Richtek RT7247A User Manual

RT7247A

®

DS7247A-03 October 2016 www.richtek.com

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Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.

©

Design
Tools

Sample &
Buy

Applications

 Wireless AP/Router
 Set-Top-Box
 Industrial and Commerci al Low Power Systems
 LCD Monitors a nd TVs
 Green Electronics/Appliances
 Point of Load Regulation of High-Performance DSPs

2A, 18V, 340kHz Synchronous Step-Down Converter

General Description

The RT7247A is a high efficiency , monolithic synchronous
step-down DC/DC converter that can deliver up to 2A
output current from a 4.5V to 18V input supply. The
RT7247A's current mode architecture and external
compensation allow the transient response to be
optimized over a wide input range and loads. Cycle-by­cycle current limit provides protection against shorted
outputs, and soft-start eliminate s input current surge during
start-up. The RT7247A also provides under voltage
protection and thermal shutdown protection. The low
current (<3μA) shutdown mode provides output
disconnection, enabling easy power management in
battery-powered systems. The RT7247A is available in
an SOP-8 (Exposed Pad) pa ckage.

Features







±±

±±

±1.5% High Accuracy Reference Voltage





 4.5V to 18V Input Voltage Range





 2A Output Current





 Integrated N-MOSFET Switches





 Current Mode Control





 Fixed Frequency Operation : 340kHz





 Output Adjustable from 0.8V to 15V





 Stable with Low ESR Ceramic Output Capacitors





 Up to 95% Efficiency





 Programmable Soft-Start





 Cycle-by-Cycle Over Current Protection





 Input Under Voltage Lockout





 Output Under Voltage Protection





 Thermal Shutdown Protection





 RoHS Compliant and Halogen Free

Marking Information

RT7247Ax
GSPYMDNN

RT7247AxGSP : Product Number
x : H or L or N
YMDNN : Date Code

Simplified Application Circuit

VIN

EN

GND

BOOT

FB

SW

L

R1

R2

V

OUT

V

IN

RT7247A

SS

C

SS

COMP

C

C

R

C

C

P

C

BOOT

C

IN

C

OUT

Chip Enable

RT7247A

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Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.

Functional Pin Description

Pin No. Pin Name Pin Function

1 BOOT

Bootstrap for High Side Gate Driver. Connect a 0.1F or greater ceramic
capacitor from BOOT to SW pins.

2 VIN

Input Supply Voltage, 4.5V to 18V. Must bypass with a suitable large ceramic
capacitor.

3 SW Switch Node. Connect this pin to an external L-C filter.

4,

9 (Exposed Pad)

GND

Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.

5 FB

Feedback Input. It is used to regulate the output of the converter to a set value
via an external resistive voltage divider.

6 COMP

Compensation Node. COMP is used to compensate the regulation control
loop. Connect a series RC network from COMP to GND. In some cases, an
additional capacitor from COMP to GND is required.

7 EN

Enable Input. A logic high enables the converter; a logic low forces the IC into
shutdown mode reducing the supply current to less than 3A. Attach this pin
to VIN with a 100k pull-up resistor for automatic startup.

8 SS

Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor
from SS to GND to set the soft-start period. A 0.1F capacitor sets the
soft-start period to 13.5ms.

Ordering Information

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.

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

RT7247A

Lead Plating System
G : Green (Halogen Free and Pb Free)

H : UVP Hiccup
L : UVP Latch-Off
N : UVP Disabled

Pin Configurations

(TOP VIEW)

SOP-8 (Exposed Pad)

BOOT

VIN
SW

GND

SS
EN

FB

COMP

GND

2
3
4

5

6

7

8

9

RT7247A

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Function Block Diagram

R

SENSE

+

-

+

-

+

-

UV

Comparator

Oscillator

Foldback

Control

0.4V

Internal

Regulator

+

-

1.8V

Shutdown

Comparator

Current Sense

Amplifier

BOOT

VIN

GND

SW

FB

EN

COMP

VAV

CC

6µA

Slope Comp

Current

Comparator

+

-

EA

0.8V

SRQ

Q

SS

+

-

1.2V

Lockout

Comparator

V

CC

+

150m

5k

V

A

130m

Operation

Shutdown Comparator

Activate internal regulator once EN input level is larger
than the target level. Force IC to enter shutdown mode
when the EN input level is lower tha n 0.4V.

Internal Regulator

Provide internal power for logic control and switch gate
drivers.

Lockout Comparator

Activate the Current Comparator, release lock-out logic,
and enable the switches as EN input level is larger than
lockout voltage. Otherwise, the switches still locks out.

Oscillator

The oscillator provides internal clock and controls the
converter's switching frequency.

Foldback Control

Dyna mically adjust the internal clock. It provides a slower
frequency as a lower FB voltage.

UV Comparator

As FB voltage is lower than the UV voltage, it will a ctivate
a UV protect scheme.

Error Amp

The output voltage COMP of the error a mplifier is adjusted
comparing FB signal with the internal reference voltage
and SS signal.

Current Sense Amplifier

R

SENSE

detects the peak current of the high-side switch.
This signal is amplified by the Current Sense Amplifier
and added with a Slope Compensation. Then, it controls
the switches by comparing this signal with the COMP
voltage.

RT7247A

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Electrical Characteristics

(V

IN

= 12V, TA = 25°C, unless otherwise specified)

Absolute Maximum Ratings (Note 1)

 Supply Input V oltage, V

IN

------------------------------------------------------------------------------------------ −0.3V to 20V

 Switch Voltage, SW ------------------------------------------------------------------------------------------------ −0.3V to (V

IN

+ 0.3V)

<10ns ------------------------------------------------------------------------------------------------------------------ −5V to 25V

 V

BOOT

− VSW---------------------------------------------------------------------------------------------------------- −0.3V to 6V

 Other Pins Voltage ------------------------------------------------------------------------------------------------- −0.3V to 20V
 Power Dissipation, P

D

@ T

A

= 25°C

SOP-8 (Exposed Pad) --------------------------------------------------------------------------------------------- 1.333W

 Package Thermal Re sistance (Note 2)

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

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

HBM (Human Body Model)---------------------------------------------------------------------------------------- 2kV

Recommended Operating Conditions (Note 4)

 Supply Input V oltage, V

IN

------------------------------------------------------------------------------------------ 4.5V to 18V

 Junction T emperature Range-------------------------------------------------------------------------------------- −40°C to 125°C
 Ambient T emperature Range--------------------------------------------------------------------------------------

−40°C to 85°C

Parameter Symbol Test Conditions Min Typ Max Unit

Shutdown Supply Current V

EN

= 0V -- 0.5 3 A

Supply Current V

EN

= 3V, VFB = 0.9V -- 0.8 1.2 mA

Reference Voltage V

REF

4.5V VIN 18V 0.788 0.8 0.812 V

Error Amplifier
Transconductance

G

EA

IC = ±10A -- 940 -- A/V

High Side Switch
On-Resistance

R

DS(ON)1

-- 150 -- m

Low Side Switch
On-Resistance

R

DS(ON)2

-- 130 -- m

High Side Switch Leakage
Current

V

EN

= 0V, VSW = 0V -- 0 10 A

Upper Switch Current Limit Min. Duty Cycle, V

BOOT

VSW = 4.8V -- 4 -- A

COMP to Current Sense
Transconductance

G

CS

-- 3.7 -- A/V

Oscillation Frequency f

OSC1

300 340 380 kHz

Short Circuit Oscillation
Frequency

f

OSC2

VFB = 0V -- 100 -- kHz

Maximum Duty Cycle D

MAX

VFB = 0.7V -- 93 -- %

Minimum On-Time tON -- 100 -- ns

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Parameter Symbol Test Conditions Min Typ Max Unit

Logic-High VIH 2 -- 18

EN Input Voltage

Logic-Low V

IL

-- -- 0.4

V

Input Under Voltage Lockout
Threshold

V

UVLO

VIN Rising 3.8 4.2 4.5 V

Input Under Voltage Lockout
Hysteresis

V

UVLO

-- 320 -- mV

Soft-Start Current ISS V

SS

= 0V -- 6 -- A

Soft-Start Period tSS C

SS

= 0.1F -- 13.5 -- ms

Thermal Shut down TSD -- 150 -- C

Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are

stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in
the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may
affect device reliability.

Note 2. θ

JA

is measured at T

A

= 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is

measured at the exposed pad of the package.

Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.