RT5796A
1.5A, 1MHz, 6V CMCOT Synchronous Step-Down Converter
General Description
The RT5796A is a high efficiency synchronous
step-down DC/DC converter. Its input voltage range is
from 2.5V to 6V and provides an adjustable regulated
output voltage from 0.6V to 3.4V while delivering up to
1.5A of output current.
The internal synchronous low on-resistance power
switches increase efficiency and eliminate the need for
an external Schottky diode. The Current Mode
Constant-On-time (CMCOT) operation with internal
compensation allows the transient response to be
optimized over a wide range of loads and output
capacitors. The RT5796A is available in the
T/SOT-23-5 and T/SOT-23-6 packages.
Features
Efficiency Up to 95%
R
DSON
160m HS / 110m LS
V
IN
Range 2.5V to 6V
V
REF
0.6V with
2%
Accuracy
CMCOT
™
Control Loop Design for Best
Transient Response, Robust Loop Stability with
Low-ESR (MLCC) C
OUT
Fixed Soft-Start 1.2ms; PGOOD Function in
T/SOT-23-6
Cycle-by-Cycle Over Current Protection
Input Under Voltage Lockout
Output Under Voltage Protection (UVP Hiccup)
Thermal Shutdown Protection
Power Saving at Light Load
Ordering Information
RT5796A
Package Type
B : SOT-23-5
E : SOT-23-6
J5 : TSOT-23-5
J6 : TSOT-23-6
Lead Plating System
G : Green (Halogen Free and Pb Free)
UVP Trim Option
H: Hiccup
PWM/PSM Mode
A : PSM/PWM
Note :
Richtek products are :
Applications
STB, Cable Modem, & xDSL Platforms
LCD TV Power Supply & Metering Platforms
General Purpose Point of Load (POL)
Pin Configurations
(TOP VIEW)
FB
5
VIN
4
FB
6
PG VIN
5
4
2
3
2
3
EN GND LX
EN GND LX
T/SOT-23-5
T/SOT-23-6
RoHS compliant and compatible with the current
requirements of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
Simplified Application Circuit
V
IN
C
IN
RT5796A
LX
VIN
EN
PG*
GND
FB
R2
L
V
OUT
R1
C
OUT
*For T/SOT-23-6 Package Only
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS5796A-03
October
2015
www.richtek.com
1
RT5796A
Marking Information
RT5796AHGB
RT5796AHGE
58= : Product Code
DNN : Date Code
21= : Product Code
DNN : Date Code
58=DNN
RT5796AHGJ5
21=DNN
RT5796AHGJ6
09=DNN
09= : Product Code
DNN : Date Code
0V=DNN
0V= : Product Code
DNN : Date Code
Functional Pin Description
Pin No.
T/SOT-23-5
1
2
3
T/SOT-23-6
1
2
3
Pin Name
EN
GND
LX
Enable Control Input.
Power Ground and Quiet Ground for Controller Circuits.
Switch Node.
Supply Voltage Input. The RT5796A operates from a 2.5V to 6V
unregulated input. C1 is needed to prevent large voltage spikes from
appearing at the input.
Quiet ground for controller circuits.
Feedback Voltage Input. An external resistor divider from the output to
GND, tapped to the FB pin, sets the output voltage.
Power Good Indicator. The output of this pin is an open-drain with
external pull-up resistor to IN. PG is pulled up to IN when the FB voltage
is within 90%, otherwise it is LOW.
Pin Function
4
4
VIN
5
6
FB
--
5
PG
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS5796A-03
October
2015
RT5796A
Function Block Diagram
For T/SOT-23-5 Package
EN
VIN
UVLO
OTP
FB
V
REF
Shut Down
Control
Error
Amplifier
R
C
C
COMP
Comparator
+
-
Ton
LX
VIN
-
+
Logic
Control
Current
Limit
Detector
Current
Sense
Driver
LX
GND
LX
For T/SOT-23-6 Package
EN
VIN
UVLO
OTP
FB
V
REF
-
+
Shut Down
Control
Error
Amplifier
R
C
C
COMP
Comparator
+
-
Ton
LX
VIN
Logic
Control
Current
Limit
Detector
Current
Sense
Driver
LX
GND
+
-
LX
PG
Operation
The RT5796A is a synchronous low voltage step-down
converter that can support the input voltage range from
2.5V to 6V and the output current can be up to 1.5A.
The RT5796A uses a constant on-time, current mode
architecture. In normal operation, the high side
P-MOSFET is turned on when the switch controller is
set by the comparator and is turned off when the Ton
comparator resets the switch controller.
Low side MOSFET peak current is measured by
internal RSENSE. The error amplifier EA adjusts COMP
voltage by comparing the feedback signal (V
FB
) from
the output voltage with the internal 0.6V reference.
When the load current increases, it causes a drop in the
feedback voltage relative to the reference, then the
COMP voltage rises to allow higher inductor current to
match the load current.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS5796A-03
October
2015
www.richtek.com
3
RT5796A
UV Comparator
If the feedback voltage (V
FB
) is lower than threshold
voltage 0.2V, the UV comparator's output will go high
and the switch controller will turn off the high side
MOSFET. The output under voltage protection is
designed to operate in Hiccup mode.
PGOOD Comparator
When the feedback voltage (V
FB
) is higher than
threshold voltage 0.54V, the PGOOD open drain output
will be high impedance. The internal PG MOSFET is
typical 100. The PGOOD signal delay time from EN is
about 2ms.
Enable Comparator
A logic-high enables the converter; a logic-low forces
the IC into shutdown mode.
Soft-Start (SS)
An internal current source charges an internal capacitor
to build the soft-start ramp voltage. The V
FB
voltage will
track the internal ramp voltage during soft-start interval.
The typical soft-start time is 1.2ms.
Over Current Protection (OCP)
The RT5796A provides over current protection by
detecting low side MOSFET valley inductor current. If
the sensed valley inductor current is over the current
limit threshold (1.8A typ.), the OCP will be triggered.
When OCP is tripped, the RT5796A will keep the over
current threshold level until the over current condition is
removed.
Thermal Shutdown (OTP)
The device implements an internal thermal shutdown
function when the junction temperature exceeds 150°C.
The thermal shutdown forces the device to stop
switching when the junction temperature exceeds the
thermal shutdown threshold. Once the die temperature
decreases below the hysteresis of 20°C, the device
reinstates the power up sequence.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS5796A-03
October
2015
RT5796A
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage -----------------------------------------------------------------------------------------
0.3V
to 6.5V
LX Pin Switch Voltage----------------------------------------------------------------------------------------
0.3V
to (V
IN
+ 0.3V)
<20ns -------------------------------------------------------------------------------------------------------------
4.5V
to 7.5V
Power Dissipation, P
D
@ T
A
= 25C
T/SOT-23-5 -----------------------------------------------------------------------------------------------------
0.43W
T/SOT-23-6 -----------------------------------------------------------------------------------------------------
0.5W
Package Thermal Resistance
(Note 2)
T/SOT-23-5,
JA
-----------------------------------------------------------------------------------------------
230.6C/W
T/SOT-23-6,
JA
-----------------------------------------------------------------------------------------------
197.4C/W
T/SOT-23-5,
JC
-----------------------------------------------------------------------------------------------
21.8C/W
T/SOT-23-6,
JC
-----------------------------------------------------------------------------------------------
18.9C/W
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------
260C
Junction Temperature ----------------------------------------------------------------------------------------
40C
to 150C
Storage Temperature Range -------------------------------------------------------------------------------
65C
to 150C
ESD Susceptibility
(Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------
2kV
Recommended Operating Conditions
(Note 4)
Supply Input Voltage -----------------------------------------------------------------------------------------
2.5V
to 6V
Ambient Temperature Range-------------------------------------------------------------------------------
40C
to 85C
Junction Temperature Range ------------------------------------------------------------------------------
40C
to 125C
Electrical Characteristics
(V
IN
= 3.6V, T
A
= 25C, unless otherwise specified)
Parameter
Input Voltage
Feedback Reference Voltage
Feedback Leakage Current
DC Bias Current
Switching Leakage Current
Switching Frequency
Switch On Resistance, High
Switch On Resistance, Low
Valley Current Limit
Under-Voltage Lockout Threshold
Symbol
V
IN
V
REF
I
FB
Test Conditions
Min
2.5
0.588
Typ
--
0.6
--
22
--
--
1
160
110
1.8
2.25
2
Max
6
0.612
1
--
1
1
--
--
--
2.4
2.5
--
Unit
V
V
A
A
A
MHz
m
m
A
V
V
V
FB
= 3.3V
Active , V
FB
= 0.63V,
Not Switching
Shutdown
--
--
--
--
--
R
PMOS
R
NMOS
I
LIM
V
UVLO
I
SW
= 0.3A
I
SW
= 0.3A
--
--
1.53
VDD Rising
VDD Falling
--
--
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS5796A-03
October
2015
www.richtek.com
5
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