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| 型号： | FAN1577AMX |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 11/15页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST PWM VM 20-SOIC |
| 标准包装： | 1 |
| PWM 型： | 电压模式 |
| 输出数： | 2 |
| 频率 - 最大： | 372kHz |
| 占空比： | 95% |
| 电源电压： | 10 V ~ 15 V |
| 降压： | 是 |
| 升压： | 是 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 20-SOIC（0.295"，7.50mm 宽） |
| 包装： | 标准包装 |
| 其它名称： | FAN1577AMXDKR |
Functional Description
The FAN1577A is a dual-channel voltage-mode PWM
controller with two sets of synchronous MOSFET driving
circuits. The two channels are running 180-degrees out
of phase. FAN1577A has the following advantages.
Soft Start
An internal startup current (35/15μA) flows out of SS/EN
pin to charge an external capacitor. During the startup
sequence, FAN1577A isn’t enabled until the SS/ENB
pin is higher than 1.2V. From 1.2V to (1.2 + 1.6 x D ON /
D ON_MAX ) V, the PWM duty cycle gradually increases
following the SS/ENB pin voltage to bring output rising.
After (1.2 + 1.6 x D ON / D ON_MAX ) V, the soft-start period
ends and the SS/ENB pin continually rises to 4.8V.
When input power is abnormal, the external capacitor
on the SS pin is shorted to ground to disable the chip.
5
C SS1 × (1.4V - 1.2V) = 35uA × t 1 ; C SS1 × (1.2V + 1.6 × 12 - 1.4V) = 15 μ A × t 2
0.9
; t 1 + t 2 = t SS1
3.3
Error Amplifier
The IN1 and IN2 pins are connected to the
corresponding internal error amplifier’s inverting input
and the outputs of the error amplifiers are connected to
the corresponding COMP1 and COMP2 pins. The
COMP1 and COMP2 pins are available for control-loop
compensation externally. Non-inverting inputs are
internally tied to a fixed 0.7V ±1.5% reference voltage.
Oscillator Operation
The FAN1577A has a programmable-frequency
oscillator. The oscillator is running at 61kHz when the
RT pin is floating. The oscillator frequency can be
adjusted from 61kHz up to 340kHz by an external
resistor R RT between the RT pin and ground. The
oscillator generates a sawtooth wave that has a 90%
rising duty. The sawtooth wave voltage threshold is
from 1.2V to 2.8V. The frequency of oscillator can be
programmed according to the following equation:
C SS2 × (1.4V - 1.2V) = 35 μ A × t 1 ; C SS2 × (1.2V + 1.6 × 12 - 1.4V) = 15 μ A × t 2
0.9
; t 1 + t 2 = t SS2
(1)
f OSC , R T (kHz) = 61kHz + 8522 / R RT (k ? )
(3)
C SS1 × 1.2V = 35 μ A × t 3 ;
; t 4 - t 3 = t time - shift
C SS2 × 0.3V
15 μ A
+
C SS2 × (1.2V - 0.3V)
35 μ A
= t 4
Setting the Output Voltage
The FAN1577A can be set from 0.7V to 90% of V IN . The
output voltages are independently adjusted by voltage
Over-Current Protection (OCP)
Over-current protection is implemented by sensing the
dividers (R 1 and R f in Figure 31) connected to INx. The
external resister dividers can be calculated by:
voltage drop across the drain and source of the external
high-side MOSFET. Over-current protection is triggered
when the voltage drop on external high-side MOSFET
V OUT = 0.7 × (1+R 1 /R f )
(4)
(high-side driver is turned off). The hysteresis is 20 C.
R DS(ON) is greater than the programmable current-limit
voltage threshold. 120μA flowing through an external
resistor between input voltage and the CLP pin sets the
threshold of current limit voltage. When over-current
condition is TRUE, the system is protected against the
cycle-by-cycle current limit. A counter counts a series of
over-current peak values for eight cycles; the soft-start
capacitor is discharged by a 50μA current until the
voltage on SS pin reaches 1.2V. During the discharge
period, the high-side driver is turned off and the low-
side driver is turned on. Once the voltage on the
SS/ENB pin is under 1.2V, the normal soft-start
sequence is initiated and the 35/15μA current charges
the soft-start capacitor again.
Output Driver
The high-side gate drivers need an external
bootstrapping circuit to provide the required boost
voltage. The highest gate driver’s output (15V is the
allowed) on the high-side and low-side MOSFETs
forces external MOSFETs to have the lowest R DS(ON) ,
which results in higher efficiency.
Over-Temperature Protection (OTP)
The device is over-temperature protected. When chip
temperature is over 150°C, the chip enters 3-state
°
I L(OCP) = [(R SENSE x I OCSET + V OFFSET ) / R DS(ON) -
(V IN - V OUT ) x V OUT / (f OSC x L OUT x V IN x 2) ]
(2)
where V OFFSET ( ≒ 10mV) is the offset voltage
contributed by the internal OCP comparator.
? 2010 Fairchild Semiconductor Corporation
FAN1577A ? Rev. 1.0.0
11
www.fairchildsemi.com
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相关代理商/技术参数 |
参数描述 |
|---|---|
| FAN1581 | 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:5A Adjustable/Fixed Ultra Low Dropout Linear Regulator |
| FAN1581D15X | 功能描述:低压差稳压器 - LDO 5A Adjustable Low Dropout Voltage Regulator (LDO) RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| FAN1581D25X | 功能描述:低压差稳压器 - LDO 5A Adjustable Low Dropout Voltage Regulator (LDO) RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| FAN1581DX | 功能描述:低压差稳压器 - LDO RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| FAN1581M | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Positive Adjustable Voltage Regulator |
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