The CXSD62118 is a single-phase, constant-on-time,synchronous PWM controller, which drives N-channel MOSFETs. CXSD62118 steps down high voltage to generate low-voltage chipset or RAM supplies in no

目录qfw嘉泰姆

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</span>                     6.电路原理图</span>                   
7.功能概述                        8.相关产品qfw嘉泰姆

一,产品概述(General Description)   qfw嘉泰姆

  The CXSD62118 is a single-phase, constant-on-time,synchronous PWM controller, which drives N-channel MOSFETs. The CXSD62118 steps down high voltage to generate low-voltage chipset or RAM supplies in notebook computers.
  The CXSD62118 provides excellent transient response and accurate DC voltage output in either PFM or PWM Mode.In Pulse Frequency Mode (PFM), the CXSD62118 provides very high efficiency over light to heavy loads with loading-
modulated switching frequencies. In PWM Mode, the converter works nearly at constant frequency for low-noise requirements.
  The CXSD62118 is equipped with accurate positive current-limit, output under-voltage, and output over-voltage protections, perfect for NB applications. The Power-On-Reset function monitors the voltage on VCC to prevent wrong operation during power-on. The CXSD62118 has a 1ms digital soft-start and built-in an integrated output discharge method for soft-stop. An internal integrated
soft-start ramps up the output voltage with programmable slew rate to reduce the start-up current. A soft-stop function actively discharges the output capacitors with controlled reverse inductor current.
  The CXSD62118 is available in 10pin TDFN 3x3 package.
二</span>.产品特点(Features)qfw嘉泰姆

Adjustable Output Voltage from +0.7V to +5.5V
- 0.7V Reference Voltage
- ±1% Accuracy Over-Temperature
Operates from an Input Battery Voltage Range of
+1.8V to +28V
Power-On-Reset Monitoring on VCC Pin
Excellent Line and Load Transient Responses
PFM Mode for Increased Light Load Efficiency
Selectable PWM Frequency from 4 Preset Values
Integrated MOSFET Drivers
Integrated Bootstrap Forward P-CH MOSFET
Adjustable Integrated Soft-Start and Soft-Stop
Selectable Forced PWM or Automatic PFM/PWM Mode
Power Good Monitoring
70% Under-Voltage Protection
125% Over-Voltage Protection
Adjustable Current-Limit Protection
- Using Sense Low-Side MOSFET’s RDS(ON)
Over-Temperature Protection
TDFN-10 3x3 Package
Lead Free and Green Devices Available
三</span>,应用范围 (Applications)qfw嘉泰姆

Notebook
Table PC
Hand-Held Portable
AIO PC
四.下载产品资料PDF文档 qfw嘉泰姆

需要详细的PDF规格书请扫一扫微信联系我们，还可以获得免费样品以及技术支持</span>！</span>qfw嘉泰姆

五,产品封装图 (Package)qfw嘉泰姆

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六.电路原理图</span>qfw嘉泰姆

qfw嘉泰姆

七</span>,功能概述qfw嘉泰姆

Input Capacitor Selection (Cont.)
higher than the maximum input voltage. The maximum RMS current rating requirement is approximatelyqfw嘉泰姆

 IOUT/2,where IOUT is the load current. During power-up, the input capacitors have to handle great qfw嘉泰姆

amount of surge current.For low-duty notebook appliactions, ceramic capacitor is recommended. Theqfw嘉泰姆

 capacitors must be connected be-tween the drain of high-side MOSFET and the source of low-side qfw嘉泰姆

MOSFET with very low-impeadance PCB layout
MOSFET Selection
The application for a notebook battery with a maximum voltage of 24V, at least a minimum 30V MOSFETsqfw嘉泰姆

 should be used. The design has to trade off the gate charge with the RDS(ON) of the MOSFET:
For the low-side MOSFET, before it is turned on, the body diode has been conducting. The low-side MOSFETqfw嘉泰姆

 driver will not charge the miller capacitor of this MOSFET.In the turning off process of the low-side MOSFET,qfw嘉泰姆

 the load current will shift to the body diode first. The high dv/dt of the phase node voltage will charge the qfw嘉泰姆

miller capaci-tor through the low-side MOSFET driver sinking current path. This results in much less switchingqfw嘉泰姆

 loss of the low-side MOSFETs. The duty cycle is often very small in high battery voltage applications, and the qfw嘉泰姆

low-side MOSFET will conduct most of the switching cycle; therefore, when using smaller RDS(ON) of the low-side MOSFET, the con-verter can reduce power loss. The gate charge for this MOSFET is usually the qfw嘉泰姆

secondary consideration. The high-side MOSFET does not have this zero voltage switch- ing condition;qfw嘉泰姆

 in addition, because  it conducts for less time compared to the low-side MOSFET, the switching qfw嘉泰姆

loss tends to be dominant. Priority  should be given to the MOSFETs with less gate charge, so qfw嘉泰姆

that both the gate driver loss and switching loss  will be minimized.qfw嘉泰姆

The selection of the N-channel power MOSFETs are determined by the R DS(ON), reversingqfw嘉泰姆

 transfer capaci-tance (CRSS) and maximum output current requirement. The losses in the qfw嘉泰姆

MOSFETs have two components:conduction loss and transition loss. For the high-side and qfw嘉泰姆

low-side MOSFETs, the losses are approximately given by the following equations:qfw嘉泰姆

Phigh-side = IOUT (1+ TC)(RDS(ON))D + (0.5)( IOUT)(VIN)( tSW)FSW
Plow-side = IOUT (1+ TC)(RDS(ON))(1-D)
Where I is the load current OUT
TC is the temperature dependency of RDS(ON)
FSW is the switching frequency
tSW is the switching interval
D is the duty cycle
Note that both MOSFETs have conduction losses while the high-side MOSFET includes an additional qfw嘉泰姆

transition loss.The switching interval, tSW, is the function of the reverse transfer capacitance CRSS. qfw嘉泰姆

The (1+TC) term is a factor in the temperature dependency of the RDS(ON) and can be extracted qfw嘉泰姆

from the “RDS(ON) vs. Temperature” curve of the power MOSFET.
Layout Consideration
In any high switching frequency converter, a correct layout is important to ensure proper operation qfw嘉泰姆

of the regulator.With power devices switching at higher frequency, the resulting current transient will qfw嘉泰姆

cause voltage spike across the interconnecting impedance and parasitic circuit elements. As an example,qfw嘉泰姆

 consider the turn-off transition of the PWM MOSFET. Before turn-off condition, the MOSFET is carryingqfw嘉泰姆

 the full load current. During turn-off,current stops flowing in the MOSFET and is freewheeling by the qfw嘉泰姆

low side MOSFET and parasitic diode. Any parasitic inductance of the circuit generates a large voltage qfw嘉泰姆

spike during the switching interval. In general, using short and wide printed circuit traces shouldqfw嘉泰姆

 minimize interconnect-ing impedances and the magnitude of voltage spike.
Besides, signal and power grounds are to be kept sepa-rating and finally combined using ground qfw嘉泰姆

plane construc-tion or single point grounding. The best tie-point between the signal ground and the qfw嘉泰姆

power ground is at the nega-tive side of the output capacitor on each channel, where there is less qfw嘉泰姆

noise. Noisy traces beneath the IC are not recommended. Below is a checklist for your layout:
· Keep the switching nodes (UGATE, LGATE, BOOT,and PHASE) away from sensitive small signal qfw嘉泰姆

nodes since these nodes are fast moving signals.Therefore, keep traces to these nodes as short as
possible and there should be no other weak signal traces in parallel with theses traces on any layer.
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Layout Consideration (Cont.)
· The signals going through theses traces have both high dv/dt and high di/dt with high peak qfw嘉泰姆

charging and discharging current. The traces from the gate drivers to the MOSFETs (UGATE and qfw嘉泰姆

LGATE) should be short and wide.
· Place the source of the high-side MOSFET and the drain of the low-side MOSFET as close as qfw嘉泰姆

possible.Minimizing the impedance with wide layout plane be-tween the two pads reduces the qfw嘉泰姆

voltage bounce of the node. In addition, the large layout plane between the drain of the qfw嘉泰姆

MOSFETs (VIN and PHASE nodes) can get better heat sinking.qfw嘉泰姆

The GND is the current sensing circuit reference ground and also the power ground of the qfw嘉泰姆

LGATE low-side MOSFET. On the other hand, the GND trace should be a separate trace andqfw嘉泰姆

 independently go to the source of the low-side MOSFET. Besides, the cur-rent sense resistor qfw嘉泰姆

should be close to OCSET pin to avoid parasitic capacitor effect and noise coupling.qfw嘉泰姆

· Decoupling capacitors, the resistor-divider, and boot capacitor should be close to their pins. qfw嘉泰姆

(For example,place the decoupling ceramic capacitor close to the drain of the high-side MOSFETqfw嘉泰姆

 as close as possible.)
· The input bulk capacitors should be close to the drain of the high-side MOSFET, and the outputqfw嘉泰姆

 bulk capaci-tors should be close to the loads. The input capaci-tor’s ground should be close to theqfw嘉泰姆

 grounds of the output capacitors and low-side MOSFET.
· Locate the resistor-divider close to the FB pin to mini-mize the high impedance trace. In addition, qfw嘉泰姆

FB pin traces can’t be close to the switching signal traces (UGATE, LGATE, BOOT, and PHASE).qfw嘉泰姆

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