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PDF RT7294A Data sheet ( Hoja de datos )
| Número de pieza | RT7294A | |
| Descripción | SynchronousStep-Down Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT7294A
2.5A, 18V, 500kHz ACOTTMSynchronous Step-Down Converter
General Description
The RT7294A is a synchronous step-down converter with
Advanced Constant On-Time (ACOTTM) mode control. The
ACOTTM provides a very fast transient response with few
external components. The low impedance internal
MOSFET supports high efficiency operation with wide input
voltage range from 4.3V to 18V. The proprietary circuit of
the RT7294A enables to support all ceramic capacitors.
The output voltage can be adjusted between 0.6V and 8V.
Ordering Information
RT7294A
Package Type
J6F : TSOT-23-6 (FC)
Note :
Lead Plating System
G : Green (Halogen Free and Pb Free)
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.
Pin Configurations
(TOP VIEW)
SW VIN EN
654
23
BOOT GND FB
TSOT-23-6 (FC)
Features
4.3V to 18V Input Voltage Range
2.5A Output Current
Advanced Constant On-Time Control
Fast Transient Response
Support All Ceramic Capacitors
Up to 95% Efficiency
500kHz Switching Frequency
Adjustable Output Voltage from 0.6V to 8V
Cycle-by-Cycle Current Limit
Input Under-Voltage Lockout
Hiccup Mode Under-Voltage Protection
Thermal Shutdown
Power Saving Mode for High Efficiency at Light
Load
RoHS Compliant and Halogen Free
Applications
Industrial and Commercial Low Power Systems
Computer Peripherals
LCD Monitors and TVs
Green Electronics/Appliances
Point of Load Regulation for High-Performance DSPs,
FPGAs, and ASICs
Marking Information
01= : Product Code
01=DNN
DNN : Date Code
Simplified Application Circuit
RT7294A
VIN VIN BOOT
SW
Enable
EN FB
GND
VOUT
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS7294A-02 October 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
Typical Application Circuit
RT7294A
VIN
4.3V to 18V
Enable
1C0INµF
RT7294A
5 VIN
BOOT 1
SW 6
4 EN
FB 3
GND 2
CBOOT
100nF
L
2µH
CFF
R1
10k
R2
10k
VOUT
1.2V
COUT
22µF
VOUT (V)
5
3.3
2.5
1.2
Table 1. Suggested Component Values
R1 (k)
110
R2 (k)
15
L (H)
4.7
COUT (F)
22
115 25.5 3.6
22
25.5 8.06
3.6
22
10 10 2 22
CFF (pF)
39
33
NC
NC
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS7294A-02 October 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
RT7294A
Feed-forward Capacitor (Cff)
The RT7294A is optimized for ceramic output capacitors
and for low duty cycle applications. However for high-output
voltages, with high feedback attenuation, the circuit's
response becomes over-damped and transient response
can be slowed. In high-output voltage circuits (VOUT > 3.3V)
transient response is improved by adding a small “feed-
forward” capacitor (Cff) across the upper FB divider resistor
(figure 1), to increase the circuit's Q and reduce damping
to speed up the transient response without affecting the
steady-state stability of the circuit. Choose a suitable
capacitor value that following below step.
Get the BW the quickest method to do transient
response form no load to full load. Confirm the damping
frequency. The damping frequency is BW.
BW
VOUT
FB
RT7294A
GND
R1 Cff
R2
Figure 1. Cff Capacitor Setting
Cff can be calculated base on below equation :
Cff
1
2 3.1412R1BW 0.8
Internal Soft-Start (SS)
The RT7294A soft-start uses an internal soft-start time
800μs.
Following below equation to get the minimum capacitance
range in order to avoid UV occur.
T
COUT VOUT 0.6 1.2
(ILIM Load Current) 0.8
T 800μs
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS7294A-02 October 2014
Enable Operation (EN)
For automatic start-up the EN pin can be connected to
VIN, through a 100kΩ resistor. Its large hysteresis band
makes EN useful for simple delay and timing circuits. EN
can be externally pulled to VIN by adding a resistor-
capacitor delay (REN and CEN in Figure 2). Calculate the
delay time using EN's internal threshold where switching
operation begins (1.4V, typical).
An external MOSFET can be added to implement digital
control of EN when no system voltage above 2V is available
(Figure 3). In this case, a 100kΩ pull-up resistor, REN, is
connected between VIN and the EN pin. MOSFET Q1 will
be under logic control to pull down the EN pin. To prevent
enabling circuit when VIN is smaller than the VOUT target
value or some other desired voltage level, a resistive voltage
divider can be placed between the input voltage and ground
and connected to EN to create an additional input under
voltage lockout threshold (Figure 4).
EN
REN
VIN
CEN
EN
RT7294A
GND
Figure 2. External Timing Control
REN
VIN 100k
Enable
EN
Q1 RT7294A
GND
Figure 3. Digital Enable Control Circuit
VIN REN1
REN2
EN
RT7294A
GND
Figure 4. Resistor Divider for Lockout Threshold Setting
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet RT7294A.PDF ] | |
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