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| 型号： | MAX1809ETI+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 13/17页 |
| 文件大小： | 0K |
| 描述： | IC DDR TERMINATION 28-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 应用： | 转换器，DDR |
| 输入电压： | 3 V ~ 5.5 V |
| 输出数： | 1 |
| 输出电压： | 1.1 V ~ 5.5 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-SSOP（0.154"，3.90mm 宽） |
| 供应商设备封装： | 16-QSOP |
| 包装： | 带卷 (TR) |
3A, 1MHz, DDR Memory Termination Supply
INPUT VOLTAGE
(3V TO 5.5V)
IN
LX
L
V TT = V DDQ /2
C IN
FB
10 ?
MAX1809
C OUT
SHDN
2.2 μ F
V CC
PGND
GND
V DDQ
(a)
2N7002
(2.5V)
(b)
SHDN
SHDN
10k ?
0.1 μ F
EXTREF
10k ?
0.1 μ F
V SSQ
Figure 9. Discharging the Output of the MAX1809 in Shutdown
Pin Configurations (continued)
INPUT VOLTAGE
(3V TO 5.5V)
IN
LX
L
V TT =V DDQ /2
TOP VIEW
SHDN 1
16 LX
10 ?
2.2 μ F
C IN
V CC
MAX1809
FB
PGND
GND
100 ?
C OUT
IN 2
LX 3
IN 4
MAX1809
15 PGND
14 LX
13 PGND
SS 5
12 V CC
SHDN
SHDN
SS
0.01 μ F
EXTREF 6
TOFF 7
11 GND
10 REF
FB 8
9
GND
Figure 10. Starting the MAX1809 in Sinking Mode with V OUT
>V EXTREF
the dissipation in the termination resistor is halved com-
pared to a termination scheme that connects the resistive
terminators to ground.
The V TT supply requires that it regulates to half the
memory voltage (V DDQ ), tracks the changes of the
memory voltage, and is able to source and sink current
depending on the state of the bus. These requirements
are met in the MAX1809.
Discharging the Output in Shutdown
When SHDN is brought low after the controller has
been on for a while, the output may remain high if there
is no leakage or discharge path to bring the output
down. For DDR memory systems, keeping V TT at 1.25V
when V DDQ (2.5V) is shut down violates the DDR speci-
fications. This can result in the bus latching if the sys-
QSOP
tem is subsequently turned on or possibly damaging
the memory subsystem.
When using the MAX1809 to generate the V TT output of
1.25V, several circuits are recommended to discharge
the output when the MAX1809 is shut down. These are
shown in Figure 9. Solution (a) is a diode added from
V TT to V DDQ so that V TT is discharged when VDDQ
goes low. Alternatively, solution (b) uses a small signal
transistor to discharge V TT when the MAX1809 is shut
down.
Startup in Sinking Mode
The MAX1809 will not startup until the feedback voltage
is made less than the external reference voltage when
power is applied or when the part is exiting shutdown.
In applications that cannot guarantee V FB < V EXTREF
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