参数资料
| 型号： | ISL6539IA-T |
| 厂商： | Intersil |
| 文件页数： | 10/20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
Q1
V IN
Feedback Loop Compensation
Both channel PWM controllers have internally compensated
UGATE
ISEN
R CS
L1
error amplifiers. To make internal compensation possible,
several design measures were taken.
? The ramp signal applied to the PWM comparator has been
LGATE
Q2
C1
Cz
R1
made proportional to the input voltage by the VIN pin. This
keeps the product of the modulator gain and the input
voltage constant even when the input voltage varies.
VOUT
VSEN
? The load current proportional signal is derived from the
voltage drop across the lower MOSFET during the PWM
ISL6539
OCSET
R OC
R2
off time interval, and is subtracted from the error amplifier
output signal before the PWM comparator input. This
effectively creates an internal current control loop.
FIGURE 6. THE INTERNAL COMPENSATOR
Current Sensing
The current on the lower MOSFET is sensed by measuring
its voltage drop within its on-time. In order to activate the
current sampling circuitry, two conditions need to be met. (1)
The resistor connected to the ISEN pin sets the gain in the
current sensing. The following expression estimates the
required value of the current sense resistor, depending on
the maximum continuous load current, and the value of the
MOSFETs r DS(ON) , assuming the ISEN pin sources 75μA
current.
I MAX ? r DS ( ON )
the LGATE is high and (2) the phase pin sees a negative
voltage for regular buck operation, which means the current
is freewheeling through lower MOSFET. For the second
75 μ A
R CS = ------------------------------------------ – 140 Ω
(EQ. 5)
channel of the DDR application, the phase pin voltage needs
to be higher than 0.1V to activate the current sensing circuit
for bidirectional current sensing. The current sampling
finishes at about 400ns after the lower MOSFET has turned
on. This current information is held for current mode control
and overcurrent protection. The current sensing pin can
source up to 260μA. The current sense resistor and OCSET
resistor can be adjusted simultaneously for the same
overcurrent protection level; however, the current sensing
Because the current sensing circuit is a sample-and-hold
type, the information obtained at the last moment of the
sampling is being used. This current sensing circuit samples
the inductor current very close to its peak value. The current
feedback essentially injects a resistor R i in series with the
original LC filter as shown in Figure 7, where the
sample-and-hold effect of the current loop has been ignored.
V c and V o are small signal components extracted from its
DC operation points.
gain will be changed only according to the current sense
resistor value, which will affect the current feedback loop
gain. The middle point of the ISEN current can be at 75μA,
Ri
Lo
DCR
Co
+
but it can be tuned up and down to fit application needs.
If another channel is switching at the moment the current
sample is finishing, it could cause current sensing error and
Gm*Vc
+
-
ESR
Ro
Vo
-
phase voltage jitter. In the design stage, the duty cycles and
synchronization have to be analyzed for all the input voltage
and load conditions to reduce the chance of current sensing
error. The relationship between the sampled current and
MOSFET current is given by Equation 4:
FIGURE 7. THE EQUIVALENT CIRCUIT OF THE POWER
STAGE WITH CURRENT LOOP INCLUDED
The value of the injected resistor can be estimated by
Equation 6:
R i = ----------------- ---------------------------- ? 4.4k Ω
I SEN ( R CS + 140 ) = r DS ( ON ) I D
(EQ. 4)
V IN r DS ( ON )
V ramp R CS + 140
(EQ. 6)
Which means the current sensing pin will source current to
make the voltage drop on the MOSFET equal to the voltage
generated on the sensing resistor, plus the internal resistor,
along the ISEN pin current flowing path.
10
R i is in k Ω, and r DS and R CS are in Ω . V IN divided by V ramp ,
is defined as Gm, which is a constant 8dB or 18dB for both
channels in dual switcher applications, when V IN is above
3V. Refer to Tables 1 and 2 for the ramp amplitude in
different V IN pin connections. The feed-forward effect of the
V IN is reflected in Gm. V c is defined as the error amplifier
output voltage.
FN9144.6
April 29, 2010
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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 |
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