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PDF RT6236A Data sheet ( Hoja de datos )
| Número de pieza | RT6236A | |
| Descripción | Synchronous Step-Down Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT6236A/B
6A, 18V, 650kHz, ACOTTM Synchronous Step-Down Converter
General Description
The RT6236A/B is a high-performance 650kHz, 6A 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 RT6236A/B is stable with and optimized
for ceramic output capacitors. With internal 51mΩ switches
and 18mΩ synchronous rectifiers, the RT6236A/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
lock-out, externally-adjustable soft-start, output under- and
over-voltage protection, and thermal shutdown provide safe
and smooth operation in all operating conditions. The
RT6236A/B is available in the UQFN-13JL 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
6A Output Current
51mΩ Internal High-Side N-MOSFET and 18mΩ
Internal Low-Side N-MOSFET
Steady 650kHz 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
Externally-Adjustable, Pre-Biased Compatible Soft-
Start
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
CIN
VPVCC
RPG
Enable
CSS
RT6236A/B
VIN SW
BOOT
PGOOD
EN FB
SS PVCC
GND
L
CBOOT
CFF R1
COUT
VOUT
VPVCC
CPVCC
R2
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
DS6236A/B-01 December 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
“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
650kHz switching and encouraging the circuit to remain
in continuous conduction, preventing repetitive mode
transitions between continuous switching and
discontinuous switching.
Current Limit
The RT6236A/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 Over-Voltage Protection and Under-Voltage
Protection
If the output voltage VOUT rises above the regulation level
and lower 1.2 times regulation level, the high-side switch
naturally remains off and the synchronous rectifier turns
on. For RT6236B, if the output voltage remains high the
synchronous rectifier remains on until the inductor current
reaches the low side current limit. If the output voltage
still remains high, then IC's switches remain that the
synchronous rectifier turns on and high-side MOS keeps
off to operate at typical 500kHz switching protection, again
if inductor current reaches low side current, the
synchronous rectifier will turn off until next protection
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
DS6236A/B-01 December 2015
RT6236A/B
clock. If the output voltage exceeds the OVP trip threshold
(1.25 times regulation level) for longer than 10μs (typical),
then IC's output Over-Voltage Protection (OVP) is
triggered. RT6236BL chip enters latch mode.
For RT6236A If the output voltage Vo rises above the
regulation level and lower 1.2 times regulation level, the
high-side switch naturally remains off and the synchronous
rectifier turns on until the inductor current reaches zero
current. If the output voltage remains high, then IC's
switches remain off. If the output voltage exceeds the OVP
trip threshold (1.25 times regulation level) for longer than
10μs (typical), the IC's OVP is triggered. RT6236AL chip
enters latch mode.
The RT6236A/B include output Under-Voltage Protection
(UVP). If the output voltage drops below the UVP trip
threshold for longer than 250μs (typical) then IC's UVP is
triggered. Chip into latch or hiccup mode. (see next
section).
Hiccup Mode
The RT6236AH/BH, use hiccup mode for UVP. When the
protection function is triggered, the IC will shut down for a
period of time and then attempt to recover automatically.
Hiccup mode allows the circuit to operate safely with low
input current and power dissipation, and then resume
normal operation as soon as UVP is removed. During
hiccup mode, the shutdown time is determined by the
capacitor at SS. A 2μA current source discharges VSS
from its starting voltage (normally VPVCC). The IC remains
shut down until VSS reaches 0.2V, about 10ms for a 3.9nF
capacitor. At that point the IC begins to charge the SS
capacitor at 6μA, and a normal start-up occurs. If the fault
remains, UVP protection will be enabled when VSS reaches
2.2V (typical). The IC will then shut down and discharge
the SS capacitor from the 2.2V level, taking about 4ms for
a 3.9nF SS capacitor.
Latch-Off Mode
The RT6236AL/BL, use latch-off mode OVP and UVP.
When the protection function is triggered the IC will shut
down in Latch-Off Mode. The IC stops switching, leaving
both switches open, and is latched off. To restart operation,
toggle EN or power the IC off and then on again.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
RT6236A/B
Switching Frequency vs. Output Current
800
700 RT6236A
600 RT6236B
500
400
300
200
100
0
0123456
Output Current (A)
Feedback Voltage vs. Input Voltage
0.73
0.72
0.71
0.70
0.69
0.68
0.67
0.66
4 6 8 10 12 14 16 18
Input Voltage (V)
Inductor Valley Current Limit vs. Input Voltage
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4 6 8 10 12 14 16 18
Input Voltage (V)
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
DS6236A/B-01 December 2015
Switching Frequency vs. Temperature
850
800
750
700
650
600
550
500
450
-50
-25
IOUT = 1A
0 25 50 75
Temperature (°C)
100 125
Feedback Voltage vs. Temperature
0.73
0.72
0.71
0.70
0.69
0.68
0.67
0.66
-50
-25
0 25 50 75 100 125
Temperature (°C)
Inductor Valley Current Limit vs. Temperature
8.0
7.5
7.0
6.5
6.0
5.5
5.0
-50
-25
0 25 50 75
Temperature (°C)
100 125
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet RT6236A.PDF ] | |
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