参数资料
| 型号： | FAN5026MTC |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 10/17页 |
| 文件大小： | 0K |
| 描述： | IC CONTROLLER DDR 28TSSOP |
| 产品变化通告： | Mold Compound Change 30/Nov/2007 |
| 标准包装： | 49 |
| 应用： | 控制器，DDR |
| 输入电压： | 3 V ~ 16 V |
| 输出数： | 2 |
| 输出电压： | 0.9 V ~ 5.5 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-TSSOP（0.173"，4.40mm 宽） |
| 供应商设备封装： | 28-TSSOP |
| 包装： | 管件 |
| 其它名称： | FAN5026MTC_NL FAN5026MTC_NL-ND |
Initialization and Soft Start
Assuming EN is HIGH, FAN5026 is initialized when V CC
exceeds the rising UVLO threshold. Should V CC drop
Since
=
?
100 +
(
)
(3b)
below the UVLO threshold, an internal power-on reset
function disables the chip.
and at the ILIM 0.9V threshold:
The voltage at the positive input of the error amplifier is
limited by the voltage at the SS pin, which is charged
= 12 ?
0.9
=
10.8
(3c)
with a 5 μ A current source. Once C SS has charged to
V REF (0.9V) the output voltage is in regulation. The time
it takes SS to reach 0.9V is:
therefore:
t 0 . 9 =
0 . 9 xC SS
5
(1)
=
10.8 100 +
?
(
)
(3d)
where t 0.9 is in seconds if C SS is in F.
When SS reaches 1.5V, the power-good outputs are
enabled and Hysteretic Mode is allowed. The converter
is forced into PWM Mode during soft-start.
Current Processing Section
The following discussion refers to Figure 12.
Current limit (I LIMIT ) should be set high enough to allow
inductor current to rise in response to an output load
transient. Typically, a factor of 1.2 is sufficient. In
addition, since I LIMIT is a peak current cut-off value,
multiply I LOAD(MAX) by the inductor ripple current (e.g.
25%). For example, in Figure 6, the target for I LIMIT :
I LIMIT > 1.2 x 1.25 x 1.6 x 2A ≈ 5A
The current through the R SENSE resistor (I SNS ) is
sampled (typically 400ns) after Q2 is turned on, as
shown in Figure 12. That current is held and summed
with the output of the error amplifier. This effectively
=
10.8 100 +
?
(
)
(4)
creates a current-mode control loop. The resistor
connected to ISNSx pin (R SENSE ) sets the gain in the
current feedback loop. For stable operation, the voltage
induced by the current feedback at the PWM
comparator input should be set to 30% of the ramp
amplitude at maximum load current and line voltage.
The following expression estimates the recommended
value of R SENSE as a function of the maximum load
current (I LOAD(MAX) ) and the value of the MOSFET
R DS(ON) :
Since the tolerance on the current limit is largely
dependent on the ratio of the external resistors, it is
fairly accurate if the voltage drop on the switching-node
side of R SENSE is an accurate representation of the load
current. When using the MOSFET as the sensing
element, the variation of R DS(ON) causes proportional
variation in the I SNS . This value varies from device to
device and has a typical junction temperature
coefficient of about 0.4%/°C (consult the MOSFET
=
( ) ?
30% ? 0.125 ?
(
)
(
? 4.1
)
? 100
(2a)
datasheet for actual values), so the actual current limit
set point decreases proportional to increasing MOSFET
die temperature. A factor of 1.6 in the current limit set
point should compensate for MOSFET R DS(ON)
R SENSE must, however, be kept higher than:
variations, assuming the MOSFET heat sinking keeps
its operating die temperature below 125°C.
=
(
) ?
150 μ
(
)
? 100
(2b)
LDRV
Q2
The 100 is the internal resistor in series with the
ISNSx pins and has ±15% typical variation. Because
R SENSE is in series with the internal 100 resistor, the
gain in the current feedback loop and the current limit
accuracy is affected if R SENSE is close to 100 .
ISNS
PGND
R SENSE
Setting the Current Limit
A ratio of I SNS is compared to the current established
when a 0.9V internal reference drives the ILIM pin. The
Figure 11.
Improving Current-Sensing Accuracy
threshold is determined as follows:
More accurate sensing can be achieved by using a
resistor (R1) instead of the R DS(ON) of the FET, as shown
9
=
4
3
= 12 ?
(3a)
in Figure 11. This approach causes higher losses, but
yields greater accuracy in both V DROOP and I LIMIT . R1 is a
low value resistor (e.g. 10m ? ).
? 2005 Fairchild Semiconductor Corporation
FAN5026 ? Rev. 1.0.8
10
www.fairchildsemi.com
相关PDF资料 |
PDF描述 |
|---|---|
| FAN5234MTCX | IC PWM CTLR/PFM MOBILE 16TSSOP |
| FAN5236MTC | IC DDR/PWM CTRLR DUAL 28TSSOP |
| FAN5350MPX | IC REG BUCK SYNC 1.82V 0.6A 6MLP |
| FAN5353MPX | IC REG BUCK SYNC ADJ 3A 12MLP |
| FAN5354MPX | IC REG BUCK SYNC ADJ 3A 12MLP |
相关代理商/技术参数 |
参数描述 |
|---|---|
| FAN5026MTC_Q | 功能描述:电流型 PWM 控制器 PFC Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| FAN5026MTCX | 功能描述:电流型 PWM 控制器 PFC Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| FAN5029 | 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:8-Bit Programmable 2- to 5-Phase Synchronous Buck Controller |
| FAN5029 WAF | 制造商:Fairchild Semiconductor Corporation 功能描述: |
| FAN5029_07 | 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:8-Bit Programmable 2- to 5-Phase Synchronous Buck Controller |
发布紧急采购，3分钟左右您将得到回复。