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PDF RT6239A Data sheet ( Hoja de datos )
| Número de pieza | RT6239A | |
| Descripción | Synchronous Step-Down Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT6239A/B
9A, 18V, 500kHz, ACOTTM Synchronous Step-Down Converter
General Description
The RT6239A/B is a high-performance 500kHz, 9A step-
down regulator with internal power switches and
synchronous rectifiers. It features quick transient response
using its Advanced Constant On-Time (ACOTTM) control
architecture that provides stable operation with small
ceramic output capacitors and without complicated
external compensation, among other benefits. The input
voltage range is from 4.5V to 18V and the output is
adjustable from 0.7V to 8V. The proprietary ACOTTM control
improves upon other fast response constant on-time
architectures, achieving nearly constant switching
frequency over line, load, and output voltage ranges. Since
there is no internal clock, response to transients is nearly
instantaneous and inductor current can ramp quickly to
maintain output regulation without large bulk output
capacitance. The RT6239A/B is stable with and optimized
for ceramic output capacitors. With internal 30mΩ switches
and 12mΩ synchronous rectifiers, the RT6239A/B displays
excellent efficiency and good behavior across a range of
applications, especially for low output voltages and low
duty cycles. Cycle-by-cycle current limit provides
protection against shorted outputs, input under-voltage
lockout, externally-adjustable soft-start, output under- and
over-voltage protection, and thermal shutdown provide safe
and smooth operation in all operating conditions. The
RT6239A/B is available in the UQFN-14L 2x3 (FC)
package, with exposed thermal pad.
Features
Fast Transient Response
Advanced Constant On-Time (ACOTTM) Control
4.5V to 18V Input Voltage Range
Adjustable Output Voltage from 0.7V to 8V
9A Output Current
30mΩ Internal High-Side N-MOSFET and 12mΩ
Internal Low-Side N-MOSFET
Steady 500kHz Switching Frequency
Up to 95% Efficiency
Optimized for All Ceramic Capacitors
Externally-Adjustable, Pre-Biased Compatible Soft-
Start
Cycle-by-Cycle Current Limit
Input Under-Voltage Lockout
Output Over- and Under-Voltage Protection
Power Good Output
Thermal Shutdown
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
Simplified Application Circuit
VIN
EN Signal
Power Good
RT6239A/B
VIN SW
BOOT
EN FB
PGOOD
PVCC
SS
GND
VOUT
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
DS6239A/B-04 May 2016
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
cause the effective input voltage to be less than the
measured input voltage and the effective output voltage to
be greater than the measured output voltage. As the load
changes, the switch voltage drops change causing a
switching frequency variation with load current. Also, at
light loads if the inductor current goes negative, the switch
dead-time between the synchronous rectifier turn-off and
the high-side switch turn-on allows the switching node to
rise to the input voltage. This increases the effective on
time and causes the switching frequency to drop
noticeably.
One way to reduce these effects is to measure the actual
switching frequency and compare it to the desired range.
This has the added benefit eliminating the need to sense
the actual output voltage, potentially saving one pin
connection. ACOTTM uses this method, measuring the
actual switching frequency and modifying the on-time with
a feedback loop to keep the average switching frequency
in the desired range.
To achieve good stability with low-ESR ceramic capacitors,
ACOTTM uses a virtual inductor current ramp generated
inside the IC. This internal ramp signal replaces the ESR
ramp normally provided by the output capacitor's ESR.
The ramp signal and other internal compensations are
optimized for low-ESR ceramic output capacitors.
ACOTTM One-Shot Operation
The RT6239A/B control algorithm is simple to understand.
The feedback voltage, with the virtual inductor current ramp
added, is compared to the reference voltage. When the
combined signal is less than the reference and the on-
time one-shot is triggered, as long as the minimum off-
time one-shot is clear and the measured inductor current
(through the synchronous rectifier) is below the current
limit. The on-time one-shot turns on the high-side switch
and the inductor current ramps up linearly. After the on
time, the high-side switch is turned off and the synchronous
rectifier is turned on and the inductor current ramps down
linearly. At the same time, the minimum off-time one-shot
is triggered to prevent another immediate on-time during
the noisy switching time and allow the feedback voltage
and current sense signals to settle. The minimum off-time
is kept short (230ns typical) so that rapidly-repeated on-
RT6239A/B
times can raise the inductor current quickly when needed.
Discontinuous Operating Mode (RT6239A Only)
After soft-start, the RT6239A operates in fixed frequency
mode to minimize interference and noise problems. The
RT6239A uses variable-frequency discontinuous switching
at light loads to improve efficiency. During discontinuous
switching, the on-time is immediately increased to add
“hysteresis” to discourage the IC from switching back to
continuous switching unless the load increases
substantially.
The IC returns to continuous switching as soon as an on-
time is generated before the inductor current reaches zero.
The on-time is reduced back to the length needed for
500kHz switching and encouraging the circuit to remain
in continuous conduction, preventing repetitive mode
transitions between continuous switching and
discontinuous switching.
Current Limit
The RT6239A/B current limit is a cycle-by-cycle “valley”
type, measuring the inductor current through the
synchronous rectifier during the off-time while the inductor
current ramps down. The current is determined by
measuring the voltage between Source and Drain of the
synchronous rectifier. If the inductor current exceeds the
current limit, the on-time one-shot is inhibited (Mask high
side signal) until the inductor current ramps down below
the current limit. Thus, only when the inductor current is
well below the current limit is another on time permitted.
This arrangement prevents the average output current from
greatly exceeding the guaranteed current limit value, as
typically occurs with other valley-type current limits. If
the output current exceeds the available inductor current
(controlled by the current limit mechanism), the output
voltage will drop. If it drops below the output under-voltage
protection level the IC will stop switching (see next section).
Output Under-Voltage Protection
Hiccup Mode
The RT6239AH/RT6239BH provide Hiccup Mode Under-
Voltage Protection (UVP). When the FB voltage drops
below 60% of the feedback reference voltage, the output
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
DS6239A/B-04 May 2016
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
Typical Operating Characteristics
98
94
90
86
82
78
74
70
0
Efficiency vs. Output Current
VOUT = 1V
VOUT = 1.1V
VOUT = 1.2V
VOUT = 1.5V
VOUT = 1.8V
VOUT = 3.3V
VOUT = 5V
RT6239A : PSM, VIN = 12V, fSW = 500kHz
123456789
Output Current (A)
Efficiency vs. Output Current
98
94
90 VOUT = 1V
VOUT = 1.1V
86 VOUT = 1.2V
VOUT = 1.5V
82 VOUT = 1.8V
VOUT = 3.3V
78
74
RT6239A : PSM, VIN = 5V, fSW = 500kHz
70
0123456789
Output Current (A)
Output Voltage vs. Input Voltage
1.10
RT6239A
1.09
1.08
1.07
1.06
1.05
1.04
IOUT = 0A
IOUT = 3A
IOUT = 6A
IOUT = 9A
1.03
1.02
VOUT = 1V
4 6 8 10 12 14 16 18
Input Voltage (V)
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
DS6239A/B-04 May 2016
RT6239A/B
98
94
90
86
82
78
74
70
0
Efficiency vs. Output Current
VOUT = 1V
VOUT = 1.1V
VOUT = 1.2V
VOUT = 1.5V
VOUT = 1.8V
VOUT = 3.3V
VOUT = 5V
RT6239B : PWM, VIN = 12V, fSW = 500kHz
123456789
Output Current (A)
98
94
90
86
82
78
74
70
0
Efficiency vs. Output Current
VOUT = 1V
VOUT = 1.1V
VOUT = 1.2V
VOUT = 1.5V
VOUT = 1.8V
VOUT = 3.3V
RT6239B : PWM, VIN = 5V, fSW = 500kHz
123456789
Output Current (A)
Output Voltage vs. Input Voltage
1.10
RT6239B
1.09
1.08
1.07
1.06
1.05
1.04
1.03
1.02
IOUT = 0A
IOUT = 3A
IOUT = 6A
IOUT = 9A
VOUT = 1V
4 6 8 10 12 14 16 18
Input Voltage (V)
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet RT6239A.PDF ] | |
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