CXSD6293单相的时间恒定的同步的驱动N通道mosfet的PWM控制器满足低输出电压应用的要求

目录

1.产品概述                       2.产品特点
3.应用范围                       4.下载产品资料PDF文档 
5.产品封装图                     6.电路原理图                   
7.功能概述                        8.相关产品

一,产品概述(General Description)    

      The CXSD6293 is a single-phase, constant-on-time, and  synchronous
PWM controller, which drives N-channel MOSFETs. An internal 0.5V temperature-compensated reference voltage with high accuracy is designed to meet the
requirement of low output voltage applications. The CXSD6293 steps down
high voltage to generate low-volt-age chipset or RAM supplies in notebook
computers.The PWM controller operates fixed 300kHz pseudo-con-
stant frequency PWM with an adaptive constant-on-time control. The device
provides excellent transient response and accurate DC voltage output in either
PFM or PWM Mode. In Pulse Frequency Mode (PFM), the CXSD6293 pro-
vides very high efficiency over light to heavy loads with loading-modulated
switching frequencies. The device works in ultrasonic mode with PFM at no
load. The unique ultrasonic mode maintains the switching frequency above
20kHz, which eliminates noise in audio applications.
          The CXSD6293 is equipped with accurate over-current,output
under-voltage, and output over-voltage protections.A Power-On-Reset
function monitors the voltage on VCC to prevent wrong operation during
power-on. The CXSD6293 has a 1.5ms digital soft-start to ramp up the
output voltage to reduce the start-up current. A soft-stop function actively
discharges the output capacitors with controlled reverse inductor current.
The CXSD6293 is available in TDFN3x3-10 package
二.产品特点(Features)

1.)Operates from An Input Battery Voltage Range of +3V to +25V
      ±0.6% 0.5V Reference Over Line, Load Regulation, and
      Operating Temp. 
2.)Drive Dual Low Cost N-Channel MOSFETs
    Adaptive Shoot-Through Protection 
3.)Power-On-Reset Monitoring on VCC Pin
4.)PFM Mode for Increasing Light Load Efficiency
5.)Constant-On-Time Control Scheme
     Switching Frequency Compensation for PWM Operation
6.)300kHz Constant Switching Frequency
7.)Integrated MOSFET Drivers and Bootstrap Diode
8.)Internal Soft-Start and Soft-Stop
9.)Power Good Monitoring
10.)70% Under-Voltage Protection
11.)125% Over-Voltage Protection
     Using Low-Side MOSFET’s RDS(ON)
12.)Over-Temperature Protection
13.)TDFN-10 3mmx3mm Package
14.)Lead Free and Green Devices Available (RoHS Compliant)
三,应用范围 (Applications)

Notebook
Low Cost PC
Wide Input DC/DC Regulators
四.下载产品资料PDF文档 

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五,产品封装图 (Package)

六.电路原理图

七,功能概述

Constant-On-Time PWM Controller with Input Feed-For-ward
The constant-on-time control architecture is a pseudo-fixed frequency with input voltage feed-forward. This ar-
chitecture relies on the output filter capacitor’s effective series resistance (ESR) to act as a current-sense resis-
tor so the output ripple voltage provides the PWM ramp signal. In PFM operation, the high-side switch on-time is
controlled by the on-time generator is determined solely by a one-shot whose pulse width is inversely propor-
tional to the input voltage and directly proportional to the output voltage. In PWM operation, the high-side switch
on-time is determined by a switching frequency control circuit in the on-time generator block.The switching
frequency control circuit senses the switch-ing frequency of the high-side switch and keeps regulat-
ing it at a constant frequency in PWM mode. The design improves the frequency variation and is more outstand-
ing than a conventional constant-on-time controller, which has large switching frequency variation over input

 voltage,output current, and temperature. Both in PFM and PWM,the on-time generator, which senses input 

voltage on PHASE pin, provides very fast on-time response to input line transients.Another one-shot sets a 

minimum off-time (typical:300ns). The on-time one-shot is triggered if the error com-parator is high, the

 low-side switch current is below the current-limit threshold, and the minimum off-time one-shot has 

timed out. 
Pulse-Frequency Modulation (PFM)
In PFM mode, an automatic switchover to pulse-frequency modulation (PFM) takes place at light loads. This
switchover is affected by a comparator that truncates the low-side switch on-time at the inductor current zero
crossing. This mechanism causes the threshold between PFM and PWM operation to coincide with the boundary
between continuous and discontinuous inductor-current operation (also known as the critical conduction point).
The on-time of PFM is given by:
Ultrasonic Mode
The ultrasonic mode activates an unique PFM mode with a minimum switching frequency of 20kHz. The minimum
frequency 20kHz of ultrasonic mode eliminates audio-frequency interference in light load condition. It will transit
to unique PFM mode when output loading makes the frequency bigger than ultrasonic frequency.
In ultrasonic mode, the controller automatically transits to fixed-frequency PWM operation when the load reaches
the same critical conduction point (ILOAD(PFM to PWM)).When the controller detects that no switching has oc-
curred within about 40μs (Typical), an ultrasonic pulse will be occurred. The ultrasonic controller turns on the
low-side MOSFET firstly to reduce the output voltage. After feedback voltage drops below the internal reference
voltage, the controller turns off the low-side MOSFET and triggers a constant-on-time. When the constant-on-

time has expired, the controller turns on the low-side MOSFET again until the inductor current is below the 

zero-cross-ing threshold. The behavior is the same as PFM mode. 
Power-On-Reset (POR)
A Power-On-Reset (POR) function is designed to prevent wrong logic controls when the VCC voltage is low. The
POR function continually monitors the bias supply volt-age on the VCC pin if at least one of the enable pins is set
high. When the rising VCC voltage reaches the rising POR voltage threshold (4.2V, typical), the POR signal goes
high and the chip initiates soft-start operations. When this voltage drops lower than 4.0V (typical), the POR dis-
ables the chip.

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