®
RT5795A
2A, 5.5V, Low I
Q
ACOT Synchronous Step-Down Converter
General Description
The RT5795A is a full featured 5.5V, 2A, Advanced
Constant-On-Time (ACOT) synchronous step-down
converter with two integrated MOSFETs. The advanced
COT operation allows transient responses to be optimized
over a wide range of loads, and output capacitors to
efficiently reduce external component count. The RT5795A
provides up to 2.7MHz switching frequency to minimize
the size of output inductor and capacitors. The RT5795A
is available in the WDFN-8SL 2x2 package.
Features
2.5V to 5.5V Input Voltage Range
Advanced COT Control loop design
Fast Transient Response
Internal 100mΩ and 80mΩ Synchronous Rectifier
Ω
Ω
Highly Accurate V
OUT
Regulation Over Load/Line
Range
Robust Loop Stability with Low-ESR
C
OUT
Ordering Information
RT5795A
Pin 1 Orientation
***
(2) : Quadrant 2, Follow EIA-481-D
Package Type
QW : WDFN-8SL 2x2 (W-Type)
(Exposed Pad-Option 2)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
***Empty means Pin1 orientation is Quadrant 1
Richtek products are :
½
Applications
Mobile Phones and Handheld Devices
STB, Cable Modem, and xDSL Platforms
WLAN ASIC Power / Storage (SSD and HDD)
General Purpose for POL LV Buck Converter
Pin Configurations
(TOP VIEW)
EN
PGND
AGND
FB
1
2
3
4
8
7
6
5
9
VIN
LX
PGOOD
VOS
PGND
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.
WDFN-8SL 2x2
½
Marking Information
2L : Product Code
2LW
W : Date Code
Simplified Application Circuit
RT5795A
V
IN
VIN
EN
LX
PGND
AGND
VOS
FB
R1
V
OUT
PGOOD
Power Good
R2
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS5795A-03 December 2014
www.richtek.com
1
RT5795A
Functional Pin Description
Pin No.
1
Pin Name
EN
Pin Function
Enable Control Input. Pull High to Enable.
Power Ground. The exposed pad must be soldered to a large PCB and
connected to PGND for maximum power dissipation.
Analog Ground. Should be electrically connected to GND close to the device.
Feedback Voltage Input.
Output Voltage Sense Pin for the Internal Control Loop. Must be connected to
output.
Power Good Open-Drain Output. This pin is pulled to low if the output voltage is
below regulation limits. Can be left floating if not used.
Switch Node. The Source of the internal high-side power MOSFET, and Drain of
the internal low-side (synchronous) rectifier MOSFET.
Power Input Supply Voltage, 2.5V to 5.5V.
2,
PGND
9 (Exposed Pad)
3
4
5
6
7
8
AGND
FB
VOS
PGOOD
LX
VIN
Function Block Diagram
EN
VOS
UVLO
OTP
AGND
Shutdown
Control
TON
Comparator
+
-
LX
VIN
FB
Error Amplifier
+
-
+
Logic
Control
Current
Limit
Detector
AZC
Driver
LX
V
REF
PGOOD
Ramp
Generator
LX
V
FB
+
LX
LX
PGND
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
-
is a registered trademark of Richtek Technology Corporation.
DS5795A-03 December 2014
RT5795A
Operation
The RT5795A is a low voltage synchronous step-down
converter that can support input voltage ranging from 2.5V
to 5.5V and the output current can be up to 2A. The
RT5795A uses ACOT
TM
mode control. To achieve good
stability with low-ESR ceramic capacitors, the ACOT uses
a virtual inductor current ramp generated inside the IC.
This internal ramp signal replaces the ESR ramp normally
provided by the output capacitor's ESR. The ramp signal
and other internal compensations are optimized for low-
ESR ceramic output capacitors.
In steady-state operation, the feedback voltage, with the
virtual inductor current ramp added, is compared to the
reference voltage. When the combined signal is less than
the reference, the on-time one-shot is triggered, as long
as the minimum off-time one-shot is clear and the
measured inductor current (through the synchronous
rectifier) is below the current limit. The on-time one-shot
turns on the high-side switch and the inductor current
ramps up linearly. After the on-time, the high-side switch
is turned off and the synchronous rectifier is turned on
and the inductor current ramps down linearly. At the same
time, the minimum off-time one-shot is triggered to prevent
another immediate on-time during the noisy switching
time and allow the feedback voltage and current sense
signals to settle. The minimum off-time is kept short so
that rapidly-repeated on-times can raise the inductor
current quickly when needed.
PWM Frequency and Adaptive On-Time Control
The on-time can be roughly estimated by the equation :
V
1
T
ON
=
OUT
where f
OSC
is nominal 2.7MHz
V
IN
f
OSC
Under-Voltage Protection (UVLO)
The UVLO continuously monitors the VCC voltage to make
sure the device works properly. When the VCC is high
enough to reach the UVLO high threshold voltage, the
step-down converter softly starts or pre-bias to its regulated
output voltage. When the VCC decreases to its low
threshold voltage, the device shuts down.
Power Good
When the output voltage is higher than PGOOD rising
threshold, the PGOOD flag is high.
Output Under-Voltage Protection (UVP)
When the output voltage is lower than 66% reference
voltage after soft-start, the UVP is triggered.
Over-Current Protection (OCP)
The RT5795A senses the current signal when the high-
side and low-side MOSFET turns on. As a result, The
OCP is a cycle-by-cycle current limit. If an over-current
condition occurs, the converter turns off the next on pulse
until inductor current drops below the OCP limit. If the
OCP is continually activated and the load current is larger
than the current provided by the converter, the output
voltage drops. Also, when the output voltage triggers the
UVP also, the current will drop to ZC and trigger the re-
soft start sequence.
Soft-Start
An internal current source charges an internal capacitor
to build the soft-start ramp voltage. The typical soft-start
time is 150μs.
Over-Temperature Protection (OTP)
The RT5795A has an over-temperature protection. When
the device triggers the OTP, the device shuts down until
the temperature is back to normal.
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS5795A-03 December 2014
www.richtek.com
3
RT5795A
Absolute Maximum Ratings
(Note 1)
−0.3V
to 6V
−0.3V
to (V
IN
+ 0.3V)
1.538W
65°C/W
8°C/W
Supply Input Voltage, VIN -----------------------------------------------------------------------------------------
Other Pins -------------------------------------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 25°C
WDFN-8SL 2x2 ------------------------------------------------------------------------------------------------------
Package Thermal Resistance (Note 2)
WDFN-8SL 2x2,
θ
JA
-------------------------------------------------------------------------------------------------
WDFN-8SL 2x2,
θ
JC
------------------------------------------------------------------------------------------------
Junction Temperature ----------------------------------------------------------------------------------------------- 150°C
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------- 260°C
Storage Temperature Range --------------------------------------------------------------------------------------
−65°C
to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------- 2kV
(Note 4)
Recommended Operating Conditions
Supply Input Voltage, VIN -----------------------------------------------------------------------------------------
2.5V to 5.5V
Junction Temperature Range --------------------------------------------------------------------------------------
−40°C
to 125°C
Ambient Temperature Range --------------------------------------------------------------------------------------
−40°C
to 85°C
Electrical Characteristics
(V
IN
= 3.6V, T
A
= 25°C, unless otherwise specified)
Parameter
Under-Voltage Lockout
Threshold
Under-Voltage Lockout
Hysteresis
Shutdown Supply Current
Quiescent Current
Voltage Reference
Current Limit
High-Side
Low-Side
Symbol
V
UVLO
V
UVLOHY
I
SHDN
I
Q
V
REF
I
LIM
V
PGTH
V
PGHY
I
PG
V
PGL
V
ENR
V
ENF
EN = 0V
Test Conditions
V
CC
Rising
Min
2.28
--
--
--
0.441
Typ
2.35
400
--
30
0.45
3.2
2.4
10
5
0.01
--
--
--
Max
2.48
--
1
--
0.459
4
2.9
5
--
0.1
0.3
--
0.4
Unit
V
mV
A
A
V
A
%
%
A
V
V
V
Active, V
FB
= 0.5V, No Switching
Peak Current
Valley Current
V
OUT
Falling Referenced to V
OUT
Nominal
Hysteresis Referenced to V
OUT
Nominal
V
PG
= 5V
I
sink
= 500A
Rising
Falling
2.5
2
15
--
--
--
1
--
Power Good Threshold
Power Good Hysteresis
Power Good Leakage
Current
Power Good Low Level
Voltage
Enable Rising Threshold
Enable Falling Threshold
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS5795A-03 December 2014
RT5795A
Parameter
Switch
On-Resistance
High-Side
Low-Side
Symbol
R
P-MOSFET
R
N-MOSFET
Test Conditions
Min
--
--
--
--
f
OSC
--
--
Typ
100
80
150
20
2.7
1
Max
--
--
--
--
--
--
Unit
m
C
C
MHz
k
Thermal Shutdown
Temperature
Thermal Shutdown
Hysteresis
Switching Frequency
Output Discharge Resistor
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.
θ
JC
is
measured at the exposed pad of the package. The copper area is 70mm
2
connected with IC exposed pad.
Note 3.
Devices are ESD sensitive. Handling precaution is recommended.
Note 4.
The device is not guaranteed to function outside its operating conditions.
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS5795A-03 December 2014
www.richtek.com
5
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
