Richtek RT8015GSP, RT8015PSP Schematic [ru]

2A, 2MHz, Synchronous Step-Down Regulator

RT8015

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.

Features

l High Efficiency : Up to 95%
l Low R

l Programmable Frequency : 300kHz to 2MHz

l No Schottky Diode Required
l 0.8V Reference Allows Low Output Voltage
l Forced Continuous Mode Operation
l Low Dropout Operation : 100% Duty Cycle
l RoHS Compliant and 100% Lead (Pb)-Free

Internal Switches : 110mΩ

DS(ON)

Applications

l Portable Instruments
l Battery-Powered Equipment
l Notebook Computers
l Distributed Power Systems
l IP Phones
l Digital Cameras

Pin Configurations

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 require-

ments of IPC/JEDEC J-STD-020.

} Suitable for use in SnPb or Pb-free soldering processes.

(TOP VIEW)

SHDN/RT

GND

PGND

2
3

LX

4

SOP-8 (Exposed Pad)

GND

8

COMP

7

FB

6

VDD

9

5

PVDD

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RT8015

Typical Application Circuit

L1

2.6V to 5.5V

V

IN

C

IN

22uF

R

OSC

332k

5

PVDD

6

VDD

4

PGND

1

SHDN/RT

RT8015

LX

FB

COMP

GND

Note : Using all Ceramic Capacitors

Recommended Component for Different Output V oltage Applications

V

L1 (uH) C

OUT

(uF) R1 (kΩ) R2 (kΩ) R

OUT

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

2.2uH

3

7

R

COMP

8

2,
Exposed
Pad (9)

COMP

13k

(kΩ) C

C

COMP

1nF

COMP

(nF)

R1
510k

R2
240k

C

OUT

22uF

V

OUT

2.5V/2A

Functional Pin Description

Pin No. Pin Name Pin Fu nction

1 SHDN/RT

2,

9 (Ex posed Pad)

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 C
5 PVDD Power Input Supply. Decouple this pin to PGND with a capac itor.

6 VDD

7 FB

8 COMP

GND

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

Signal Ground. All small-signal components and compensation components should
connect to this ground, which in turn connects to PGND at one point. The exposed
pad must be soldered to a large P CB and connected to GND for maximum power
dissipation.

Signal Input Supply. Decouple this pin to GND with a capacitor. Normally V
equal to PVD D.
Feedback Pin. Receives the feedback voltage from a resistive divider connected
across the output.
Error Amplifier Compensation Point. The current comparator threshold increases
with this control voltage. Connect external compensation elements to this pin to
stabilize the control loop.

causes the device to be shut down.

DD

OUT

.

is

DD

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Function Block Diagram

RT8015

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

Driver

Control

Logic

NISEN

NMOS I Limit

REF

OTP

V

PVDD

LX

PGND

GND

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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.

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 R
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.

of the P-Channel and

DS(ON)

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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RT8015

Absolute Maximum Ratings (Note 1)

l Supply Input Voltage, VDD, PVDD---------------------------------------------------------------------------−0.3V to 6V
l LX Pin Switch Voltage------------------------------------------------------------------------------------------−0.3V to (PVDD + 0.3V)
l Other I/O Pin Voltages------------------------------------------------------------------------------------------−0.3V to (VDD + 0.3V)
l LX Pin Switch Current-------------------------------------------------------------------------------------------4A
l Power Dissipation, P

SOP-8 (Exposed Pad)-----------------------------------------------------------------------------------------1.33W

l Package Thermal Resistance (Note 2)

SOP-8 (Exposed Pad), θJA------------------------------------------------------------------------------------75°C/W
SOP-8 (Exposed Pad), θJC------------------------------------------------------------------------------------15°C/W

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

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

Recommended Operating Conditions (Note 4)

@ TA = 25°C

D

l Supply Input Voltage--------------------------------------------------------------------------------------------2.6V to 5.5V
l Junction Temperature Range----------------------------------------------------------------------------------
l Ambient Temperature Range----------------------------------------------------------------------------------

−40°C to 125°C

−40°C to 85°C

Electrical Characteristics

(V

= 3.3V, T

DD

Input Voltage Range VDD 2.6 -- 5.5 V
Feedback Reference Voltage V

DC Bias Current

Output Voltage Line Regulation VIN = 2.7V to 5.5V -- 0.04 -- %/V
Output Voltage Load Regulation 0A < I

Error Amplifier
Transconductance

Current Sense Transresistance RT -- 0.4 -- Ω
Power Good Range -- ±12.5 ±15 %

Power Good Pull-Down
Resistance

Switching Frequency

= 25°C, unless otherwise specified)

A

Parameter Symbol

0.784 0.8 0.816

REF

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

gm -- 800 -- us

-- -- 120 Ω
R

Switching Frequency 0.3 -- 2 MHz

Test Conditions Min Typ Max Unit

< 2A -- 0.25 -- %

LOAD

= 332k 0.8 1 1.2 MHz

OSC

V

Sync Frequency Range 0.3 -- 2 MHz

To be continued

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