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PDF DS6550A Data sheet ( Hoja de datos )
| Número de pieza | DS6550A | |
| Descripción | Synchronous DC-DC Step-Down Controller | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT6550A
Synchronous DC-DC Step-Down Controller with 5V LDO
General Description
The RT6550A is a step-down, controller generating supply
voltages for battery-powered systems. It includes Pulse-
Width Modulation (PWM) controller adjustable from 2V
to 5.5V, and a 5V linear regulator which provides up to
100mA output current. Other features include on-board
power-up sequencing, internal soft-start, and soft-
discharge output that prevents negative voltage during
shutdown.
A constant current ripple PWM control scheme operates
without sense resistors and provides 100ns response to
load transient. The RT6550A is available in the WDFN-
10L 3x3 package.
Ordering Information
RT6550A
Pin 1 Orientation***
(2) : Quadrant 2, Follow EIA-481-D
Package Type
QW : WDFN-10L 3x3 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
***Empty means Pin1 orientation is Quadrant 1
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.
Features
Support Connected Shutdown Mode for Ultrabook
CCRCOT Control with 100ns Load Step Response
PWM Maximum Duty Ratio > 98%
5V to 25V Input Voltage Range
2V to 5.5V Output Voltage Range
5V LDO with 100mA Output Current
Internal Frequency Setting with 300kHz @ VIN =12V
Internal Soft-Start and Soft-Discharge
4700ppm/°C RDS(ON) Current Sensing
Independent Switcher Enable Control
Built-In OVP/UVP/OCP/OTP
Non-Latch UVLO
Applications
Notebook and Sub-Notebook Computers
System Power Supplies
3-Cell and 4-Cell Li+ Battery-Powered Devices
Pin Configuration
(TOP VIEW)
EN 1
CS 2
FB 3
VO_DIS 4
LDO5 5
10 LGATE
9 PHASE
8 UGATE
7 BOOT
11 6 VIN
WDFN-10L 3x3
Marking Information
6W= : Product Code
6W=YM
DNN
YMDNN : Date Code
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
DS6550A-00 September 2016
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
RT6550A
Electrical Characteristics
(VIN = 12V, VEN = 3.3V, VCS = 2V, No Load, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Input Supply
VIN Power On Reset
VIN_POR
Rising Threshold
Falling Threshold
VIN Shutdown Supply
Current
VIN Quiescent Current
IVIN_SBY
IVIN
Buck Controller Off, VEN = GND
UGATE / LGATE Floating,
VIN = 12V, No Switching
Buck Controllers Output and FB Voltage
FB Valley Trip Voltage
VO_DIS Discharge
Current
PHASE Discharge
Current
VFB
IDCHG
IDCHG_LX
CCM Operation
VVO_DIS = 0.5V
VPHASE = 0.5V
Switching Frequency
Switching Frequency
Minimum Off-Time
fSW
tOFF(MIN)
VIN = 12V, VOUT = 5V
VFB = 1.9V
Soft-Start
Soft-Start Time
tSS VOUT Ramp-up Time
Current Sense
CS Source Current
CS Current Temperature
Coefficient
ICS
TCICS
VCS = 1V
In Comparison with 25°C
Internal Regulator
LDO5 Output Voltage
VLDO5
LDO5 Output Current
ILDO5
VIN = 12V, No Load
VIN > 7V, ILDO5 < 100mA
VIN > 5.5V, ILDO5 < 35mA
VIN > 5V, ILDO5 < 20mA
VLDO5 = 4.5V, VIN = 7.4V
UVLO
LDO5 UVLO Threshold
VUVLO5
Rising Edge
Falling Edge
Fault Detection
OVP Trip Threshold
OVP Propagation Delay
UVP Trip Threshold
UVP Shutdown Blanking
Time
VOVP
VUVP
tSHDN_UVP
FB with Respect to Internal Reference
UVP Detect, FB Falling Edge
From EN Enable
Min
--
3.2
--
--
1.98
10
5
240
--
--
9
--
4.9
4.8
4.8
4.5
100
--
3.7
109
--
47
--
Typ
4.6
3.7
20
420
2
45
8
300
200
0.9
10
4700
5
5
5
4.75
175
4.3
3.9
113
1
52
1.3
Max Unit
4.9
V
--
35 A
750 A
2.02 V
-- mA
-- mA
360 kHz
275 ns
-- ms
11 A
-- ppm/C
5.1
5.1
V
5.1
5.1
-- mA
4.6
V
4.1
117 %
-- s
57 %
-- ms
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
DS6550A-00 September 2016
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
PHASE is above the current limit threshold, the PWM is
not allowed to initiate a new cycle (Figure 2). The actual
peak current is greater than the current limit threshold by
an amount equal to the inductor ripple current. Therefore,
the exact current limit characteristic and maximum load
capability are a function of the sense resistance, inductor
value, battery and output voltage.
IL
IPEAK
ILOAD
ILIMIT
t
Figure 2. “Valley” Current Limit
The RT6550A uses the on resistance of the synchronous
rectifier as the current sense element and supports
temperature compensated MOSFET RDS(ON) sensing. The
RILIM resistor between the CS pin and GND sets the current
limit threshold. The resistor RILIM is connected to a current
source from CS which is 10μA (typ.) at room temperature.
The current source has a 4700ppm/°C temperature slope
to compensate the temperature dependency of the
RDS(ON). When the voltage drop across the sense resistor
or low-side MOSFET equals 1/8 the voltage across the
RILIM resistor, positive current limit will be activated. The
high-side MOSFET will not be turned on until the voltage
drop across the MOSFET falls below 1/8 the voltage across
the RILIM resistor.
Choose a current limit resistor according to the following
equation :
VLIMIT = (RLIMIT x 10μA) / 8 = ILIMIT x RDS(ON)
RLIMIT = (ILIMIT x RDS(ON)) x 8 / 10μA
Carefully observe the PC board layout guidelines to ensure
that noise and DC errors do not corrupt the current sense
signal at PHASE and GND. Mount or place the IC close
to the low-side MOSFET.
RT6550A
MOSFET Gate Driver (UGATE, LGATE)
The high-side driver is designed to drive high current, low
RDS(ON) N-MOSFET(s). When configured as a floating driver,
5V bias voltage is delivered from the LDO5 supply. The
average drive current is also calculated by the gate charge
at VGS = 5V times switching frequency. The instantaneous
drive current is supplied by the flying capacitor between
the BOOT and PHASE pins. A dead-time to prevent shoot
through is internally generated from high-side MOSFET
off to low-side MOSFET on and low-side MOSFET off to
high-side MOSFET on.
The low-side driver is designed to drive high current low
RDS(ON) N-MOSFET(s). The internal pull down transistor
that drives LGATE low is robust, with a 1Ω typical on-
resistance. A 5V bias voltage is delivered from the LDO5
supply. The instantaneous drive current is supplied by an
input capacitor connected between LDO5 and GND.
For high current applications, some combinations of high
and low-side MOSFETs may cause excessive gate drain
coupling, which leads to efficiency killing, EMI producing,
and shoot through currents. This is often remedied by
adding a resistor in series with BOOT, which increases
the turn-on time of the high-side MOSFET without
degrading the turn-off time. See Figure 3.
VIN
UGATE
BOOT
RBOOT
PHASE
Figure 3. Increasing the UGATE Rise Time
Soft-Start
The RT6550A provides an internal soft-start function to
prevent large inrush current and output voltage overshoot
when the converter starts up. The soft-start (SS)
automatically begins once the chip is enabled. During soft-
start, it clamps the ramping of internal reference voltage
which is compared with FB signal. The typical soft-start
duration is 0.9ms. An unique PWM duty limit control that
prevents output over-voltage during soft-start period is
designed specifically for FB floating.
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
DS6550A-00 September 2016
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet DS6550A.PDF ] | |
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