LTC3717 Datasheet, PDF (1/20 Pages) Linear Technology – Wide Operating Range, No RSENSE Step-Down Controller for DDR/QDR Memory Termination

LTC3717
Wide Operating Range,
No R_SENSE^TM Step-Down Controller
for DDR/QDR Memory Termination
FEATURES
s _{VOUT = 1/2 VIN (Supply Splitter)}
s _{Adjustable and Symmetrical Sink/Source}
Current Limit up to 20A
s _{±0.65% Output Voltage Accuracy}
s _{Up to 97% Efficiency}
s _{No Sense Resistor Required}
s _{Ultrafast Transient Response}
s _{True Current Mode Control}
s _{2% to 90% Duty Cycle at 200kHz}
s _{tON(MIN) ≤ 100ns}
s _{Stable with Ceramic COUT}
s _{Dual N-Channel MOSFET Synchronous Drive}
s _{Power Good Output Voltage Monitor}
s _{Wide VCC Range: 4V to 36V}
s _{Adjustable Switching Frequency up to 1.5MHz}
s _{Output Overvoltage Protection}
s _{Optional Short-Circuit Shutdown Timer}
s _{Available in a 16U-Pin Narrow SSOP Package}
APPLICATIO S
s _{Bus Termination: DDR and QDR Memory, SSTL,}
HSTL, ...
s _{Notebook Computers, Desktop Servers}
s _{Tracking Power Supply}
DESCRIPTIO
The LTC^®3717 is a synchronous step-down switching
regulator controller for double data rate (DDR) and Quad
Data Rate^TM (QDR^TM) memory termination. The controller
uses a valley current control architecture to deliver very
low duty cycles without requiring a sense resistor. Oper-
ating frequency is selected by an external resistor and is
compensated for variations in V_IN.
Forced continuous operation reduces noise and RF inter-
ference. Output voltage is internally set to half of V_REF,
which is user programmable.
Fault protection is provided by an output overvoltage
comparator and optional short-circuit shutdown timer.
Soft-start capability for supply sequencing is accom-
plished using an external timing capacitor. The regulator
current limit level is symmetrical and user programmable.
Wide supply range allows operation from 4V to 36V at the
V_CC input.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No R_SENSE is a trademark of Linear Technology Corporation.
QDR RAMs and Quad Data Rate RAMs comprise a new family of products developed by Cypress
Semiconductor, Hitachi, IDT, Micron Technology, Inc. and Samsung.
TYPICAL APPLICATIO
V_CC
5V TO 28V
1µF
V_{CC ION}
V_REF
C_C
470pF
C_SS
0.1µF
R_C
20k
RUN/SS TG
SW
I_TH
BOOST
LTC3717
SGND INTV_CC
BG
PGOOD PGND
R_ON
715k
V_DD = 2.5V
C_B 0.22µF
D_B
CMDSH-3
+
C_VCC
4.7µF
M1
Si7840DP
M2
Si7840DP
V_FB
D2
B320A
V_IN
+
2.5V TO 5.5V
C_IN
150µF
6.3V
×2
V_OUT
1.25V
L1
0.68µH
+
C_OUT ±10A
180µF
4V
×2
D1
B320A
3717 F01a
Figure 1. High Efficiency DDR Memory Termination Supply
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10
0
0
V_IN = 5V
V_IN = 2.5V
V_OUT = 1.25V
2 4 6 8 10 12 14
LOAD CURRENT (A)
3717 F01b
sn3717 3717fs
1