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参数资料
| 型号： | MAX1809ETI+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 9/17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
V IN
1400
1200
1000
I SOURCE
V OUT
800
600
V OUT = 2.5V
V OUT = 1.25V
400
200
SYNCHRONOUS BUCK MODE
(SOURCING CURRENT)
0
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
V IN
I SINK
SYNCHRONOUS BOOST MODE
(SINKING CURRENT)
V SOURCE > V OUT
V IN (V)
Figure 4. Maximum Recommended Operating Frequency vs.
Input Voltage
V PMOS = the voltage drop across the internal
PMOS power switch | I OUT ? R PMOS |
V NMOS = the voltage drop across the internal
NMOS synchronous-rectifier switch | I OUT ?
R NMOS |
f SW = switching frequency
Make sure that t ON and t OFF are greater than 400ns
( V IN ? V OUT ? V PMOS )
f SW IN PMOS NMOS )
( V ? V
t OFF =
t ON = t OFF ?
? V IN ? V OUT + V PMOS ?
Figure 3. Sourcing and Sinking Capabilities of the MAX1809
Programming the Switching Frequency
and Off-Time and On-Time
The MAX1809 features a programmable PWM-mode
switching frequency, which is set by the input and out-
put voltage and the value of R TOFF , connected from
TOFF to GND. R TOFF sets the PMOS power switch off-
time in PWM mode. Use the following equation to select
the off-time while sourcing current according to the
desired switching frequency in PWM mode:
+ V
where:
t OFF = the programmed off-time
V IN = the input voltage
V OUT = the output voltage
when sourcing current. Select R TOFF according to the
formula:
R TOFF = (t OFF - 0.07μs) ? (117k ? /1.00μs)
Recommended values for R TOFF range from 36k ? to
430k ? for off-times of 0.4μs to 4μs.
When sinking current, the switching frequency increas-
es due to the on-resistances of the internal switches
adding to the voltage across the inductor, reducing the
on-time. Calculate t ON when sinking current using the
equation:
? V OUT ? V NMOS ?
?
Check that t ON in the current sinking mode is greater
than 350ns.
Inductor Selection
The key inductor parameters must be specified: inductor
value (L) and peak current (I PEAK ). The following equa-
tion includes a constant, denoted as LIR, which is the
ratio of peak-to-peak inductor AC current (ripple current)
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