Richtek RT8004GCP, RT8004GQV, RT8004PCP, RT8004PQV Schematic [ru]

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RT8004

3A, 4MHz, Synchronous Step-Down Regulator

General Description

The RT8004 is a high efficiency synchronous, step-down DC/DC converter. Its input voltage range is from 2.65V 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 power switch with 75mΩ on-resistance increases efficiency and eliminates 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. External compensation allows the transient response to be optimized over a wide range of loads and output capacitors.

The RT8004 operates in Forced Continuous Mode which reduces noise and RF interference. 100% duty cycle in Low Dropout Operation further maximize battery life.

Ordering Information

RT8004

Package Type

CP : TSSOP-16 (Exposed Pad)

QV : VQFN-16L 4x4 (V-Type)

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.

Marking Information

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

Features

zHigh Efficiency : Up to 95%

zLow Quiescent Current : 100μA

zLow RDS(ON) Internal Switches : 75mΩ

zProgrammable Frequency : 300kHz to 4MHz

zNo Schottky Diode Required

z0.8V Reference Allows Low Output Voltage

zLow Dropout Operation : 100% Duty Cycle

zSynchronizable Switching Frequency

zPower Good Output Voltage Monitor

zOver Temperature Protection

zThermally Enhanced TSSOP-16 (Exposed Pad) and 16-Lead VQFN 4x4 Packages

zRoHS Compliant and 100% Lead (Pb)-Free

Applications

zPortable Instruments

zBattery-Powered Equipment

zNotebook Computers

zDistributed Power Systems

zIP Phones

zDigital Cameras

Pin Configurations

(TOP VIEW)

 

PGOOD

VDD

PVDD

LX

 

 

 

16 15 14 13

 

 

COMP

1

 

 

 

12

LX

FB

2

GND

 

11

PGND

RT

3

 

10

PGND

 

17

SYNC

4

 

9

LX

 

 

 

 

5

6

7

8

 

 

 

EN/SS

GND

PVDD

LX

 

 

 

VQFN-16L 4x4

 

VDD

 

 

16

PVDD

PGOOD

2

 

15

LX

COMP

3

 

14

LX

FB

4

GND

13

PGND

RT

5

12

PGND

 

SYNC

6

17 11

LX

EN/SS

7

 

10

LX

GND

8

 

9

PVDD

TSSOP-16 (Exposed Pad)

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RT8004

Typical Application Circuit

VIN

 

 

 

 

2.65V to 5.5V

 

RPG

 

 

47uF

100k

 

 

VDD

 

 

 

 

 

 

PGOOD

 

RT8004

C1

 

PGOOD

R1

 

 

22pF

CTH

RTH

510k

 

 

 

1000pF

 

L1

 

10k

COMP

 

 

 

1uH

VOUT

 

R2

 

LX

 

 

2.5V/3A

 

240k

FB

 

 

 

 

 

 

ROCS

 

 

COUT

 

309k

RT

 

47uF

 

 

PVDD

 

 

 

 

 

External Clock

SYNC

CIN1

 

RSS

 

 

10uF

 

4.7M

 

EN/SS

PVDD

 

 

CSS

 

 

 

 

CIN2

 

470pF

 

 

 

GND

10uF

 

 

 

 

PGND

 

 

 

 

 

Functional Pin Description

Pin No.

Pin Name

Pin Function

 

RT8004PCP

RT8004PQP

 

1

15

VDD

Signal Input Supply. Decouple this pin to GND with a

capacitor.

Normally VDD is equal to PVDD.

 

 

 

 

 

2

16

PGOOD

Power Good Indicator. Open-drain logic output that is pulled to ground

when the output voltage is not within ±12.5% of regulation point.

 

 

 

 

 

 

Error Amplifier Compensation Pin. The current comparator threshold

3

1

COMP

increases with this control voltage. Connect external compensation

 

 

 

elements to this pin to stabilize the control loop.

 

4

2

FB

Feedback Pin. Receives the feedback voltage from a resistive divider

connected across the output.

 

 

 

 

 

 

 

 

 

5

3

RT

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

sets the switching frequency.

 

 

 

 

 

 

 

 

 

 

 

 

External Clock Synchronization Input. The internal oscillator can be

6

4

SYNC

synchronized to an external clock applied to this pin. If not use, please

 

 

 

connect this pin to VDD or GND.

 

 

 

 

Enable Control and Soft-Start Input. Forcing this pin below 0.5V shuts

7

5

EN/SS

down the RT8004. In shutdown all functions are disabled drawing < 1μA

of supply current. A capacitor to ground from this pin sets the ramp time

 

 

 

 

 

 

to full output current.

 

8,

6,

 

Signal Ground. All small-signal components, compensation components

Exposed Pad

Exposed Pad

GND

and the exposed pad on the bottom side of the IC should connect to this

(17)

(17)

 

ground, which in turn connects to PGND at one point.

 

9, 16

7, 14

PVDD

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

10,11,

8, 9, 12, 13

LX

Internal Power MOSFET Switches Output. Connect this

pin to the

14, 15

inductor.

 

 

 

 

12, 13

10, 11

PGND

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

 

 

 

 

 

 

 

 

 

 

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DS8004-07

March 2011

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RT8004

Function Block Diagram

 

 

 

RT

 

 

 

 

 

 

 

 

 

 

 

ISEN

 

PVDD

SYNC

ExtSyn

Oscillator

 

Slope Com

 

 

 

COMP

 

 

 

 

 

 

 

 

 

0.8V

 

Output

 

 

OC

 

 

 

EA

 

 

Limit

 

LX

FB

 

Clamp

 

 

 

 

 

 

 

 

 

Driver

 

 

 

 

 

 

 

 

EN/SS

Ext_SS

 

SD

0.9V

 

Control

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Int_SS

 

 

 

 

Logic

 

 

 

 

 

0.7V

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NISEN

PGND

 

 

 

 

0.4V

 

 

 

 

 

 

 

 

 

NMOS I Limit

 

 

 

 

 

 

 

 

 

 

POR

POR

 

0.8V

 

 

PGOOD

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BG

VREF

OTP

 

 

 

VDD

GND

 

 

 

 

 

Operation

Main Control Loop

The RT8004 is a monolithic, constant-frequency, current mode step-down DC/DC converter. During normal operation, the internal top power switch (P-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 bottom current limit is set at −2A.

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 4MHz.

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 overvoltage condition clears or the bottom MOSFET’ s current limit is reached.

Frequency Synchronization

The internal oscillator of the RT8004 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 4MHz. For this application, the oscillator timing resistor should be chosen to correspond to a frequency that is about 20% lower than the synchronization frequency.

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RT8004

Dropout Operation

When the input supply voltage decreases toward the output voltage, the duty cycle increases toward the maximum ontime. 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-MOSFET and the inductor.

Low Supply Operation

The RT8004 is designed to operate down to an input supply voltage of 2.65V. One important consideration at low input supply voltages is that the RDS(ON) of the P-MOSFET and N-MOSFET power switches increases. The user should calculate the power dissipation when the RT8004 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 subharmonic 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 RT8004, however, separated inductor current signals are used to monitor over current condition and minimum peak current. This keeps the maximum output current and minimum peak 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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RT8004

Absolute Maximum Ratings

(Note 1)

 

 

 

 

 

 

 

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

 

 

 

 

0.3V to 6V

 

 

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

 

 

 

 

0.3V to (PVDD + 0.3V)

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

 

 

 

 

0.3V to (VDD + 0.3V)

z Power Dissipation, PD @ TA = 25°C

 

 

 

 

 

 

 

 

 

 

TSSOP-16-----------------------------------------------------------------------------------------------------------

 

 

 

 

2.66W

 

 

 

 

VQFN-16L 4x4 -----------------------------------------------------------------------------------------------------

 

 

 

 

2.315W

 

 

z Package Thermal Resistance (Note 2)

 

 

 

 

 

 

 

 

 

TSSOP-16, θJA -----------------------------------------------------------------------------------------------------

 

 

 

 

47°C/W

 

 

VQFN-16L 4x4, θJA ------------------------------------------------------------------------------------------------

 

 

 

 

54°C/W

 

 

VQFN-16L 4x4, θJC -----------------------------------------------------------------------------------------------

 

 

 

 

7°C/W

 

 

 

 

z Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------------

 

 

 

260°C

 

 

 

 

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

 

 

 

 

150°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 ----------------------------------------------------------------------------------------------

 

 

 

 

2.65V to 5.5V

 

 

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

 

 

 

 

40°C to 85°C

 

 

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

 

 

 

 

40°C to 125°C

Electrical Characteristics

 

 

 

 

 

 

 

 

 

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

 

 

 

 

 

 

 

Parameter

Symbol

Test Conditions

Min

Typ

 

Max

 

Unit

 

 

 

 

 

 

 

 

 

 

 

 

Input Voltage Range

VDD

 

 

2.65

--

 

5.5

 

V

 

Feedback Voltage

VFB

 

(Note 5)

0.784

0.8

 

0.816

 

V

 

 

 

 

 

 

 

 

 

 

 

 

Feedback Leakage Current

IFB

 

 

--

--

 

0.4

 

μA

 

 

 

 

Active, VFB = 0.78V,

180

400

 

520

 

μA

 

Input DC Bias Current

 

 

Not switching

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Shutdown, VEN < 0.1V (Note 5)

--

--

 

1

 

μA

 

Reference Voltage Line Regulation

 

 

VIN = 2.7V to 5.5V (Note 5)

--

0.04

 

0.5

 

%/V

 

 

 

 

Measured in Servo Loop,

 

 

 

 

 

%

 

Output Voltage Load Regulation

 

 

VCOMP = 1.2V to 1.6V

--

0.05

 

+/-0.2

 

 

 

 

 

(Note 5)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Power Good

 

 

 

 

 

 

 

 

 

 

Power Good Range

 

 

 

--

±12.5

 

±15

 

%

 

 

 

 

 

 

 

 

 

 

 

 

Power Good Pull-Down Resistance

 

 

 

--

--

 

120

 

Ω

 

 

 

 

 

 

 

 

 

 

 

 

Switching Frequency

fOSC

 

ROSC = 309k

0.8

1

 

1.2

 

MHz

 

 

Switching Frequency Range

0.3

--

 

4

 

MHz

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sync Frequency Range

 

 

(Note 6)

0.3

--

 

4

 

MHz

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

To be continued

 

 

 

 

 

 

 

 

 

 

DS8004-07 March 2011

 

 

 

 

 

 

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