参数资料
| 型号： | ISL95872HRUZ-T |
| 厂商： | Intersil |
| 文件页数： | 8/17页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM 16UTQFN |
| 标准包装： | 3,000 |
| PWM 型： | R4 |
| 输出数： | 1 |
| 频率 - 最大： | 300kHz |
| 电源电压： | 4.75 V ~ 5.25 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： | -10°C ~ 100°C |
| 封装/外壳： | 16-UFQFN |
| 包装： | 带卷 (TR) |
ISL95872
------------------- = ------------------- ? -------------------- 2 -
dV EXT I SS R 1 + R
C SOFT
R 2
Theory of Operation
The following sections will provide a detailed description of the
inner workings of the ISL95872.
Power-On Reset
The IC is disabled until the voltage at the VCC pin has increased
above the rising power-on reset (POR) threshold voltage
V VCC_THR . The controller will become disabled when the voltage
at the VCC pin decreases below the falling POR threshold voltage
V VCC_THF . The POR detector has a noise filter of approximately
1μs.
Enabling the Controller
Once VCC has ramped above V VCC_THR , the controller can be
enabled by pulling the EN pin voltage above the input-high
threshold V ENTHR . Once EN exceeds this threshold, the soft-start
sequence is initiated.
External Reference Setup
The REFIN input of the ISL95872 requires an external reference
voltage to be connected to this pin. Typically, this will be another
system rail which requires the output of the ISL95872 to follow it
up during boot-up of the two regulators. A resistor divider is
required between the external reference voltage and the REFIN
pin to scale the external voltage down to the internal reference
voltage, see Figure 5.
Soft-Start
Once the POR threshold on VCC has been met and ENABLE is
applied, the SREF pin releases its discharge clamp, and enables
the reference amplifier V SET . The soft-start current I SS is limited
to 85μA and is sourced out of the SREF pin and begins charging
the C SOFT capacitor on the SREF pin until it equals V REFIN . The
soft-start current will adjust to match the external reference
ramp rate as seen through the resistor divider on the REFIN pin.
The regulator controls the PWM such that the voltage on the
SREF pin tracks the rising voltage on the REFIN pin. The
maximum dv/dt that the external voltage (V EXT ) can achieve is
outlined in Equation 2.
(EQ. 2)
dt
The elapsed time from when the EN pin is asserted to when
V SREF has charged C SOFT to V REF IN will depend on the dv/dt of
the external reference voltage used to generate the signal at
REFIN. C SOFT will not impact the dv/dt unless it is over sized or
the dv/dt, outlined in Equation 2, is exceeded by the external
reference. The minimum C SOFT capacitance is 10nF.
Once the feedback voltage, FB, exceeds the 0.482V threshold on
an internal comparator, the ISL95872 switches from the external
reference (V EXT ) to the internal reference, V REF , see Figure 6. The
end of soft-start is detected by I SS tapering off when capacitor
C SOFT charges to V REFIN . The pull-down on PGOOD is released to
indicate that the controller is regulating properly.
V OUT
R FB
FB
?
EA
V COMP
V EXT
Slope determined
by load current
+
+
V REF
SREF
V SET
?
V REF
?
+
V REFIN
V EXT
REFIN
V REFIN
0.482V
R 1
R 2
FB
FIGURE 6. SOFT-START TRACKING OF EXTERNAL REFERENCE
FIGURE 5. REFIN CONNECTION TO SYSTEM RAIL
The relation between the voltage at the REFIN pin, V REFIN , and
the external reference voltage, V EXT , is given in Equation 1:
During soft-start, the regulator always operates in CCM until the
soft-start sequence is complete. Once soft-start is complete
diode emulation mode (DEM) is enabled.
Output Voltage Programming
V REFIN = V REF = V EXT ? ---------------------
R 2
R 1 + R 2
From this expression the resistor divider values can be
calculated. The voltage on the REFIN pin must equal to the
internal reference of the ISL95872.
(EQ. 1)
The ISL95872 has a fixed 0.5V internal reference voltage
(V SREF ). As shown in Figure 7, the output voltage is the reference
voltage if R FB is shorted and R OFS is open. A resistor divider
consisting of R OFS and R FB allows the user to scale the output
voltage between 0.5V and 3.3V. The relation between the output
voltage and the reference voltage is given in Equation 3:
V OUT = V REF ? ----------------------------------
R
8
R FB + R OFS
OFS
(EQ. 3)
FN7974.0
January 26, 2012
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| ISL95873HRUZ-T | 功能描述:电流型 PWM 控制器 2-Bit PWM GPU Controller for Toshiba. Spin of ISL95872; 2.6 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 |
| ISL95874HRUZ-T | 功能描述:电流型 PWM 控制器 0/2 BIT PWM GPU CONTLR FOR NOTEBOOK 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 |
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