参数资料
| 型号： | ISL6539IA-T |
| 厂商： | Intersil |
| 文件页数： | 15/20页 |
| 文件大小： | 0K |
| 描述： | IC CTRLR DDR DRAM, SDRAM 28QSOP |
| 标准包装： | 2,500 |
| 应用： | 控制器，DDR DRAM，SDRAM |
| 输入电压： | 3.3 V ~ 18 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-SSOP（0.154"，3.90mm 宽） |
| 供应商设备封装： | 28-SSOP/QSOP |
| 包装： | 带卷 (TR) |
ISL6539
Sometimes, if the phase node is very noisy, a resistor can be
put on the ISEN pin to ground. This resistor together with the
R CS can divide the phase node voltage down, seen by the
internal current sense amplifier, and reduce noise coupling.
Sizing the Overcurrent Setpoint Resistor
The internal 0.9V reference is buffered to the OCSET pin
with a voltage follower (refer to the equivalent circuit in
Figure 12). The current going through the external
overcurrent set resistor is sensed from the OCSET pin. This
current, divided by 2.9, sets up the overcurrent threshold and
compares with the scaled ISEN pin current going through
R CS with an 8μA offset. Once the sensed current is higher
than the threshold value, an OC signal is generated. The first
OC signal starts a counter and activates a pulse skipping
function. The inductor current will be continuously monitored
through the phase node voltage after the first OC trip. As
long as the sensed current exceeds the OC threshold value,
the following PWM pulse will be skipped. This operation will
be the same for 8 switching cycles. Another OC occurring
between 8 to 16 switching cycles would result in a latch off
The MOSFET will not heat-up when applying a very low
frequency and short load pulses with an electronic load to
the output.
As an example, assume the following:
? The maximum normal operation load current is 1
? The OC set point is 10% higher than the maximum load
current
? The inductor peak current is 1.15 to 1.3 times higher than
the load current, depending on the inductor value and the
input voltage
? The r DS(ON) has a 45% increase at higher temperature
I OC should set at least 1.8 to 2 times higher than the
maximum load current to avoid nuisance overcurrent trip.
Selection of the LC Filter
The duty cycle of a buck converter is a function of the input
voltage and output voltage. Once an output voltage is fixed,
it can be written as Equation 18:
D ( V IN ) = ----------------
with both upper and lower drives low. If there is no OC within
8 to 16 switching cycles, normal operation resumes.
V OUT
V IN
(EQ. 18)
The switching frequency, f sw , of ISL6539 is 300kHz. The
peak-to-peak ripple current going through the inductor can
PHASE R CS
ISEN
140 Ω
_
be written as Equation 19:
+ Σ + 8uA
f sw ? L
_
+
DS(ON)
r Rdson
+
÷ 33.1
8μA
V OUT ( 1 – D ( V IN ) )
I P – P = --------------------------------------------------
(EQ. 19)
Rset
OCSET
Amplifier
AMPLIFIER
_
+
0.9 V
Reference
REFERENC E
÷ 2.9
SENSE
I Isense
+ OC
_
Comparator
COMPARATOR
As higher ripple current will result in higher switching loss
and higher output voltage ripple, the peak-to-peak current of
the inductor is generally designed with a 20% to 40%
peak-to-peak ripple of the nominal operation current. Based
on this assumption, the inductor value can be selected with
Equation 19. In addition to the mechanical dimension, a
shielded ferrite core inductor with a very low DC resistance,
DCR, is preferred for less core loss and copper loss. The DC
FIGURE 12. EQUIVALENT CIRCUIT FOR OC SIGNAL
GENERATOR
copper loss of the inductor can be estimated by Equation 20:
P copper = I load DCR
2
(EQ. 20)
R set = ---------------------------------------------------
I OC r DS ( ON ) (EQ. 17)
10.3V
--------------------------------- + 8 μ A
R CS + 140
I OC is the inductor peak current and not the load current.
Since inductor peak current changes with input voltage, it is
better to use an oscilloscope when testing the overcurrent
setting point to monitor the inductor current, and to
determine when the OC occurs. To get consistent test results
on different boards, it is best to keep the MOSFET at a fixed
temperature.
15
The inductor copper loss can be significant in the total
system power loss. Attention has to be given to the DCR
selection. Another factor to consider when choosing the
inductor is its saturation characteristics at elevated
temperature. Saturated inductors could result in nuisance
OC, or OV trip.
Output voltage ripple and the transient voltage deviation are
factors that have to be taken into consideration when
selecting an output capacitor. In addition to high frequency
noise related MOSFET turn-on and turn-off, the output voltage
ripple includes the capacitance voltage drop and ESR voltage
FN9144.6
April 29, 2010
相关PDF资料 |
PDF描述 |
|---|---|
| ISL6540AIRZA-T | IC REG CTRLR BUCK PWM VM 28-QFN |
| ISL65426HRZ | IC REG BUCK SYNC ADJ 6A DL 50QFN |
| ISL6545IBZ-T | IC REG CTRLR BUCK PWM VM 8-SOIC |
| ISL6548ACRZA-T | IC REG/CTLR ACPI DUAL DDR 28QFN |
| ISL6548CRZA | IC REG/CTRLR ACPI DUAL DDR 28QFN |
相关代理商/技术参数 |
参数描述 |
|---|---|
| ISL6539IAZ | 功能描述:电流型 PWM 控制器 ISL6539 DL SWITCHER 15V INDUSTRIAL GRD 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 |
| ISL6539IAZ-T | 功能描述:电流型 PWM 控制器 ISL6539 DL SWITCHER 15V INDUSTRIAL GRD 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 |
| ISL6540ACRZ | 功能描述:IC REG CTRLR BUCK PWM VM 28-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:75 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.3 V ~ 13.5 V 降压:是 升压:是 回扫:是 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:0°C ~ 70°C 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:管件 产品目录页面:1051 (CN2011-ZH PDF) 其它名称:296-2543-5 |
| ISL6540ACRZ-T | 功能描述:IC REG CTRLR BUCK PWM VM 28-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
| ISL6540ACRZ-TR5453 | 制造商:Intersil Corporation 功能描述:STD. ISL6540ACRZ-T W/GOLD BOND WIRE ONLY - Tape and Reel |
发布紧急采购，3分钟左右您将得到回复。