RT7296C
3A, 17V Current Mode Synchronous Step-Down Converter
General Description
The RT7296C is a high-efficiency, 3A current mode
synchronous step-down DC/DC converter with a wide
input voltage range from 4.5V to 17V. The device
integrates 80m
high-side
and
30m
low-side
Features
4.5V to 17V Input Voltage Range
3A Output Current
Internal N-Channel MOSFETs
Current Mode Control
Fixed Switching Frequency : 1.4MHz
Synchronous to External Clock : 300kHz to 3MHz
Cycle-by-Cycle Current Limit
External Soft-Start Function
Input Under-Voltage Lockout
Output Under-Voltage Protection
Thermal Shutdown
MOSFETs to achieve high efficiency conversion. The
current
mode control
architecture supports fast
transient response and internal compensation. A
cycle-by-cycle current limit function provides protection
against
complete
shorted output.
protection
The
RT7296C provides
such
as
input
functions
under-voltage lockout, output under-voltage protection,
over-current protection, and thermal shutdown. The
PWM frequency is adjustable by the EN/SYNC pin. The
RT7296C is available in the TSOT-23-8 (FC) package.
Applications
Industrial and Commercial Low Power Systems
Computer Peripherals
LCD Monitors and TVs
Set-top Boxes
Ordering Information
RT7296C
Package Type
J8F : TSOT-23-8 (FC)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
RoHS compliant and compatible with the current
requirements of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
00=DNN
00= : Product Code
DNN : Date Code
Simplified Application Circuit
RT7296C
BOOT
VIN
C1
SW
Enable
EN/SYNC
R5
PVCC
C2
SS
C5
GND
FB
R2
C4
R1
C3
L1
V
OUT
V
IN
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7296C-02
June 2016
www.richtek.com
1
RT7296C
Pin Configurations
(TOP VIEW)
EN/SYNC
6
3
8
7
2
VIN
SW
SS
TSOT-23-8 (FC)
Functional Pin Description
Pin No.
1
2
3
4
5
Pin Name
SS
VIN
SW
GND
BOOT
Pin Function
Soft-Start Control Input. SS control the soft-start period. Connect a capacitor
from SS to GND to set the soft-start period.
Power Input. Support 4.5V to17V Input Voltage. Must bypass with a suitable
large ceramic capacitor at this pin.
Switch Node. Connect to external L-C filter.
System Ground.
Bootstrap Supply for High-Side Gate Driver. Connect a 0.1F ceramic
capacitor between the BOOT and SW pins.
Enable Control Input. High = Enable. Apply an external clock to adjust the
switching frequency. If using pull high resistor connected to VIN, the
recommended value range is 60k to 300k.
5V Bias Supply Output. Connect a minimum of 0.1F capacitor to ground.
Feedback Voltage Input. The pin is used to set the output voltage of the
converter to regulate to the desired voltage via a resistive divider. Feedback
reference = 0.8V.
6
7
8
EN/SYNC
PVCC
FB
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
GND
is a registered trademark of Richtek Technology Corporation.
BOOT
5
4
PVCC
FB
DS7296C-02
June 2016
RT7296C
Function Block Diagram
PVCC
VIN
EN/SYNC
1.4V
Shutdown
- Comparator
+
Internal
Regulator
UVLO
BOOT
UVLO
Current
Sense
BOOT
0.4V
+
-
UV
Comparator
1pF
50pF
FB
0.807V
400k
-
+ EA
+
Oscillator
HS Switch
Current
Comparator
Slope
Compensation
LS Switch
Current
Comparator
Current
Sense
Logic &
Protection
Control
Power
Stage &
Deadtime
Control
SW
GND
11µA
SS
Operation
Under Voltage Lockout Threshold
The IC includes an input Under Voltage Lockout
Protection (UVLO). If the input voltage exceeds the
UVLO rising threshold voltage (3.9V), the converter
resets and prepares the PWM for operation. If the input
voltage falls below the UVLO falling threshold voltage
(3.25V) during normal operation, the device stops
switching. The UVLO rising and falling threshold
voltage includes a hysteresis to prevent noise caused
reset.
Chip Enable
The EN pin is the chip enable input. Pulling the EN pin
low (<1.1V) will shutdown the device. During shutdown
mode, the RT7296C’s quiescent current drops to lower
than 1A. Driving the EN pin high (>1.6V) will turn on
the device.
Operating Frequency and Synchronization
The internal oscillator runs at 1400kHz (typ.) when the
EN/SYNC pin is at logic-high level (>1.6V). If the EN
pin is pulled to low-level over 8μs, the IC will shut
down. The RT7296C can be synchronized with an
external clock ranging from 300kHz to 3MHz applied to
the EN/SYNC pin. The external clock duty cycle must
be from 20% to 80% with logic-high level = 2V and
logic-low level = 0.8V.
Internal Regulator
The internal regulator generates 5V power and drive
internal circuit. When VIN is below 5V, PVCC will drop
with VIN. A capacitor (>0.1F) between PVCC and
GND is required.
Soft-Start Function
The RT7296C provides external soft-start function. The
soft-start function is used to prevent large inrush
current while converter is being powered-up. The
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7296C-02
June 2016
www.richtek.com
3
RT7296C
soft-start timing can be programmed by the external
capacitor between SS pin and GND. The Chip provides
a 11A charge current for the external capacitor.
Over Current Protection
RT7296C provides cycle-by-cycle over current limit
protection. When the inductor current peak value
reaches current limit, IC will turn off High Side MOS to
avoid over current.
Under Voltage Protection (Hiccup Mode)
RT7296C provides Hiccup Mode of Under Voltage
Protection (UVP). When the FB voltage drops below
half of the feedback reference voltage, V
FB
, the UVP
function will be triggered and the IC will shut down for a
period of time and then recover automatically. The
Hiccup Mode of UVP can reduce input current in
short-circuit conditions.
Thermal Shutdown
Thermal shutdown is implemented to prevent the chip
from operating at excessively high temperatures. When
the junction temperature is higher than 150C, the chip
will shutdown the switching operation. The chip is
automatically
re-enabled
when
the
junction
temperature cools down by approximately 20C.
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS7296C-02
June 2016
RT7296C
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage, VIN
-----------------------------------------------------------------------------------
0.3V
to 20V
Switch Voltage, SW
--------------------------------------------------------------------------------------------
0.3V
to V
IN
+ 0.3V
<20ns
---------------------------------------------------------------------------------------------------------------
5V
BOOT to SW, V
BOOT – SW
-----------------------------------------------------------------------------------
0.3V
to 6V (7V for < 10s)
Bias Supply Output, PVCC----------------------------------------------------------------------------------
0.3V
to 6V (7V for < 10s)
Other Pins---------------------------------------------------------------------------------------------------------
0.3V
to 6V
Power Dissipation, P
D
@ T
A
= 25C
TSOT-23-8 (FC)
------------------------------------------------------------------------------------------------
1.428W
Package Thermal Resistance
(Note 2)
TSOT-23-8 (FC),
JA
-----------------------------------------------------------------------------------------
70C/W
TSOT-23-8 (FC),
JC
-----------------------------------------------------------------------------------------
15C/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, VIN --------------------------------------------------------------------------------------- 4.5V to 17V
Junction Temperature Range
----------------------------------------------------------------------------------------
40C
to 125C
Ambient Temperature Range
----------------------------------------------------------------------------------------
40C
to 85C
Electrical Characteristics
(V
IN
= 12V, T
A
= 25C, unless otherwise specified)
Parameter
Shutdown Supply Current
Quiescent Current with no Load
at DCDC Output
Feedback Voltage
Feedback Current
Switch
On-Resistance
Switch Leakage
Current Limit
Low-Side Switch Current Limit
Oscillation Frequency
SYNC Frequency Range
Fold-Back Frequency
Maximum Duty-Cycle
DS7296C-02
June 2016
Symbol
Test Conditions
V
EN
= 0V
V
EN
= 2V, V
FB
= 1V
Min
--
--
0.799
Typ
--
0.8
0.807
10
80
30
--
5
2
1400
--
125
85
Max
1
1
0.815
50
--
--
1
--
--
1700
3000
--
--
Unit
A
mA
V
nA
m
A
A
A
kHz
kHz
kHz
%
V
FB
I
FB
High-Side
Low-Side
R
DS(ON)H
R
DS(ON)L
V
EN
= 0V, V
SW
= 0V
I
LIM
Under 40% duty-cycle
From Drain to Source
f
OSC
f
SYNC
V
FB
< 400mV
D
MAX
V
FB
= 0.7V
V
FB
= 0.75V
V
FB
= 820mV
--
--
--
--
4.2
--
1100
300
--
--
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
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