Richtek RT8015AGQW Schematic [ru]

3A, 2MHz, Synchronous Step-Down Converter

RT8015A

General Description

The RT8015A is a high efficiency synchronous, step-down
DC/DC converter. Its input voltage range is from 2.6V to

5.5V and provides a n 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 or can be synchronized to an
external clock. 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 opti mized over a wide
range of loads a nd output ca pacitors.

The RT8015A is operated in forced continuous PWM Mode
which minimizes ripple voltage a nd reduces the noise and
RF interference.

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

Features

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High Efficiency : Up to 95%

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z Low R

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z Programmable Frequency : 300kHz to 2MHz

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z No Schottky Diode Required

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z 0.8V Reference Allows for Low Output Voltage

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z Forced Continuous Mode Operation

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z Low Dropout Operation : 100% Duty Cycle

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

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Internal Switches : 110m

DS(ON)

ΩΩ

Ω

ΩΩ

Applications

z Portable Instruments
z Battery-Powered Equipment
z Notebook Computers
z Distributed Power Systems
z IP Phones
z Digital Camera s

Pin Configurations

(TOP VIEW)

The RT8015A is availa ble in the W DF N-10L 3x3 pa ckage.

Ordering Information

RT8015A

Package Type
QW : WDFN-10L 3x3

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.

SHDN/RT

GND

LX
LX

PGND

1
2
3
4
5

10

COMP

9

FB

8

VDD

7

PVDD

9

11

PVDD

WDFN-10L 3x3

Marking Information

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

DS8015A-04 March 2011 www.richtek.com

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RT8015A

Typical Application Circuit

V

IN

5V

R

OSC

332k

Note : Using all Ceramic Capacitors

Functional Pin Description

1
2

3, 4

5

SHDN/RT
GND

LX

PGND

RT8015A

L1

2µH

COMP

FB

VDD

PVDD

10

9
8

6, 7

C

IN

22µF

R

COMP

30k

22pF

C

COMP

1000pF

240k

R2

C

1

R1
510k

C

OUT

22µFx2

V

OUT

2.5V/3A

P in No. Pin Name Pin F unction

1 SHDN/RT

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

2 GND

Signal Ground. All small-signal components and compensation components should
connect to this ground, which in turn connects to PGND at one point.

3, 4 LX Internal Power MOSFET Switches Output. Connect this pin to the inductor.

5 PGND Power Ground. Connect this pin close to the negative terminal of CIN and C

6, 7 PVDD Power Input Supply. Decouple this pin to PGND with a capacitor.

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

8 VDD

9 FB

equal to PVDD.
Feedback Pin. This pin Receives the feedback voltage from a resistive divider
connected across the output.
Error Amplifier Compensation Point. The current comparator threshold increases

10 COMP

with this control voltage. Connect external compensation elements to this pin to
stabilize the control loop.
No Internal Connection. The exposed pad must be soldered to a large PCB and

11 (Exposed Pad) NC

connected to GND for maximum power dissipation.

causes the device to be shut down.

DD

OUT

DD

.

is

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Function Block Diagram

RT8015A

SHDN/RT

COMP

FB

0.8V

POR

VDD

EA

Int-SS

SD

Output
Clamp

0.9V

0.7V

0.4V

OSC

Slope

Com

ISEN

OC

Limit

PVDD

Driver

LX

Control

Logic

NISEN

PGND

NMOS I Limit

REF

OTP

GND

V

Layout Guide

CIN must be placed between VDD
and GND as closer as possible

V

IN

PVDD
PVDD

COMP

R1

C

F

V

OUT

R2

R

COMP

C

COMP

VDD

FB

C

6
7
8
9

10

Connect the FB pin directly to feedback resistors. The
resistor divider must be connected between V

GND

IN

RT8015A

GND

Output capacitor must be
near RT8015A

V

and GND.

OUT

OUT

5

PGND

4

LX

3

LX

2

GND

1

SHDN/RT

C

OUT

LX should be
connected to Inductor
by wide and short
trace, keep sensitive
components away

L1

from this trace

R

OSC

DS8015A-04 March 2011 www.richtek.com

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RT8015A

Operation

Main Control Loop

The RT8015A 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 a mplifier 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 rea ched or the beginning of the next clock
cycle.

The operating frequency is set by an external resistor
connected between the RT pin a nd ground. The practical
switching frequency can ra nge from 300kHz to 2MHz. 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 rea ched.

RT8015A 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 a dding a compensating ra mp
to the inductor current signal. Normally, the maximum
inductor peak current is reduced when slope compensation
is added. In the RT8015A, 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 increa sing beyond the control of current
loop, switching cycles will be skipped to prevent current
runaway from occurring.

Dropout Operation

When the input supply voltage decrea ses 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 a nd the inductor.

Low Supply Operation

The RT8015A is designed to operate down to an input
supply voltage of 2.6V. One important consideration at
low input supply voltages is that the R
P-Channel a nd N-Cha nnel power switches increase s. The
user should calculate the power dissipation when the

4

DS(ON)

of the

DS8015A-04 March 2011www.richtek.com

RT8015A

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, P

W D FN-10L 3x3 -----------------------------------------------------------------------------------------------------909mW

z Package Thermal Resistance (Note 2)

W DFN-10L 3x3, θJA-----------------------------------------------------------------------------------------------11 0°C/W

z Junction T emperature--------------------------------------------------------------------------------------------- 150°C
z Lead Temperature (Soldering, 10 sec.)-----------------------------------------------------------------------260°C
z Storage T emperature Range ------------------------------------------------------------------------------------ −65°C to 150°C
z ESD Susceptibility (Note 3)

HBM (Human Body Mode) -------------------------------------------------------------------------------------- 2kV
MM (Ma chine Mode)----------------------------------------------------------------------------------------------200V

Recommended Operating Conditions (Note 4)

z Supply Input V oltage----------------------------------------------------------------------------------------------2.6V to 5.5V
z Junction T emperature Range------------------------------------------------------------------------------------
z Ambient T emperature Range------------------------------------------------------------------------------------

@ TA = 25°C

D

−40°C to 125°C

−40°C to 85°C

Electrical Characteristics

(V

= 3.3V, T

DD

Input Voltage Ra nge VDD 2.6 -- 5.5 V
Feedback Reference Voltage V
Feedback Leakage Current IFB -- 0.1 0.4 μA

DC Bias Cu rre nt

Out put Voltage Line Regul at ion VIN = 2.7V to 5.5V -- 0.04 -- %/V

Out put Voltage Load R egulation

Er ror A mp lifier
Transconductance

Current Sense Transresistance RT -- 0.4 -- Ω
Switching Leakage Current SHDN/RT = VIN = 5. 5V -- -- 1 μA

Switching Fr equenc y

= 25°C, unless otherwise specified)

A

Parameter Symbol Test Conditions Min Typ Max Unit

0.784 0.8 0.816 V

REF

Active , VFB = 0.78V, Not Switching -- 460 -- μA
Shutdown -- -- 1 μA

Me as ured in Se rv o Loop,
V

g

-- 800 -- μs

m

R

= 0.2V to 0.7V (Note 5)

COMP

= 332k 0.8 1 1.2 MHz

OSC

−0.2

±0.02 0.2 %

Switching Fr equency 0.3 -- 2 MHz
Sw itch On Resistan ce, High
Sw itch On Resistan ce, Low R

R

ISW = 0.5A -- 110 160 mΩ

PMOS

ISW = 0.5A -- 110 170 mΩ

NMOS

To be continued

DS8015A-04 March 2011 www.richtek.com

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