Richtek RT8015BGQW Schematic [ru]

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RT8015B

3A, 2MHz, Synchronous Step-Down Converter

General Description

The RT8015B is a high efficiency synchronous, step down DC/DC converter. Its input voltage range is from 2.6V to 5.5V and provides an adjustable regulated output voltage from 0.8V to 5V while delivering up to 3A of output current.

The internal synchronous low on resistance power switches increase efficiency and eliminate the need for an external Schottky diode. The switching frequency is set by an external resistor. The 100% duty cycle provides low dropout operation extending battery life in portable systems. Current mode operation with external compensation allows the transient response to be optimized over a wide range of loads and output capacitors.

The RT8015B is operated in forced continuous PWM Mode which minimizes ripple voltage and reduces the noise and RF interference.

The 100% duty cycle in Low Dropout Operation further maximize battery life.

The RT8015B is available in the WDFN-10L 3x3 and SOP- 8 (Exposed Pad) packages.

Ordering Information

RT8015B

Package Type

QW : WDFN-10L 3x3

SP : SOP-8 (Exposed Pad-Option 2)

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.

Features

zHigh Efficiency : Up to 95%

zLow RDS(ON) Internal Switches : 110mΩ

zProgrammable Frequency : 300kHz to 2MHz

zNo Schottky Diode Required

z0.8V Reference Allows for Low Output Voltage

zForced Continuous Mode Operation

zLow Dropout Operation : 100% Duty Cycle

zPower Good Output Voltage Indicator

zRoHS Compliant and Halogen Free

Applications

zPortable Instruments

zBattery-Powered Equipment

zNotebook Computers

zDistributed Power Systems

zIP Phones

zDigital Cameras

Pin Configurations

(TOP VIEW)

SHDN/RT 1

 

 

10

COMP

GND 2

 

 

9

FB

LX 3

 

 

8

PGOOD

LX 4

 

 

7

VDD

PGND 5

 

11

9

PVDD

WDFN-10L 3x3

SHDN/RT

 

 

8

COMP

GND

2

GND

7

FB

LX

3

6

VDD

PGND

4

9

5

PVDD

 

SOP-8 (Exposed Pad)

Marking Information

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

DS8015B-04 March 2011

www.richtek.com

 

1

RT8015B

 

 

 

 

 

 

 

 

 

 

 

Typical Application Circuit

 

 

 

 

 

L1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VIN

 

 

 

RT8015B

LX

3, 4

2.2µH

 

VOUT

 

 

6

PVDD

 

 

 

 

 

2.5V/3A

5V

 

 

 

 

 

 

 

CF

R1

 

 

R3

 

 

 

 

 

 

 

CIN

 

 

 

 

 

 

 

 

 

1

 

 

 

 

 

 

22pF

510k

COUT

22µF

R4

7 VDD

 

FB 9

 

 

 

 

 

 

 

 

 

22µF x 2

 

100k

C1

 

 

 

 

 

RCOMP

CCOMP

 

 

 

 

0.1µF

 

 

 

 

 

R2

 

 

 

 

 

COMP 10

27k

1nF

 

PGOOD

 

 

8 PGOOD

 

240k

 

 

ROSC

 

 

 

 

 

 

 

 

GND 2

 

 

 

 

 

 

332k

1 SHDN/RT

 

 

 

 

 

 

 

 

 

 

PGND 5

 

 

 

 

Note : Using all Ceramic Capacitors

Table 1. Recommended Component Selection

VOUT (V)

R1 (kΩ)

R2 (kΩ)

RCOMP (kΩ)

CCOMP (nF)

L1 (μH)

COUT (μF)

3.3

750

240

30

1

2.2

22 x 2

2.5

510

240

27

1

2.2

22 x 2

1.8

300

240

22

1

2.2

22 x 2

 

 

 

 

 

 

 

1.5

210

240

18

1

2.2

22 x 2

1.2

120

240

15

1

1.0

22 x 2

 

 

 

 

 

 

 

1.0

60

240

13

1

1.0

22 x 2

Functional Pin Description

Pin No.

Pin Name

 

Pin Function

 

 

 

WDFN

SOP-8

 

-10L 3x3

(Exposed Pad)

 

 

 

 

 

 

 

Oscillator Resistor Input. Connecting a resistor to ground from this

1

1

SHDN/RT

pin sets the switching frequency. Forcing this pin to VDD causes the

 

 

 

device to be shut down.

 

 

 

 

 

Signal Ground. All small

signal components and compensation

2

2

GND

components should connect to this ground, which in turn connects to

 

 

 

PGND at one point.

 

 

3, 4

3

LX

Internal Power MOSFET Switches Output. Connect this pin to the

inductor.

 

 

 

 

 

 

 

5

4

PGND

Power Ground. Connect this pin close to the negative terminal of CIN

and COUT.

 

 

 

 

 

 

 

6

5

PVDD

Power Input Supply. Decouple this pin to PGND with a capacitor.

 

 

 

 

7

6

VDD

Signal Input Supply. Decouple this pin to GND with a capacitor.

Normally VDD is equal to PVDD.

 

 

 

 

 

 

 

 

Power Good Indicator. This pin is open

drain logic output that is

8

--

PGOOD

pulled to ground when the output voltage is not within ±12.5% of

 

 

 

regulation point.

 

 

9

7

FB

Feedback Pin. This pin

receives the

feedback voltage from a

resistive divider connected across the output.

 

 

 

 

 

 

Error Amplifier Compensation Point. The current comparator

10

8

COMP

threshold increases with this control voltage. Connect external

 

 

 

compensation elements to this pin to stabilize the control loop.

11

--

(Exposed Pad)

No Internal Connection. The exposed pad must be soldered to a

 

 

 

large PCB and connected to GND for maximum power dissipation.

--

9

GND

The exposed pad must be soldered to a large PCB and connected to

GND for maximum power dissipation.

 

 

 

 

 

 

 

 

 

 

 

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DS8015B-04 March 2011

2

Richtek RT8015BGQW Schematic

RT8015B

Function Block Diagram

 

 

SHDN/RT

 

 

 

 

 

 

SD

 

ISEN

 

PVDD

 

 

 

 

 

 

 

 

 

 

 

 

 

OSC

Slope

 

 

 

 

 

Com

 

 

 

 

 

 

 

 

 

COMP

 

 

 

 

 

 

0.8V

EA

Output

 

OC

 

 

FB

Clamp

 

Limit

 

 

 

 

 

 

 

Int-SS

 

 

 

Driver

LX

 

 

0.9V

 

Control

 

 

 

 

 

 

 

 

 

 

Logic

 

 

 

 

0.7V

 

 

NISEN

PGND

 

 

 

 

 

 

 

 

 

 

NMOS I Limit

POR

 

0.2V

 

 

 

 

 

 

 

PGOOD

 

 

 

 

 

 

 

 

VREF

OTP

 

 

GND

VDD

 

 

 

 

 

 

Layout Guide

VIN

R3

C1

GND

CF R1

VOUT

Place the input and output capacitors as close to the IC as possible.

 

 

GND

 

COUT

 

 

CIN

 

Bottom Layer

RT8015B

 

 

R4

PVDD 6

 

5

PGND

VDD 7

 

4

LX

 

 

 

PGOOD 8

 

3

LX

 

FB 9

 

2

GND

 

COMP 10

1

SHDN/RT

R2 RCOMP

 

 

 

 

CCOMP

 

 

 

 

 

GND

 

 

Place the feedback and compensation components as close to the IC as possible.

VOUT

LX should be

 

 

connected to Inductor

 

 

by wide and short

 

 

trace, keep sensitive

L1

components away

 

 

from this trace

 

 

 

 

ROSC

DS8015B-04 March 2011

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3

RT8015B

Operation

Main Control Loop

The RT8015B is a monolithic, constant-frequency, current mode step-down DC/DC converter. During normal operation, the internal top power switch (P-Channel MOSFET) is turned on at the beginning of each clock cycle. Current in the inductor increases until the peak inductor current reach the value defined by the voltage on the COMP pin. The error amplifier adjusts the voltage on the COMP pin by comparing the feedback signal from a resistor divider on the FB pin with an internal 0.8V reference. When the load current increases, it causes a reduction in the feedback voltage relative to the reference. The error amplifier raises the COMP voltage until the average inductor current matches the new load current. When the top power MOSFET shuts off, the synchronous power switch (N-MOSFET) turns on until either the bottom current limit is reached or the beginning of the next clock cycle.

The operating frequency is set by an external resistor connected between the RT pin and ground. The practical switching frequency can range from 300kHz to 2MHz.

Dropout Operation

When the input supply voltage decreases toward the output voltage, the duty cycle increases toward the maximum on-time. Further reduction of the supply voltage forces the main switch to remain on for more than one cycle eventually reaching 100% duty cycle.

The output voltage will then be determined by the input voltage minus the voltage drop across the internal P-Channel MOSFET and the inductor.

Low Supply Operation

The RT8015B is designed to operate down to an input supply voltage of 2.6V. One important consideration at low input supply voltages is that the RDS(ON) of the P-Channel and N-Channel power switches increases. The user should calculate the power dissipation when the RT8015B is used at 100% duty cycle with low input voltages to ensure that thermal limits are not exceeded.

Slope Compensation and Inductor Peak Current

Slope compensation provides stability in constant frequency architectures by preventing sub-harmonic oscillations at duty cycles greater than 50%. It is accomplished internally by adding a compensating ramp to the inductor current signal. Normally, the maximum inductor peak current is reduced when slope compensation is added. In the RT8015B, however, separated inductor current signals are used to monitor over current condition. This keeps the maximum output current relatively constant regardless of duty cycle.

Short Circuit Protection

When the output is shorted to ground, the inductor current decays very slowly during a single switching cycle. A current runaway detector is used to monitor inductor current.As current increasing beyond the control of current loop, switching cycles will be skipped to prevent current runaway from occurring.

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DS8015B-04 March 2011

4

 

 

 

 

RT8015B

Absolute Maximum Ratings

(Note 1)

 

 

 

 

 

 

z Supply Input Voltage, VDD, PVDD ----------------------------------------------------------------------------

 

 

−0.3V to 6V

 

z LX Pin Switch Voltage --------------------------------------------------------------------------------------------

 

 

 

−0.3V to (PVDD + 0.3V)

<200ns ---------------------------------------------------------------------------------------------------------------

 

 

 

−5V to 7.5V

 

z Other I/O Pin Voltages -------------------------------------------------------------------------------------------

 

 

 

−0.3V to (VDD + 0.3V)

z LX Pin Switch Current --------------------------------------------------------------------------------------------

 

 

 

4A

 

 

 

z Power Dissipation, PD @ TA = 25°C

 

 

 

 

 

 

 

SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------------

 

 

 

1.333W

 

WDFN-10L 3x3 -----------------------------------------------------------------------------------------------------

 

 

 

1.429W

 

z Package Thermal Resistance (Note 2)

 

 

 

 

 

 

 

SOP-8 (Exposed Pad), θJA -------------------------------------------------------------------------------------

 

 

 

75°C/W

 

SOP-8 (Exposed Pad), θJC -------------------------------------------------------------------------------------

 

 

 

15°C/W

 

WDFN-10L 3x3, θJA -----------------------------------------------------------------------------------------------

 

 

 

70°C/W

 

WDFN-10L 3x3, θJC -----------------------------------------------------------------------------------------------

 

 

 

8.2°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 Input Voltage ----------------------------------------------------------------------------------------------

 

 

 

2.6V to 5.5V

 

z Junction Temperature Range ------------------------------------------------------------------------------------

 

 

 

−40°C to 125°C

 

z Ambient Temperature Range ------------------------------------------------------------------------------------

 

 

 

−40°C to 85°C

 

Electrical Characteristics

 

 

 

 

 

 

 

(VDD = 3.3V, TA = 25°C, unless otherwise specified)

 

 

 

 

 

 

Parameter

Symbol

Test Conditions

Min

Typ

 

Max

 

Unit

 

 

 

 

 

 

 

 

 

Input Voltage Range

VDD

 

2.6

--

 

5.5

 

V

Feedback Reference Voltage

VREF

 

0.784

0.8

 

0.816

 

V

Feedback Leakage Current

IFB

 

--

0.1

 

0.4

 

μA

DC Bias Current

 

Active , VFB = 0.78V, Not Switching

--

460

 

--

 

μA

 

Shutdown

--

--

 

1

 

μA

 

 

 

 

 

 

 

 

 

 

 

 

 

Output Voltage Line Regulation

 

VIN = 2.7V to 5.5V

--

0.03

 

--

 

%/V

 

 

 

 

 

 

 

 

 

Output Voltage Load Regulation

 

Measured in Servo Loop,

−0.2

±0.02

 

0.2

 

%

 

VCOMP = 0.2V to 0.7V (Note 5)

 

 

 

 

 

 

 

 

 

 

Error Amplifier

gm

 

--

800

 

--

 

μs

Transconductance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Current Sense Transresistance

RT

 

--

0.4

 

--

 

Ω

Switching Leakage Current

 

SHDN/RT = VIN = 5.5V

--

--

 

1

 

μA

 

 

 

 

 

 

 

 

 

 

 

 

 

 

To be continued

 

 

 

 

 

 

 

 

DS8015B-04 March 2011

 

 

 

 

 

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5

RT8015B

Parameter

Symbol

Test Conditions

Min

Typ

Max

Unit

 

 

 

 

 

 

 

Switching Frequency

 

ROSC = 332k

0.8

1

1.2

MHz

 

Switching Frequency

0.3

--

2

MHz

 

 

 

 

 

 

 

 

 

Switch On Resistance, High

RPMOS

ISW = 0.5A

--

110

160

 

 

 

 

 

 

 

Switch On Resistance, Low

RNMOS

ISW = 0.5A

--

110

170

Power Good Range

 

 

--

±12.5

±15

%

 

 

 

 

 

 

 

Power Good Pull-Down

 

 

--

--

120

Ω

Resistance

 

 

 

 

 

 

 

 

Peak Current Limit

ILIM

 

3.2

3.8

--

A

 

 

 

 

 

 

 

Under Voltage Lockout

 

VDD Rising

--

2.4

--

V

Threshold

 

VDD Falling

--

2.3

--

V

 

 

Shutdown Threshold

 

 

--

VIN − 0.7

VIN − 0.4

V

 

 

 

 

 

 

 

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 natural convection at TA = 25°C on a high-effective thermal conductivity four-layer test board of JEDEC 51-7 thermal measurement standard. The measurement case position of θJC is on the exposed pad of the packages.

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

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

Note 5. The specifications over the -40°C to 85°C operation ambient temperature range are assured by design, characterization and correlation with statistical process controls.

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DS8015B-04 March 2011

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