85 -- m

High Side Switch Leakage Current VEN = 0V, VSW = 0V -- 0 10 A

Upper Switch Current Limit Min. Duty Cycle

VBOOT  VSW = 4.8V -- 5.1 -- A

Lower Switch Current Limit From Drain to Source -- 1.5 -- A

COMP to Current Sense

Transconductance GCS -- 5.4 -- A/V

Oscillation Frequency fOSC1 300 340 380 kHz

Short Circuit Oscillation Frequency fOSC2 V

FB = 0V -- 100 -- kHz

Maximum Duty Cycle DMAX V

FB = 0.8V -- 90 -- %

Minimum On Time tON -- 100 -- ns

Logic-High VIH 2.7 -- --

EN Input Threshold

Vol ta ge Logic-Low VIL -- -- 0.4

Input Under Voltage Lockout

Threshold VUVLO V

IN Rising 3.8 4.2 4.5 V

Input Under Voltage Lockout

Threshold Hysteresis VUVLO -- 320 -- mV

Soft-Start Current ISS V

SS = 0V -- 6 -- A

Soft-Start Period tSS C

SS = 0.1F -- 15.5 -- ms

Thermal Shutdown TSD -- 150 -- °C

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

RT8290

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Typical Operating Characteristics

Reference Voltage vs. Temperature

0.910

0.915

0.920

0.925

0.930

0.935

0.940

-50 -25 0 25 50 75 100 125

Temperature (C)

Reference Voltage (V)

Reference Voltage vs. Input Voltage

0.920

0.922

0.924

0.926

0.928

0.930

0.932

4 6 8 1012141618202224

Input Voltage (V)

Reference Voltage (V)

Frequency vs. Temperature

300

305

310

315

320

325

330

335

340

345

350

-50 -25 0 25 50 75 100 125

Temperature (C)

Frequency (kHz) 1

VIN = 4.5V

VIN = 12V

VIN = 23V

VOUT = 3.3V, IOUT = 0A

Frequency vs. Input Voltage

300

305

310

315

320

325

330

335

340

345

350

4 6 8 1012141618202224

Input Voltage (V)

Frequency (kHz) 1

VOUT = 3.3V, IOUT = 0A

Output Voltage vs. Output Current

3.300

3.303

3.305

3.308

3.310

3.313

3.315

3.318

3.320

0 0.5 1 1.5 2 2.5 3

Output Current (A)

Output Voltage (V)

VIN = 4.5V

VIN = 12V

VIN = 23V

VOUT = 3.3V

Efficiency vs. Output Current

100

00.511.522.53

Output Current (A)

Efficiency (%)

VIN = 4.5V

VIN = 12V

VIN = 23V

VOUT = 3.3V

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Current Limit vs. Temperature

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

-50 -25 0 25 50 75 100 125

Temprature (C)

Current Limit (A)

VOUT = 3.3V, VIN = 12V

Load Transient Response

Time (100μs/Div)

IOUT

(2A/Div)

VOUT

(200mV/Div)

VIN = 12V, VOUT = 3.3V, IOUT = 0A to 3A

Time (5ms/Div)

Power On from VIN

(2A/Div)

VIN = 12V, VOUT = 3.3V, IOUT = 3A

VIN

(5V/Div)

VOUT

(2V/Div)

Power Off from VIN

Time (5ms/Div)

(2A/Div)

VIN

(5V/Div)

VOUT

(2V/Div)

VIN = 12V, VOUT = 3.3V, IOUT = 3A

Switching Waveform

Time (1μs/Div)

VOUT

(10mV/Div)

VSW

(10V/Div)

VIN = 12V, VOUT = 3.3V, IOUT = 3A

(2A/Div)

Load Transient Response

Time (100μs/Div)

IOUT

(2A/Div)

VOUT

(200mV/Div)

VIN = 12V, VOUT = 3.3V, IOUT = 1.5A to 3A

RT8290

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Power On from EN

Time (10ms/Div)

VIN = 12V, VOUT = 3.3V, IOUT = 3A

IOUT

(2A/Div)

VEN

(2V/Div)

VOUT

(2V/Div)

Power Off from EN

Time (10ms/Div)

IOUT

(2A/Div)

VEN

(2V/Div)

VOUT

(2V/Div)

VIN = 12V, VOUT = 3.3V, IOUT = 3A

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Application Information

The RT8290 is a synchronous high voltage buck converter

that can support the input voltage range from 4.5V to 23V

and the output current can be up to 3A.

Output Voltage Setting

The resistive voltage divider allows the FB pin to sense

the output voltage as shown in Figure 1.

Figure 1. Output Voltage Setting

The output voltage is set by an external resistive voltage

divider according to the following equation :









OUT FB R1

V = V1

where VFB is the feedback reference voltage (0.925V typ.).

External Bootstrap Diode

Connect a 10nF low ESR ceramic capacitor between the

BOOT pin and SW pin. This capacitor provides the gate

driver voltage for the high side MOSFET.

It is recommended to add an external bootstrap diode

between an external 5V and the BOOT pin for efficiency

improvement when input voltage is lower than 5.5V or duty

ratio is higher than 65%. The bootstrap diode can be a

low cost one such as 1N4148 or BAT54.

The external 5V can be a 5V fixed input from system or a

5V output of the RT8290. Note that the external boot

voltage must be lower than 5.5V.

Figure 2. External Bootstrap Diode

Soft-Start

The RT8290 contains an external soft-start clamp that

gradually raises the output voltage. The soft-start timing

Inductor Selection

The inductor value and operating frequency determine the

ripple current according to a specific input and output

voltage. The ripple current ΔIL increases with higher VIN

and decreases with higher inductance.

OUT OUT

LIN

I = 1

fL V

 



 



 

Having a lower ripple current reduces not only the ESR

losses in the output capacitors but also the output voltage

ripple. High frequency with small ripple current can achieve

highest efficiency operation. However, it requires a large

inductor to achieve this goal.

For the ripple current selection, the value of ΔIL = 0.2375

(IMAX) will be a reasonable starting point. The largest ripple

current occurs at the highest VIN. To guarantee that the

ripple current stays below the specified maximum, the

inductor value should be chosen according to the following

equation :

OUT OUT

L(MAX) IN(MAX)

L = 1

fI V

 



 



 

Inductor Core Selection

The inductor type must be selected once the value for L

is known. Generally speaking, high efficiency converters

can not afford the core loss found in low cost powdered

iron cores. So, the more expensive ferrite or

mollypermalloy cores will be a better choice.

The selected inductance rather than the core size for a

fixed inductor value is the key for actual core loss. As the

inductance increases, core losses decrease. Unfortunately,

increase of the inductance requires more turns of wire

and therefore the copper losses will increase.

Ferrite designs are preferred at high switching frequency

due to the characteristics of very low core losses. So,

design goals can focus on the reduction of copper loss

and the saturation prevention.

can be programmed by the external capacitor between

SS pin and GND. The chip provides a 6μA charge current

for the external capacitor. If a 0.1μF capacitor is used to

set the soft-start, the period will be 15.5ms (typ.).

VOUT

RT8290

GND

10nF

RT8290

BOOT

RT8290

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Ferrite core material saturates “hard”, which means that

inductance collapses abruptly when the peak design

current is exceeded. The previous situation results in an

abrupt increase in inductor ripple current and consequent

output voltage ripple.

Do not allow the core to saturate!

Different core materials and shapes will change the size/

current and price/current relationship of an inductor.

Toroid or shielded pot cores in ferrite or permalloy materials

are small and do not radiate energy. However, they are

usually more expensive than the similar powdered iron

inductors. The rule for inductor choice mainly depends

on the price vs. size requirement and any radiated field/

EMI requirements.

CIN and COUT Selection

The input capacitance, CIN, is needed to filter the

trapezoidal current at the source of the high side MOSFET.

To prevent large ripple current, a low ESR input capacitor

sized for the maximum RMS current should be used. The

RMS current is given by :

This formula has a maximum at VIN = 2VOUT, where

IRMS = IOUT/2. This simple worst-case condition is

commonly used for design because even significant

deviations do not offer much relief.

Choose a capacitor rated at a higher temperature than

required. Several capacitors may also be paralleled to

meet size or height requirements in the design.

For the input capacitor, a 10μF x 2 low ESR ceramic

capacitor is recommended. For the recommended

capacitor, please refer to table 3 for more detail.

The selection of COUT is determined by the required ESR

to minimize voltage ripple.

Moreover, the amount of bulk capacitance is also a key

for COUT selection to ensure that the control loop is stable.

Loop stability can be checked by viewing the load transient

response as described in a later section.

The output ripple, ΔVOUT , is determined by :

OUT IN

RMS OUT(MAX) IN OUT

I = I 1



OUT L OUT

VIESR

8fC



 





The output ripple will be highest at the maximum input

voltage since ΔIL increases with input voltage. Multiple

capacitors placed in parallel may be needed to meet the

ESR and RMS current handling requirement. Dry tantalum,

special polymer, aluminum electrolytic and ceramic

capacitors are all available in surface mount packages.

Special polymer capacitors offer very low ESR value.

However, it provides lower capacitance density than other

types. Although Tantalum capacitors have the highest

capacitance density, it is important to only use types that

pass the surge test for use in switching power supplies.

Aluminum electrolytic capacitors have significantly higher

ESR. However, it can be used in cost-sensitive applications

for ripple current rating and long term reliability

considerations. Ceramic capacitors have excellent low

ESR characteristics but can have a high voltage coefficient

and audible piezoelectric effects. The high Q of ceramic

capacitors with trace inductance can also lead to significant

ringing.

Higher values, lower cost ceramic capacitors are now

becoming available in smaller case sizes. Their high ripple

current, high voltage rating and low ESR make them ideal

for switching regulator applications. However, care must

be taken when these capacitors are used at input and

output. When a ceramic capacitor is used at the input

and the power is supplied by a wall adapter through long

wires, a load step at the output can induce ringing at the

input, VIN. At best, this ringing can couple to the output

and be mistaken as loop instability. At worst, a sudden

inrush of current through the long wires can potentially

cause a voltage spike at VIN large enough to damage the

part.

Checking Transient Response

The regulator loop response can be checked by looking

at the load transient response. Switching regulators take

several cycles to respond to a step in load current. When

a load step occurs, VOUT immediately shifts by an amount

equal to ΔILOAD (ESR) and COUT also begins to be charged

or discharged to generate a feedback error signal for the

regulator to return VOUT to its steady-state value. During

this recovery time, VOUT can be monitored for overshoot or

ringing that would indicate a stability problem.

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Thermal Considerations

For continuous operation, do not exceed the maximum

operation junction temperature 125°C. The maximum

power dissipation depends on the thermal resistance of

IC package, PCB layout, the rate of surroundings airflow

and temperature difference between junction to ambient.

The maximum power dissipation can be calculated by

following formula :

PD(MAX) = (TJ(MAX) − TA) / θJA

where TJ(MAX) is the maximum operation junction

temperature, TA is the ambient temperature and the θJA is

the junction to ambient thermal resistance.

For recommended operating conditions specification, the

maximum junction temperature is 125°C. The junction to

ambient thermal resistance θJA is layout dependent. For

SOP-8 (Exposed Pad) package, the thermal resistance

θJA is 75°C/W on the standard JEDEC 51-7 four-layers

thermal test board. The maximum power dissipation at TA

= 25°C can be calculated by following formula :

PD(MAX) = (125°C − 25°C) / (75°C/W) = 1.333W for

SOP-8 (Exposed Pad) package

The maximum power dissipation depends on operating

ambient temperature for fixed TJ(MAX) and thermal

resistance θJA. The derating curve in Figure 3 allows the

designer to see the effect of rising ambient temperature

on the maximum power dissipation.

Layout Considerations

Follow the PCB layout guidelines for optimal performance

of the RT8290.

Keep the traces of the main current paths as short and

wide as possible.

Put the input capacitor as close as possible to the device

pins (VIN and GND).

SW node is with high frequency voltage swing and

should be kept in a small area. Keep sensitive

components away from the SW node to prevent stray

capacitive noise pick-up.

Place the feedback components as close to the FB pin

and COMP pin as possible.

The GND pin and Exposed Pad should be connected to

a strong ground plane for heat sinking and noise

protection.

Figure 3. Derating Curve of Maximum Power Dissipation

VIN

GND

CIN

GND

BOOT

VIN

GND

COMP

GND

VOUT

COUT

Input capacitor must be placed

as close to the IC as possible.

SW should be connected to inductor by

wide and short trace. Keep sensitive

components away from this trace.

The feedback

components must be

connected as close to

the device as possible.

VOUT

Figure 4. PCB Layout Guide

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 25 50 75 100 125

Ambient Temperature (°C)

Maximum Power Dissipation (W) 1

Four-Layer PCB

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Table 3. Suggested Capacitors for CIN and COUT

Component Supplier Series Dimensions (mm)

TDK VLF10045 10 x 9.7 x 4.5

TAIYO YUDEN NR8040 8x8x4

Table 2. Suggested Inductors for Typical Application Circuit

Component Supplier Part No. Capacitance (μF) Case Size

MURATA GRM31CR61E106K 10 1206

TDK C3225X5R1E106K 10 1206

TAIYO YUDEN TMK316BJ106ML 10 1206

MURATA GRM31CR60J476M 47 1206

TDK C3225X5R0J476M 47 1210

TAIYO YUDEN EMK325BJ476MM 47 1210

MURATA GRM32ER71C226M 22 1210

TDK C3225X5R1C226M 22 1210

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Richtek Technology Corporation

14F, No. 8, Tai Yuen 1st Street, Chupei City

Hsinchu, Taiwan, R.O.C.

Tel: (8863)5526789

Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should

obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot

assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be

accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third

parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.

Outline Dimension

EXPOSED THERMAL PAD

(Bottom of Package)

8-Lead SOP (Exposed Pad) Plastic Package

Dimensions In Millimeters Dimensions In Inches

Symbol Min Max Min Max

A 4.801 5.004 0.189 0.197

B 3.810 4.000 0.150 0.157

C 1.346 1.753 0.053 0.069

D 0.330 0.510 0.013 0.020

F 1.194 1.346 0.047 0.053

H 0.170 0.254 0.007 0.010

I 0.000 0.152 0.000 0.006

J 5.791 6.200 0.228 0.244

M 0.406 1.270 0.016 0.050

X 2.000 2.300 0.079 0.091

Option 1 Y 2.000 2.300 0.079 0.091

X 2.100 2.500 0.083 0.098

Option 2 Y 3.000 3.500 0.118 0.138