Richtek RT7266ZSP Schematic [ru]
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®
RT7266
3A, 18V, 700kHz ACOTTM Synchronous Step-Down
Converter
General Description
The RT7266 is an adaptive on-time ACOTTM mode synchronous buck converter. The adaptive on-timeACOTTM mode control provides a very fast transient response with few external components. The low impedance internal MOSFET can support high efficiency operation with wide input voltage range from 4.5V to 18V . The proprietary circuit of the RT7266 enables to support all ceramic capacitors. The output voltage can be adjustable between 0.8V and 8V. The soft-start is adjustable by an external capacitor.
Ordering Information
RT7266 
Package Type
SP : SOP-8 (Exposed Pad-Option 2)
Lead Plating System
Z : ECO (Ecological Element with 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.
Features
zACOTTM Mode Enables Fast Transient Response
z4.5V to 18V Input Voltage Range
z3A Output Current
z60mΩ Internal Low Site N-MOSFET
zAdaptive On-Time Control
zFast Transient Response
zSupport All Ceramic Capacitors
zUp to 95% Efficiency
z700kHz Switching Frequency
zAdjustable Output Voltage from 0.8V to 8V
zAdjustable Soft-Start
zCycle-by-Cycle Current Limit
zInput Under Voltage Lockout
zThermal Shutdown Protection
zRoHS Compliant and Halogen Free
Applications
zIndustrial and Commercial Low Power Systems
zComputer Peripherals
zLCD Monitors and TVs
zGreen Electronics/Appliances
zPoint of Load Regulation for High-Performance DSPs, FPGAs, and ASICs
Marking Information |
Pin Configurations |
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RT7266 |
RT7266ZSP : Product Number |
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(TOP VIEW) |
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YMDNN : Date Code |
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ZSPYMDNN |
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EN |
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8 |
VIN |
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FB |
2 |
7 |
BOOT |
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PVCC |
GND |
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SW |
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3 |
6 |
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SS |
9 |
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GND |
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4 |
5 |
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SOP-8 (Exposed Pad)
Copyright ©2012 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS7266-02 September 2012 |
www.richtek.com |
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1 |
RT7266
Typical Application Circuit
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L1 |
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8 |
RT7266 |
6 |
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1.4µH |
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VOUT |
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VIN |
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VIN |
SW |
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1.05V/3A |
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C1 |
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C2 |
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C6 |
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C7 |
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10µF x 2 |
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0.1µF |
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7 |
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0.1µF |
C3 |
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R1 |
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22µF x 2 |
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8.25k |
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Chip |
Enable |
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1 |
EN |
BOOT |
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2 |
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5, 9 (Exposed Pad) |
GND |
FB |
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3 |
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R2 |
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4 |
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SS |
PVCC |
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VPVCC |
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22.1k |
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C5 |
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C4 |
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3.9nF |
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1µF |
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Table 1. Suggested Component Values
VOUT (V) |
R1 (kΩ) |
R2 (kΩ) |
C3 (pF) |
L1 (μH) |
C7 (μF) |
1 |
6.81 |
22.1 |
-- |
1.4 |
22 to 68 |
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1.05 |
8.25 |
22.1 |
-- |
1.4 |
22 to 68 |
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1.2 |
12.7 |
22.1 |
-- |
1.4 |
22 to 68 |
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1.8 |
30.1 |
22.1 |
5 to 22 |
2 |
22 to 68 |
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2.5 |
49.9 |
22.1 |
5 to 22 |
2 |
22 to 68 |
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3.3 |
73.2 |
22.1 |
5 to 22 |
2 |
22 to 68 |
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5 |
124 |
22.1 |
5 to 22 |
3.3 |
22 to 68 |
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7 |
180 |
22.1 |
5 to 22 |
3.3 |
22 to 68 |
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Functional Pin Description
Pin No. |
Pin Name |
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Pin Function |
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Enable Input. A logic-high enables the converter; a logic-low forces the RT7266 |
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1 |
EN |
into shutdown mode reducing the supply current to less than 10μA. Attach this |
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pin to VIN with a 100kΩ pull up resistor for automatic start-up. |
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Feedback Input. It is used to regulate the output of the converter to a set value |
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2 |
FB |
via an external resistive voltage divider. The feedback reference voltage is |
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0.765V typically. |
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3 |
PVCC |
Internal Regulator |
Output. Connect a 1μF capacitor to GND to stabilize |
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output voltage. |
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Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor |
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4 |
SS |
from SS to GND to set the soft-start period. A 3.9nF capacitor sets the soft-start |
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period to 1.5ms. |
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5, 9 (Exposed pad) |
GND |
Ground. The Exposed pad should be soldered to a large PCB and connected to |
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GND for maximum thermal dissipation. |
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6 |
SW |
Switch Node. Connect this pin to an external L-C filter. |
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7 |
BOOT |
Bootstrap for High Side Gate Driver. Connect a 0.1μF or |
greater ceramic |
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capacitor from BOOT to SW pins. |
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8 |
VIN |
Supply Input. The input voltage range is from 4.5V to 18V. Must bypass with a |
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suitable large ( ≥10μF x 2) ceramic capacitor. |
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Copyright ©2012 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
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www.richtek.com |
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DS7266-02 |
September 2012 |
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2 |
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RT7266
Function Block Diagram
VIN |
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PVCC |
Reg |
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BOOT |
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UGATE |
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OC |
Control |
Driver |
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SW |
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LGATE |
GND |
SS |
Soft-Start |
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FB |
On-Time |
+ |
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EN |
EN |
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- |
Comparator |
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VREF |
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Copyright ©2012 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS7266-02 September 2012 |
www.richtek.com |
3
RT7266
Absolute Maximum Ratings |
(Note 1) |
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z Supply Voltage, VIN ----------------------------------------------------------------------------------------------- |
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−0.3V to 20V |
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z Switch Voltage, SW ----------------------------------------------------------------------------------------------- |
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−0.8V to (VIN + 0.3V) |
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< 10ns----------------------------------------------------------------------------------------------------------------- |
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−5V to 25V |
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z BOOT to SW -------------------------------------------------------------------------------------------------------- |
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−0.3V to 6V |
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z All Other Pins ------------------------------------------------------------------------------------------------------- |
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−0.3V to 6V |
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z Power Dissipation, PD @ TA = 25°C |
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SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------------- |
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1.333W |
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z Package Thermal Resistance |
(Note 2) |
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SOP-8 (Exposed Pad), θJA --------------------------------------------------------------------------------------- |
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75°C/W |
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SOP-8 (Exposed Pad), θJC -------------------------------------------------------------------------------------- |
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15°C/W |
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z Junction Temperature Range ------------------------------------------------------------------------------------- |
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150°C |
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z Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------ |
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260°C |
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z Storage Temperature Range ------------------------------------------------------------------------------------- |
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−65°C to 150°C |
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Recommended Operating Conditions |
(Note 3) |
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z Supply Voltage, VIN ----------------------------------------------------------------------------------------------- |
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4.5V to 18V |
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z Junction Temperature Range ------------------------------------------------------------------------------------- |
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−40°C to 125°C |
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z Ambient Temperature Range ------------------------------------------------------------------------------------- |
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−40°C to 85°C |
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Electrical Characteristics |
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(VIN = 12V, TA = 25°C, unless otherwise specified) |
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Parameter |
Symbol |
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Test Conditions |
Min |
Typ |
Max |
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Unit |
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Supply Current |
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Shutdown Current |
ISHDN |
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VEN = 0V |
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-- |
1 |
10 |
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μA |
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Quiescent Current |
IQ |
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VEN = 3V, VFB = 1V |
-- |
0.7 |
-- |
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mA |
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Logic Threshold |
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EN Voltage |
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Logic-High |
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2 |
-- |
5.5 |
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V |
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Logic-Low |
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-- |
-- |
0.4 |
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VREF Voltage and Discharge Resistance |
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Feedback Reference Voltage |
VREF |
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4.5V ≤ VIN ≤ 18V |
0.753 |
0.765 |
0.777 |
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V |
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Feedback Input Current |
IFB |
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VFB = 0.8V |
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−0.1 |
0 |
0.1 |
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μA |
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VPVCC Output |
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VPVCC Output Voltage |
VPVCC |
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6V ≤ VIN ≤ 18V, 0 < IPVCC < 5mA |
4.7 |
5.1 |
5.5 |
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V |
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Line Regulation |
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6V ≤ VIN ≤ 18V, IPVCC = 5mA |
-- |
-- |
20 |
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mV |
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Load Regulation |
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0 < IPVCC < 5mA |
-- |
-- |
60 |
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mV |
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Output Current |
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IPVCC |
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VIN = 6V, VPVCC = 4V |
-- |
110 |
-- |
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mA |
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RDS(ON) |
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Switch On |
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High Side |
RDS(ON)_H |
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-- |
90 |
-- |
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mΩ |
Resistance |
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Low Side |
RDS(ON)_L |
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-- |
60 |
-- |
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Current Limit |
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Current limit |
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ILIM |
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3.5 |
4.1 |
5.7 |
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A |
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Copyright ©2012 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
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www.richtek.com |
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DS7266-02 |
September 2012 |
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4 |
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RT7266
Parameter |
Symbol |
Test Conditions |
Min |
Typ |
Max |
Unit |
Thermal Shutdown |
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Thermal Shutdown Threshold |
TSD |
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-- |
150 |
-- |
°C |
Thermal Shutdown |
TSD |
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-- |
20 |
-- |
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Hysteresis |
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On-Time Timer Control |
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On-Time |
tON |
VIN = 12V, VOUT = 1.05V |
-- |
145 |
-- |
ns |
Minimum On-Time |
tON(MIN) |
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-- |
60 |
-- |
ns |
Minimum Off-Time |
tOFF(MIN) |
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-- |
230 |
-- |
ns |
Soft-Start |
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SS Charge Current |
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VSS = 0V |
1.4 |
2 |
2.6 |
μA |
SS Discharge Current |
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VSS = 0.5V |
0.05 |
0.1 |
-- |
mA |
UVLO |
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UVLO Threshold |
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VIN Rising to Wake up VPVCC |
3.55 |
3.85 |
4.15 |
V |
Hysteresis |
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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. θJA is measured at TA = 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. The device is not guaranteed to function outside its operating conditions.
Copyright ©2012 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS7266-02 September 2012 |
www.richtek.com |
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