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PDF MAX1917 Data sheet ( Hoja de datos )
| Número de pieza | MAX1917 | |
| Descripción | Tracking / Sinking and Sourcing / Synchronous Buck Controller for DDR Memory and Termination Supplies | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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19-2335; Rev 1; 6/02
Tracking, Sinking and Sourcing, Synchronous Buck
Controller for DDR Memory and Termination Supplies
General Description
The MAX1917 provides a complete power-manage-
ment solution for DDR memory. It contains a synchro-
nous buck controller and an amplifier to generate
1/2VDDR voltage for VTT and VTTR. The VTT and VTTR
voltages are maintained within 1% of 1/2VDDR. The
controller operates in synchronous rectification mode to
ensure balanced current sourcing and sinking capabili-
ty of up to 25A. With a shutdown current of less than
5µA, the MAX1917 is the best choice for low-power
notebook applications, as well as servers and desktop
computers. An all N-FET design optimizes efficiency.
The MAX1917 can also be used for generating VDDR
and as a general-purpose step-down controller with
variable switching frequency as high as 1MHz with few
additional components.
The MAX1917 uses Maxim’s proprietary Quick-PWM™
architecture for fast transient response up to 96% effi-
ciency, and the smallest external components. Output
current monitoring is achieved without sense resistors
by monitoring the bottom FET’s drain-to-source voltage.
The current-limit threshold is programmable through an
external resistor. The MAX1917 comes in a space-sav-
ing 16-pin QSOP package.
Applications
DDR Memory Power
Supply
Processor or DSP Core
Supply
AGTL Bus Termination
Supply
Notebook Computers
Desktop Computers
Storage
Networking Systems
Quick-PWM is a trademark of Maxim Integrated Products, Inc.
TOP VIEW
Pin Configuration
EN/HSD 1
DDR 2
POK 3
VTT 4
ILIM 5
FSEL 6
REF 7
GND 8
MAX1917EEE
16 LX
15 DH
14 BST
13 PGND
12 DL
11 VL
10 V+
9 VTTR
QSOP
Features
o 25A Sourcing and Sinking Current
o Automatically Sets VTT to 1/2VDDR
o VTT and VTTR Within 1% of 1/2VDDR
o Smallest Output Capacitors
o 4.5V to 14V (or 28V with Resistor-Divider) Input
Voltage Range
o 1.5V to 3.6V Input DDR Range
o 200kHz/300kHz/400kHz/550kHz Preset Switching
Frequencies
o Variable Switching Frequency of Up to 1MHz
o Overcurrent Protection Without Current-Sense
Resistor
o Internal Soft-Start
o VTTR Reference Sources and Sinks Up to 25mA
o Quick-PWM Control for Fastest Loop Response
o Up to 96% Efficiency
o 16-Pin QSOP Package
PART
MAX1917EEE
Ordering Information
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
16 QSOP
VIN (2.5V TO 15V)
Typical Operating Circuit
POK
VDDR
(4.5V TO 14V)
VL
EN/HSD
DH
POK VL
DDR MAX1917 BST
V+ LX
REF DL
ILIM PGND
FSEL VTT
GND VTTR
VOUT
VTTR
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1 page  
Tracking, Sinking and Sourcing, Synchronous Buck
Controller for DDR Memory and Termination Supplies
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 12V, VEN/HSD = VDDR = 2.5V, CVL = 4.7µF, CVTTR = 1µF, CREF = 0.22µF, VFSEL = 0, ILIM = VL, PGND = LX = POK = GND,
BST = VL. Specifications are for TA = -40°C to +85°C, unless otherwise specified.) (Note 2)
PARAMETER
Reference UVLO
VTTR
VTTR Output Voltage Range
VTTR Output Accuracy
OSCILLATOR
On Time (Note 1)
Minimum Off Time (Note 1)
CURRENT LIMIT
Current-Limit Threshold
(Positive Direction)
Current-Limit Threshold
(Negative Direction)
VL REGULATOR
Output Voltage
RMS Output Current
Bypass Capacitor
FSEL LOGIC
Logic Input Current
Logic GND Level
Logic REF Level
Logic Float Level
Logic VL Level
EN/HSD LOGIC
EN/HSD Shutdown Current
Logic High
Logic Low
POWER-OK OUTPUT
Upper VTT Threshold
Lower VTT Threshold
V+ = VL = 5V
CONDITIONS
IVTTR = -5mA to +5mA
IVTTR = -25mA to +25mA, VDDR = 1.8V
IVTTR = -25mA to +25mA, VDDR = 3.6V
FSEL = VL
FSEL not connected
FSEL = REF
FSEL = GND
LX to PGND, ILIM = VL
LX to PGND, RILIM = 100kΩ
LX to PGND, RILIM = 400kΩ
LX to PGND, ILIM = VL, with percentage of positive
current-limit threshold
5.5V < V+ < 14V; 1mA < IVL < 35mA
ESR < 100mΩ
FSEL = VREF
FSEL floating
FSEL = VL
IEN/HSD for VEN/HSD = 0.8V
VL = V+ = 4.5V to 5.5V, 100mV hysteresis
VL = V+ = 4.5V to 5.5V
MIN TYP MAX UNITS
1.5 1.7 V
0
49.5
49
49.5
1.8
50.5
51
50.5
V
%VDDR
2.18
1.45
1.09
0.82
2.83
1.89
1.41
1.00
400
µs
ns
85 110
35 60 mV
160 230
-90
-130
%
4.8
2.2
1.65
3.15
VL - 0.4
0.5
1.45
110
86
5.2 V
35 mA
µF
3
0.5
2.35
3.85
µA
V
V
V
V
3.0 µA
V
0.8 V
114 %VDDR
/2
90 %VDDR
/2
_______________________________________________________________________________________ 5
5 Page 
Tracking, Sinking and Sourcing, Synchronous Buck
Controller for DDR Memory and Termination Supplies
Voltage Reference
The voltage at REF is nominally 2.00V. Connect a 0.22µF
ceramic bypass capacitor between REF and GND.
Overcurrent Protection
The current-limit circuit employs a unique “valley” cur-
rent-sensing algorithm that uses the on-state resistance
of the low-side MOSFET as a current-sensing element.
If the current-sense signal is greater than the current-
limit threshold, the PWM is not allowed to initiate a new
cycle. The actual peak current is greater than the cur-
rent-limit threshold by an amount equal to the inductor
ripple current. Therefore, the exact current-limit charac-
teristic and maximum load capability are a function of
the MOSFET on-resistance, inductor value, and input
voltage. The reward for this uncertainty is robust, loss-
less overcurrent sensing. There is also a negative cur-
rent limit that prevents excessive reverse inductor
currents when VOUT is sinking current. The negative
current-limit threshold is set to approximately 110% of
the positive current limit, and tracks the positive current
limit when ILIM is adjusted. The current-limit threshold
can be adjusted with an external resistor (RILIM) at ILIM.
A precision 5µA pullup current source at ILIM sets a
voltage drop on this resistor, adjusting the current-limit
threshold from <50mV to >200mV. In the adjustable
mode, the current-limit threshold voltage is precisely
1/10th the voltage seen at ILIM.
Therefore, choose RILIM equal to 2kΩ/mV of the cur-
rent-limit threshold. The threshold defaults to 100mV
when ILIM is connected to VL. The logic threshold for
switchover to the 100mV default value is approximately
VL - 1V. The adjustable current limit can accommodate
various MOSFETs. A capacitor in parallel with RILIM can
provide a variable soft-start function.
Carefully observe the PC board layout guidelines to
ensure that noise and DC errors do not corrupt the cur-
rent-sense signals seen by LX and PGND. The IC must
be mounted close to the low-side MOSFET with short,
direct traces making a Kelvin-sense connection to the
source and drain terminals. See the PC Board Layout
section.
Voltage Positioning
The quick-PWM control architecture responds virtually
instantaneously to transient load changes and elimi-
nates the control loop delay of conventional PWM con-
trollers. As a result, a large portion of the voltage
deviation during a step load change is from the equiva-
lent series resistance (ESR) of the output capacitors.
For DDR termination applications, the maximum
allowed voltage deviation is ±40mV for any output load
transition from sourcing current to sinking current.
Passive voltage positioning adjusts the converter’s out-
put voltage based on its load current to optimize tran-
sient response and minimize the required output
capacitance. Voltage positioning is implemented by
connecting a 2mΩ resistor as shown in Figure 1.
MOSFET Drivers
The DH and DL drivers are optimized for driving mod-
erate-size, high-side and larger, low-side power
MOSFETs and are optimized for 2.5V and 5V input volt-
ages. The drivers are sized to drive MOSFETs that can
deliver up to 25A output current. An adaptive dead-
time circuit monitors the DL output and prevents the
POK VL
V+ BST
DDR MAX1917 DH
EN/HSD
LX
REF DL
ILIM PGND
FSEL VTT
GND VTTR
VIN
RDRP
2mΩ
4 x 270µF
2V
VOUT
VTTR
POK VL
V+ BST
DDR MAX1917 DH
RBST
EN/HSD
LX
REF DL
ILIM PGND
FSEL VTT
GND VTTR
Figure 1. Using a Resistor for Voltage Positioning
Figure 2. Increasing the On Time of the High-Side MOSFET
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet MAX1917.PDF ] | |
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