Richtek RT8015GSP, RT8015PSP Schematic [ru]

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RT8015

2A, 2MHz, Synchronous Step-Down Regulator

General Description

The RT8015 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 2A of output current.

The internal synchronous low on-resistance power switches increase efficiency and eliminate the need for an external Schottky diode. Switching frequency is set by an external resistor or can be synchronized to an external clock. 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.

RT8015 operation in forced continuous PWM Mode which minimizes ripple voltage and reduces the noise and RF interference. 100% duty cycle in Low Dropout Operation further maximize battery life.

Ordering Information

RT8015

Package Type

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

Lead Plating System P : Pb Free

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

High Efficiency : Up to 95%

Low RDS(ON) Internal Switches : 110mΩ

Programmable Frequency : 300kHz to 2MHz

No Schottky Diode Required

0.8V Reference Allows Low Output Voltage

Forced Continuous Mode Operation

Low Dropout Operation : 100% Duty Cycle

RoHS Compliant and 100% Lead (Pb)-Free

Applications

Portable Instruments

Battery-Powered Equipment

Notebook Computers

Distributed Power Systems

IP Phones

Digital Cameras

Pin Configurations

(TOP VIEW)

SHDN/RT

 

 

8

COMP

GND

2

GND

7

FB

LX

3

9

6

VDD

PGND

4

 

5

PVDD

SOP-8 (Exposed Pad)

DS8015-03 March 2011

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1

RT8015

Typical Application Circuit

 

 

 

 

 

L1

 

 

VIN

RT8015

LX

3

2.2uH

 

VOUT

5 PVDD

 

 

 

 

 

2.5V/2A

2.6V to 5.5V

 

 

 

 

 

 

R1

CIN

6 VDD

 

 

7

 

 

510k

 

FB

 

 

COUT

22uF

 

 

 

8

RCOMP 13k

 

22uF

 

4 PGND

COMP

 

 

 

R2

ROSC

 

 

 

 

 

CCOMP

240k

 

 

 

 

 

1nF

 

332k

1 SHDN/RT

 

GND

2,

 

 

 

 

 

 

 

Exposed

 

 

 

 

 

 

Pad (9)

 

 

Note : Using all Ceramic Capacitors

Recommended Component for Different Output Voltage Applications

VOUT

L1 (uH)

COUT (uF)

R1 (kΩ)

R2 (kΩ)

RCOMP (kΩ)

CCOMP (nF)

3.3V

2.2

22

750

240

13

1

2.5V

2.2

22

510

240

13

1

1.8V

1.0

22

300

240

7.5

1.5

1.2V

1.0

22

120

240

7.5

1.5

Functional Pin Description

Pin No.

Pin Name

Pin Function

1

SHDN/RT

Oscillator Resistor Input. Connecting a resistor to ground from this pin sets the

 

 

switching frequency. Forcing this pin to V

causes the device to be shut down.

 

 

DD

 

 

 

Signal Ground. All small-signal components and compensation components should

2,

GND

connect to this ground, which in turn connects to PGND at one point. The exposed

9 (Exposed Pad)

pad must be soldered to a large PCB and connected to GND for maximum power

 

 

dissipation.

 

3

LX

Internal Power MOSFET Switches Output. Connect this pin to the inductor.

 

 

 

4

PGND

Power Ground. Connect this pin close to the (−) terminal of CIN and COUT.

 

 

 

5

PVDD

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

 

 

 

6

VDD

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

equal to PVDD.

 

 

 

 

7

FB

Feedback Pin. Receives the feedback voltage from a resistive divider connected

across the output.

 

 

 

 

 

 

Error Amplifier Compensation Point. The current comparator threshold increases

8

COMP

with this control voltage. Connect external compensation elements to this pin to

 

 

stabilize the control loop.

 

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DS8015-03 March 2011

2

Richtek RT8015GSP, RT8015PSP Schematic

RT8015

Function Block Diagram

 

 

SHDN/RT

 

 

 

 

 

 

SD

 

ISEN

 

PVDD

 

 

 

 

 

 

 

 

 

 

 

 

 

OSC

Slope

 

 

 

 

 

Com

 

 

 

 

 

 

 

 

 

COMP

 

 

 

 

 

 

0.8V

 

Output

 

OC

 

 

 

 

 

 

 

 

EA

 

Limit

 

 

FB

Clamp

 

 

 

 

 

 

 

 

 

Int-SS

 

 

 

Driver

LX

 

 

0.9V

 

Control

 

 

 

 

 

 

 

 

 

 

Logic

 

 

 

 

0.7V

 

 

 

 

 

 

 

 

 

NISEN

PGND

POR

 

 

 

 

NMOS I Limit

 

0.4V

 

 

 

 

 

 

VREF

OTP

 

GND

VDD

 

 

 

 

 

 

DS8015-03 March 2011

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3

RT8015

Operation

Main Control Loop

The RT8015 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-Channel 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. Power Good comparators will pull the PGOOD output low if the output voltage comes out of regulation by 12.5%. In an over-voltage condition, the top power MOSFET is turned off and the bottom power MOSFET is switched on until either the over-voltage condition clears or the bottom MOSFET's current limit is reached.

Frequency Synchronization

The internal oscillator of the RT8011 can be synchronized to an external clock connected to the SYNC pin. The frequency of the external clock can be in the range of 300kHz to 2MHz. For this application, the oscillator timing resistor should be chosen to correspond to a frequency that is about 20% lower than the synchronization frequency.

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.

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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 RT8015 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 RT8015 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 RT8015, 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.

DS8015-03 March 2011

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RT8015

Absolute Maximum Ratings

(Note 1)

 

 

 

 

 

 

 

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

 

 

0.3V to 6V

 

 

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

 

 

 

0.3V to (PVDD+ 0.3V)

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

 

 

 

0.3V to (VDD + 0.3V)

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

 

 

 

4A

 

 

 

 

Power Dissipation, PD @ TA = 25°C

 

 

 

 

 

 

 

 

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

 

 

 

1.33W

 

 

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 Mode) -------------------------------------------------------------------------------------

 

 

 

2kV

 

 

 

 

MM (Machine Mode) --------------------------------------------------------------------------------------------

 

 

 

200V

 

 

 

 

Recommended Operating Conditions (Note 4)

 

 

 

 

 

 

 

Supply Input Voltage --------------------------------------------------------------------------------------------

 

 

 

2.6V to 5.5V

 

 

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

 

 

 

40°C to 125°C

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

 

DC Bias Current

 

Active , VFB = 0.78V, Not Switching

--

460

 

--

 

μA

 

 

 

 

 

 

 

 

 

 

 

Shutdown

--

--

 

1

 

μA

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Output Voltage Line Regulation

 

VIN = 2.7V to 5.5V

--

0.04

 

--

 

%/V

 

 

 

 

 

 

 

 

 

 

 

Output Voltage Load Regulation

 

0A < ILOAD < 2A

--

0.25

 

--

 

%

 

 

 

 

 

 

 

 

 

 

 

Error Amplifier

gm

 

--

800

 

--

 

us

 

Transconductance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Current Sense Transresistance

RT

 

--

0.4

 

--

 

Ω

 

Power Good Range

 

 

--

±12.5

 

±15

 

%

 

 

 

 

 

 

 

 

 

 

 

Power Good Pull-Down

 

 

--

--

 

120

 

Ω

 

Resistance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switching Frequency

 

ROSC = 332k

0.8

1

 

1.2

 

MHz

 

 

Switching Frequency

0.3

--

 

2

 

MHz

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sync Frequency Range

 

 

0.3

--

 

2

 

MHz

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

To be continued

DS8015-03 March 2011

 

 

 

 

 

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