|
|
PDF DS6257B Data sheet ( Hoja de datos )
| Número de pieza | DS6257B | |
| Descripción | Step-Down Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de DS6257B (archivo pdf) en la parte inferior de esta página. Total 15 Páginas | ||
|
No Preview Available !
®
RT6257A/B
6A, 18V, 500kHz, ACOTTM Step-Down Converter
General Description
Features
The RT6257A/B is a high-efficiency, monolithic 4.5V to 18V Input Voltage Range
synchronous step-down DC-DC converter that can deliver 6A Output Current
up to 6A output current from a 4.5V to 18V input supply. Constant-On-Time Mode to Enables Fast Transient
The RT6257A/B adopts ACOT architecture to allow the
Response
transient response to be improved and keep in constant Low Output Ripple and Allows Ceramic Output
frequency. Cycle-by-cycle current limit provides protection
Capacitor
against shorted outputs and soft-start eliminates input 500kHz Switching Frequency
current surge during start-up. Fault conditions also include High Efficient Internal Power MOSFET Switch
output under voltage protection and thermal shutdown.
Optimized for Lower Duty Cycle Applications
Integrated 30mΩ/20mΩ MOSFETs
Ordering Information
RT6257A/B
Adjustable Output Voltage from 0.6V to 5V
Internal Soft-Start (1.5ms typ.)
Package Type
J6F : TSOT-23-6 (FC)
Built-In UVP/OTP
Input Under Voltage Lockout
TSOT23-6 (FC) Package
Lead Plating System
G : Green (Halogen Free and Pb Free)
UVP Option
H : Hiccup
Applications
Set Top Box
PSM/PWM
A : PSM/PWM
B : Force-PWM
Portable TV
Access Point Router
DSL Modem
Note :
LCD TV
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 Configuration
(TOP VIEW)
BOOT LX VIN
Marking Information
RT6257AHGJ6F
2K=DNN
2K= : Product Code
DNN : Date Code
654
23
FB EN GND
TSOT-23-6 (FC)
RT6257BHGJ6F
2J=DNN
2J= : Product Code
DNN : Date Code
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
DS6257A/B-00 September 2016
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
RT6257A/B
Absolute Maximum Ratings (Note 1)
Supply Input Voltage and EN Voltage, VIN, EN ---------------------------------------------------------------- −0.3V to 20V
Switch Voltage, LX ---------------------------------------------------------------------------------------------------- −0.3V to 20V
<20ns -------------------------------------------------------------------------------------------------------------------- −5V to 27V
BOOT to LX, VBOOT − VLX ------------------------------------------------------------------------------------------------------------------------------------ −0.3V to 6V
Other Pins --------------------------------------------------------------------------------------------------------------- −0.3V to 6V
Power Dissipation, PD @ TA = 25°C
TSOT-23-6 (FC) --------------------------------------------------------------------------------------------------------- 2.12W
Package Thermal Resistance (Note 2)
TSOT-23-6 (FC), θJA --------------------------------------------------------------------------------------------------- 47°C/W
TSOT-23-6 (FC), θJC --------------------------------------------------------------------------------------------------- 2°C/W
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
Recommended Operating Conditions (Note 4)
Supply Input Voltage -------------------------------------------------------------------------------------------------- 4.5V to 18V
Junction Temperature Range ---------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range ---------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 12V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Conditions
Min Typ Max Unit
Supply Voltage
VIN Supply Input Operating
Voltage
VIN
4.5 -- 18 V
VIN Under-Voltage Lockout
Threshold-Rising
VUVLO
VIN rising
3.9 4.1 4.3 V
VIN Under-Voltage Lockout
Threshold-Hysteresis
VUVLO
-- 0.3 --
V
Supply Current
Supply Current (Shutdown)
Supply Current (Quiescent)
ISHDN
IQ
VEN = 0
IOUT = 0
VFB = VREF x 105%, not switching
--
--
3 --
115 --
A
A
Soft-Start
Soft-Start Time
tSS
-- 1.5 -- ms
Enable Voltage
EN Input High Voltage
EN Input Low Voltage
VEN_H
VEN_L
1.5 -- -- V
-- -- 0.4 V
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
DS6257A/B-00 September 2016
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
RT6257A/B
Output Ripple Voltage
Output ripple voltage at the switching frequency is caused
by the inductor current ripple and its effect on the output
capacitor's ESR and stored charge. These two ripple
components are called ESR ripple and capacitive ripple.
Since ceramic capacitors have extremely low ESR and
relatively little capacitance, both components are similar
in amplitude and both should be considered if ripple is
critical.
VRIPPLE = VRIPPLE(ESR) VRIPPLE(C)
VRIPPLE(ESR) = IL RESR
VRIPPLE(C)
=
IL
8 COUT fSW
The typical operating circuit design for the RT6257A/B,
the output voltage is 5V, inductor ripple current is 1.77A,
and using 2 pieces of 22μF output capacitor with about
5mΩ ESR, the output voltage ripple components are :
VRIPPLE(ESR) = IL RESR = 1.77A 5m = 8.85mV
VRIPPLE(C)
=
IL
8 COUT fSW
=
1.77A
8 44μF 500kHz
= 10mV
VRIPPLE = VRIPPLE(ESR) VRIPPLE(C) = 18.85mV
Output Transient Undershoot and Overshoot
In addition to output ripple voltage at the switching
frequency, the output capacitor and its ESR also affect
the voltage sag (undershoot) and soar (overshoot) when
the load steps up and down abruptly. The ACOT transient
response is very quick and output transients are usually
small. However, the combination of small ceramic output
capacitors (with little capacitance), low output voltages
(with little stored charge in the output capacitors), and
low duty cycle applications (which require high inductance
to get reasonable ripple currents with high input voltages)
increases the size of voltage variations in response to
very quick load changes. Typically, load changes occur
slowly with respect to the IC's 500kHz switching frequency.
But some modern digital loads can exhibit nearly
instantaneous load changes and the following section
shows how to calculate the worst-case voltage swings in
response to very fast load steps.
The output voltage transient undershoot and overshoot each
have two components : the voltage steps caused by the
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
DS6257A/B-00 September 2016
output capacitor's ESR, and the voltage sag and soar due
to the finite output capacitance and the inductor current
slew rate. Use the following formulas to check if the ESR
is low enough (typically not a problem with ceramic
capacitors) and the output capacitance is large enough to
prevent excessive sag and soar on very fast load step
edges, with the chosen inductor value.
The amplitude of the ESR step up or down is a function of
the load step and the ESR of the output capacitor :
VESR_STEP = IOUT RESR
The amplitude of the capacitive sag is a function of the
load step, the output capacitor value, the inductor value,
the input-to-output voltage differential, and the maximum
duty cycle. The maximum duty cycle during a fast transient
is a function of the on-time and the minimum off-time since
the ACOTTM control scheme will ramp the current using
on-times spaced apart with minimum off-times, which is
as fast as allowed. Calculate the approximate on-time
(neglecting parasitics) and maximum duty cycle for a given
input and output voltage as :
tON
=
VOUT
VIN fSW
and DMAX
=
tON
tON tOFF(MIN)
The actual on-time will be slightly longer as the IC
compensates for voltage drops in the circuit, but we can
neglect both of these since the on-time increase
compensates for the voltage losses. Calculate the output
voltage sag as :
VSAG
=
2 COUT
L (IOUT )2
VIN(MIN) DMAX VOUT
The amplitude of the capacitive soar is a function of the
load step, the output capacitor value, the inductor value
and the output voltage :
VSOAR
=
L (IOUT )2
2 COUT VOUT
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet DS6257B.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| DS6257A | Step-Down Converter | Richtek |
| DS6257B | Step-Down Converter | Richtek |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |