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PDF RT8237D Data sheet ( Hoja de datos )
| Número de pieza | RT8237D | |
| Descripción | (RT8237C/D) High Efficiency Single Synchronous Buck PWM Controller | |
| Fabricantes | RICHTEK | |
| Logotipo |  |
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®
RT8237C/D
High Efficiency Single Synchronous Buck PWM Controller
General Description
The RT8237C/D PWM controller provides high efficiency,
excellent transient response, and high DC output accuracy
needed for stepping down high voltage batteries to
generate low voltage CPU core, I/O, and chipset RAM
supplies in notebook computers.
The constant on-time PWM control scheme handles wide
input/output voltage ratios with ease and provides 100ns
“instant-on” response to load transients while maintaining
a relatively constant switching frequency.
The RT8237C/D achieves high efficiency at a reduced cost
by eliminating the current sense resistor found in
traditional current mode PWMs. Efficiency is further
enhanced by its ability to drive very large synchronous
rectifier MOSFETs and enter diode emulation mode at
light load condition. The buck conversion allows this device
to directly step down high voltage batteries at the highest
possible efficiency. The pre-set frequency selections
minimize design effort required for new designs. The
RT8237C/D is intended for CPU core, chipset, DRAM, or
other low voltage supplies as low as 0.7V. The RT8237C
is available in a WDFN-10L 3x3 package, The RT8237D is
available in a WQFN-12L 2x2 package.
Ordering Information
RT8237 - (2)
Pin 1 Orientation
(2) : Quadrant 2, Follow EIA-481-D
Package Type
QW : WDFN-10L 3x3 (W-Type)
QW : WQFN-12L 2x2 (W-Type)
Lead Plating System
Z : ECO (Ecological Element with
Halogen Free and Pb free)
Note :
C : WDFN-10L 3x3
D : WQFN-12L 2x2
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.
Copyright ©2013 Richtek Technology Corporation. All rights reserved.
DS8237C/D-05 October 2013
Features
z Wide Input Voltage Range : 4.5V to 26V
z Output Voltage Range : 0.7V to 3.3V
z Built-in 0.5% 0.7V Reference Voltage
z Quick Load-Step Response within 100ns
z 4700ppm/°C Programmable Current Limit by Low
Side RDS(ON) Sensing
z 4 Selectable Frequency Setting
z Soft-Start Control
z Drives Large Synchronous-Rectifier FETs
z Integrated Boot Switch
z Built-in OVP/OCP/UVP
z Thermal Shutdown
z Power Good Indicator
z RoHS Compliant and Halogen Free
Applications
z Notebook Computers
z CPU Core Supply
z Chipset/RAM Supply as Low as 0.7V
z Generic DC/DC Power Regulator
Pin Configurations
(TOP VIEW)
PGOOD 1
CS 2
EN 3
FB 4
RF 5
10 BOOT
9 UGATE
8 PHASE
7 VCC
11 6 LGATE
WDFN-10L 3x3
RT8237C
12 11 10
LGATE 1
VCC 2
PHASE 3
GND
13
9 FB
8 EN
7 CS
456
WQFN-12L 2x2
RT8237D
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
Free Datasheet http://www.datasheet4u.com/
1 page  
RT8237C/D
Parameter
VOUT Voltage Range
Switching Frequency
Minimum Off-Time
Current Sensing
CS Source Current
CS Source Current TC
Zero Crossing Threshold
Current Limit Threshold
Negative Current Limit
Threshold
Protection Function
Output UV Threshold
OVP Threshold
OV Fault Delay
VCC Under Voltage Lockout
Threshold
VOUT Soft-Start
UV Blank Time
Thermal Shutdown
Driver On Resistance
UGATE Drive Source
UGATE Drive Sink
LGATE Drive Source
LGATE Drive Sink
Dead Time
Internal Boost Charging Switch
On Resistance
EN Threshold
EN Input
Logic-High
Threshold Voltage Logic-Low
Symbol
fSW
ICS
VLIMIT
UVLO
TSD
RUGATEsr
RUGATEsk
RLGATEsr
RLGATEsk
VIH
VIL
Test Conditions
RRF = 470kΩ
RRF = 200kΩ
RRF = 100kΩ
RRF = 39kΩ
(Note 6)
(Note 6)
(Note 6)
(Note 6)
DEM
GND − PHASE, VCS = 2.4V
GND − PHASE, VCS = 1.6V
GND − PHASE, VCS = 0.4V
PHASE − GND, VCS = 2.4V
PHASE − GND, VCS = 1.6V
PHASE − GND, VCS = 0.4V
With respect to error
comparator threshold
With respect to error
comparator threshold
FB forced above OV threshold
Falling edge,
hysteresis = 100mV, PW M
disabled below this level
From EN = high to VOUT = 95%
From EN signal going high
BOOT − PHASE forced to 5V
BOOT − PHASE forced to 5V
LGATE, High State
LGATE, Low State
LGATE Rising (VPHASE = 1.5V)
UGATE Rising
VCC to BOOT, 10mA
Min
0.7
--
--
--
--
250
9
--
−10
280
185
40
--
--
--
65
120
--
3.7
--
--
--
--
--
--
--
--
--
--
1.8
--
Typ Max
-- 3.3
290 --
340 --
380 --
430 --
400 550
Unit
V
kHz
ns
10
4700
--
300
200
50
300
200
50
11 μA
-- ppm/°C
5 mV
320
215 mV
60
--
-- mV
--
70 75
125 130
5 --
3.9 4.1
1300
3
150
--
--
--
%
%
μs
V
μs
ms
°C
1.8 3.6
1.2 2.4
1.8 3.6
0.8 1.6
30 --
30 --
-- 80
Ω
Ω
Ω
Ω
ns
Ω
-- --
-- 0.5
V
Copyright ©2013 Richtek Technology Corporation. All rights reserved.
DS8237C/D-05 October 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
Free Datasheet http://www.datasheet4u.com/
5 Page 
RT8237C/D
zero current, which is the boundary between continuous
conduction and discontinuous conduction modes. By
emulating the behavior of diodes, the low side MOSFET
allows only partial negative current to flow when the
inductor freewheeling current reaches negative. As the load
current is further decreased, it takes longer and longer to
discharge the output capacitor to the level that requires
the next “ON” cycle. The on-time is kept the same as
that in heavy load condition. On the contrary, when the
output current increases from light load to heavy load, the
switching frequency increases to the preset value as the
inductor current reaches the continuous condition. This
is shown in Figure 1. The transition load point to the light
load operation is calculated as follows :
ILOAD
≈
( VIN
− VOUT
2L
)
× tON
where tON is the on-time.
IL
Slope = (VIN -VOUT) / L
IL, PEAK
ILOAD = IL, PEAK / 2
0 tON
t
Figure 1. Boundary Condition of CCM/DCM
The switching waveforms may appear noisy and
asynchronous when light loading causes diode-emulation
operation, but this is a normal operating condition that
results in high light load efficiency. Trade-offs in DEM noise
vs. light load efficiency is made by varying the inductor
value. Generally, low inductor values produce a broader
efficiency vs. load curve, while higher values result in higher
full load efficiency (assuming that the coil resistance
remains fixed) and less output voltage ripple. The
disadvantages for using higher inductor values include
larger physical size and degraded load transient response
(especially at low input voltage levels).
Forced-CCM Mode (FCCM)
The low noise, forced-CCM mode disables the zero-
crossing comparator, which controls the low side switch
on-time. This causes the low side gate drive waveform to
Copyright ©2013 Richtek Technology Corporation. All rights reserved.
DS8237C/D-05 October 2013
become the complement of the high side gate drive
waveform. This in turn causes the inductor current to
reverse at light loads as the PWM loop to maintain duty
ratio VOUT/VIN. A fairly constant switching frequency is
the benefit of forced-CCM mode, but this comes at a cost.
The no load battery current can be up to 10mA to 40mA,
depending on the external MOSFETs.
Current Limit Setting (CS)
The RT8237C/D has a cycle-by-cycle current limiting
control. The current limit circuit employs a unique “valley”
current sensing algorithm. If the magnitude of the current
sense signal at PHASE is above the current limit
threshold, the PWM is not allowed to initiate a new cycle
(see Figure 2). In order to provide both good accuracy and
a cost effective solution, the RT8237C/D supports
temperature compensated MOSFET RDS(ON) sensing.
The CS pin of the RT8237C/D is a multiplexed pin for
PWM enable/disable control and current limit threshold
setting. Connect a setting resistor from this pin to GND
via an N-MOSFET. When the N-MOSFET is turned off, the
PWM is disabled. When the N-MOSFET is turned on, the
PWM is enabled and the current limit threshold is equal
to 1/8 of the voltage at this pin.
Choose a current limit resistor by following below equation:
ROC_SET
=
VCS_OC
ICS
=
⎛⎜⎝ILOAD_OC
− IRIPPLE
2
ICS
⎞
⎟⎠
×
8
×
RDS(ON)
Inductor current is monitored by the voltage between the
GND pin and the PHASE pin, so the PHASE pin should
be connected to the drain terminal of the low side
MOSFET. ICS has a temperature coefficient to compensate
the temperature dependency of the RDS(ON). GND is used
as the positive current sensing node, so GND should be
connected to the source terminal of the low side MOSFET.
As the comparison is being done during the OFF state,
VLIMIT (current limit threshold) sets the valley level of the
inductor current. Thus, the load current at over current
threshold, ILOAD_OC, can be calculated as follows :
ILOAD_OC
=
VCS_OC
8 × RDS(ON)
+
IRIPPLE
2
= VCS_OC + 1 × (VIN − VOUT )× VOUT
8 ×RDS(ON) 2 ×L × f
VIN
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
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Datas
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet RT8237D.PDF ] | |
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