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

3A, 4MHz, Synchronous Step-Down Regulator

RT8004

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)

Features

High Efficiency : Up to 95%

z Low Quiescent Current : 100

z Low R

z Programmable Frequency : 300kHz to 4MHz

z No Schottky Diode Required

z 0.8V Reference Allows Low Output Voltage

z Low Dropout Operation : 100% Duty Cycle

z Synchronizable Switching Frequency

z Power Good Output Voltage Monitor

z Over Temperature Protection

z Thermally Enhanced TSSOP-16 (Exposed Pad) and

Internal Switches : 75m

DS(ON)

μμ

μA

μμ

ΩΩ

16-Lead VQFN 4x4 Packages

z RoHS Compliant and 100% Lead (Pb)-Free

Applications

z Portable Instruments

z Battery-Powered Equipment

z Notebook Computers

z Distributed Power Systems

z IP Phones

z Digital Cameras

Lead Plating System P : Pb Free 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.

Marking Information

For marking information, contact our sales representative

directly or through a Richtek distributor located in your

area.

Pin Configurations

(TOP VIEW)

PGOOD

VDD

1516

COMP

SYNC

VDD

PGOOD

COMP

SYNC

EN/SS

GND

TSSOP-16 (Exposed Pad)

GND

3 4

GND

EN/SS

VQFN-16L 4x4

2 3 4

GND

5 6 7 8

PVDD

PGND

8765

16 15 14 13 12 11 10

PVDD LX LX PGND PGND LX LX PVDD

DS8004-07 March 2011 www.richtek.com

RT8004

Typical Application Circuit

2.65V to 5.5V

PGOOD

RPG

100k

CTH

1000pF

RTH

10k

External Clock

4.7M

240k

OCS

309k

470pF

VDD

RT8004

PGOOD

COMP

SYNC

EN/SS

GND

PVDD

PGND

510k

1uH

IN1

10uF

IN2

10uF

OUT

47uF

C1 22pF

OUT

2.5V/3A

Functional Pin Description

Pin No.

RT8004PCP RT8004PQP

1 15 VDD

2 16 PGO OD

3 1 COMP

4 2 FB

5 3 RT

6 4 SYNC

7 5 EN/ SS

Exposed Pad

(17)

Exposed Pad

(17)

9, 16 7, 14 PVDD Power Input Supply. Decouple this pin to PGND with a capacitor.

10,11, 14, 15

8, 9, 12, 13 LX

Pin Name Pin Function

Signal Input Supply. Decouple this pin to GND with a capacitor. Norm al ly VDD is equal to P VDD. 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 increases with this control voltage. Connect external compensation elements to this pin to stabilize the control loop.

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

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

External Clock Synchronization Input. The internal oscillator can be 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 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.

Signal Ground. All small-signal components, compensation components

GND

and the exposed pad on the bottom side of the IC should connect to this ground, which in turn connects to PGND at one point.

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

12, 13 10, 11 PGND Power Ground. Connect this pin close to the terminal of CIN and C

DS8004-07 March 2011www.richtek.com

OUT

Function Block Diagram

RT8004

SYNC

COMP

EN/SS

ExtSyn

0.8V

Ext_SS

Int_SS

VDD

POR

GND

Oscillator

Output Clamp

POR

0.9V

0.7V

0.4V

Slope Com

0.8V

REF

Control

Logic

OTP

ISEN

Limit

Driver

NISEN

NMOS I Limit

PVDD

PGND

PGOOD

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.

DS8004-07 March 2011 www.richtek.com

RT8004

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-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 R

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.

of the P-MOSFET and N-MOSFET power switches increases. The user should

DS(ON)

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.

DS8004-07 March 2011www.richtek.com

RT8004

Absolute Maximum Ratings (Note 1)

z Supply Input Voltage ---------------------------------------------------------------------------------------------- −0.3V to 6V z LX Pin Switch Voltage -------------------------------------------------------------------------------------------- −0.3V to (PV z Other I/O Pin Voltages ------------------------------------------------------------------------------------------- −0.3V to (V

z Power Dissipation, P

@ T

= 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

+ 0.3V)

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

= 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

Input DC Bias Current

Reference Voltage Line Regulation V

Output Voltage Load Regulation

Power Good

Active, V Not switching

Shutdown, V

= 2.7V to 5.5V (Note 5) -- 0.04 0.5 %/V

Measured in Servo Loop, V

COMP

(Note 5)

= 0.78V,

< 0.1V (Note 5) -- -- 1 μA

= 1.2V to 1.6V

180 400 520 μA

-- 0.05 +/-0.2 %

Power Good Range -- ±12.5 ±15 % Power Good Pull-Down Resistance -- -- 120 Ω

= 309k 0.8 1 1.2 MHz

Switching Frequency f

OSC

Switching Frequency Range 0.3 -- 4 MHz

Sync Frequency Range (Note 6) 0.3 -- 4 MHz

To be continued

DS8004-07 March 2011 www.richtek.com

+ 10 hidden pages