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目录jww嘉泰姆

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

一,产品概述(General Description)  jww嘉泰姆

    The CXSD62121A CXSD62121B CXSD62121 integrates a synchronous buck PWM con-troller to generate VDDQ, a sourcing and sinking LDO linear regulator to generate VTT. It offers the lowest total solution cost in system where space is at a premium.  The CXSD62121A CXSD62121B CXSD62121 provides excellent transient response and accurate DC voltage output in either PFM or PWM Mode.In Pulse Frequency Mode (PFM), the CXSD62121A CXSD62121B CXSD62121 provides very high efficiency over light to heavy loads with loading-modulated switching frequencies. On TQFN-20 Package,the Forced PWM Mode works nearly at constant frequency for low-noise requirements.  The CXSD62121A CXSD62121B CXSD62121 is equipped with accurate current-limit,output under-voltage, and output over-voltage protections.A Power-On- Reset function monitors the voltage on VCC prevents wrong operation during power on. Droop func-tion is allowed to adjust output voltage during light load period.The LDO is designed to provide a regulated voltage with bi-directional output current for DDR-SDRAM termination.The device integrates two power transistors to source or sink current up to 1.5A. It also incorporates current-limit and thermal shutdown protection.The output voltage of LDO tracks the voltage at VREF pin.An internal resistor divider is used to provide a half volt-age of VREF for VTTREF and VTT Voltage. The VTT output voltage is only requiring 20μF of ceramic output capaci tance for stability and fast transient response. The S3 and S5 pins provide the sleep state for VTT (S3 state)and suspend state (S4/S5 state) for device, when S5 and S3 are both pulled low the device provides the soft-off for VTT and VTTREF                                                         jww嘉泰姆

产品特点(Features)jww嘉泰姆

High Input Voltages Range from 3V to 28V Input Powerjww嘉泰姆
Provide Adjustable Output Voltage from 0.75V tojww嘉泰姆
5.5V +1% Accuracy over Temperaturejww嘉泰姆
Integrated MOSFET Drivers and Bootstrap Forward P-CH MOSFETjww嘉泰姆
Low Quiescent Current (200μA)jww嘉泰姆
Excellent Line and Load Transient Responsesjww嘉泰姆
PFM Mode for Increased Light Load Efficiencyjww嘉泰姆
Constant On-Time Controller Schemejww嘉泰姆
- Switching Frequency Compensation for PWM Modejww嘉泰姆
- Adjustable Switching Frequency from 100kHz tojww嘉泰姆
550kHz in PWM Mode with DC Output Currentjww嘉泰姆
S3 and S5 Pins Control The Device in S0, S3 or S4/S5 Statejww嘉泰姆
Power Good Monitoringjww嘉泰姆
Extra Droop Voltage Control Function withjww嘉泰姆
Adjustable Current Settingjww嘉泰姆
70% Under-Voltage Protection (UVP)jww嘉泰姆
125% Over-Voltage Protection (OVP)jww嘉泰姆
Adjustable Current-Limit Protectionjww嘉泰姆
- Using Sense Low-Side MOSFET’s RDS(ON)jww嘉泰姆
TQFN-20 3mmx3mm Thin packagejww嘉泰姆
Lead Free Available (RoHS Compliant)jww嘉泰姆
+1.5A LDO Section (VTT)jww嘉泰姆
Sourcing or Sinking Current up to 1.5Ajww嘉泰姆
Fast Transient Response for Output Voltagejww嘉泰姆
Output Ceramic Capacitors Support at least 10μF MLCCjww嘉泰姆
VTT and VTTREF Track at Half the VDDQSNS by internal dividerjww嘉泰姆
+20mV Accuracy for VTT and VTTREFjww嘉泰姆
Independent Over-Current Limit (OCL)jww嘉泰姆
Thermal Shutdown Protectionjww嘉泰姆
三,应用范围 (Applications)jww嘉泰姆

DDR2, and DDR3 Memory Power Suppliesjww嘉泰姆
SSTL-2 SSTL-18 and HSTL Terminationjww嘉泰姆
四.下载产品资料PDF文档 jww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！jww嘉泰姆

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五,产品封装图 (Package)jww嘉泰姆

jww嘉泰姆
六.电路原理图jww嘉泰姆

jww嘉泰姆

七,功能概述jww嘉泰姆

Soft- Start (cont.)jww嘉泰姆

During soft-start stage before the PGOOD pin is ready,jww嘉泰姆
the under voltage protection is prohibited. The over volt-jww嘉泰姆
age and current limit protection functions are enabled. Ifjww嘉泰姆
the output capacitor has residue voltage before startup,jww嘉泰姆
both low-side and high-side MOSFETs are in off-statejww嘉泰姆
until the internal digital soft start voltage equal the inter-jww嘉泰姆
nal feedback voltage. This will ensure the output voltagejww嘉泰姆
starts from its existing voltage level.jww嘉泰姆
The VTT LDO part monitors the output current, both sourc-jww嘉泰姆
ing and sinking current, and limits the maximum outputjww嘉泰姆
current to prevent damages during current overload orjww嘉泰姆
short circuit (shorted from VTT to GND or VLDOIN)jww嘉泰姆
conditions.jww嘉泰姆
The VTT LDO provides a soft-start function, using thejww嘉泰姆
constant current to charge the output capacitor that givesjww嘉泰姆
a rapid and linear output voltage rise. If the load current isjww嘉泰姆
above the current limit start-up, the VTT cannot startjww嘉泰姆
successfully.CXSD62121A CXSD62121B CXSD62121 has an independent counter for each output,jww嘉泰姆
but the PGOOD signal indicates only the status of VDDQjww嘉泰姆
and does not indicate VTT power good externally.jww嘉泰姆
Power-Good Output (PGOOD)jww嘉泰姆
PGOOD is an open-drain output and the PGOOD com-jww嘉泰姆
parator continuously monitors the output voltage. PGOODjww嘉泰姆
is actively held low in shutdown, and standby. When PWMjww嘉泰姆
converter’s output voltage is greater than 95% of its tar-jww嘉泰姆
get value, the internal open-drain device will be pulledjww嘉泰姆
low. After 63μs debounce time, the PGOOD goes high.jww嘉泰姆
The PGOOD goes low if VVDDQ output is 10% below orjww嘉泰姆
above its nominal regulation point.jww嘉泰姆
Under Voltage Protectionjww嘉泰姆
In the process of operation, if a short-circuit occurs, thejww嘉泰姆
output voltage will drop quickly. When load current is big-jww嘉泰姆
ger than current limit threshold value, the output voltagejww嘉泰姆
will fall out of the required regulation range. The under-jww嘉泰姆
voltage continually monitors the setting output voltagejww嘉泰姆
after 2ms of PWM operations to ensure startup. If a loadjww嘉泰姆
step is strong enough to pull the output voltage lowerjww嘉泰姆
than the under voltage threshold (70% of normal outputjww嘉泰姆
voltage), CXSD62121A CXSD62121B CXSD62121 shuts down the output gradually andjww嘉泰姆
latches off both high and low side MOSFETs.jww嘉泰姆
Over Voltage Protection (OVP)jww嘉泰姆
The feedback voltage should increase over 125% of thejww嘉泰姆
reference voltage due to the high-side MOSFET failure orjww嘉泰姆
for other reasons, and the over voltage protection com-jww嘉泰姆
parator designed with a 1.5μs noise filter will force thejww嘉泰姆
low-side MOSFET gate driver to be high. This action ac-jww嘉泰姆
tively pulls down the output voltage and eventually at-jww嘉泰姆
tempts to blow the battery fuse.jww嘉泰姆
When the OVP occurs, the PGOOD pin will pull down andjww嘉泰姆
latch-off the converter. This OVP scheme only clamps thejww嘉泰姆
voltage overshoot, and does not invert the output voltagejww嘉泰姆
when otherwise activated with a continuously high outputjww嘉泰姆
from low-side MOSFET driver. It’s a common problem forjww嘉泰姆
OVP schemes with a latch. Once an over-voltage faultjww嘉泰姆
condition is set, toggling VCC power-on-reset signal canjww嘉泰姆
only reset it.jww嘉泰姆
PWM Converter Current Limitjww嘉泰姆
The current-limit circuit employs a unique “valley” currentjww嘉泰姆
sensing algorithm (Figure 2). CS pin should be con-jww嘉泰姆
nected to VCC through the trip voltage-setting resistor,jww嘉泰姆
RCS. CS terminal sinks 5mA current, ICS, and the currentjww嘉泰姆
limit threshold is set to the voltage across the RCS. Thejww嘉泰姆
voltage between or CS_GND pin and PHASE pin moni-jww嘉泰姆
tors the inductor current so that PHASE pin should bejww嘉泰姆
connected to the drain terminal of the low side MOSFET.jww嘉泰姆
PGND is used as the positive current sensing node sojww嘉泰姆
that PGND should be connected to the proper currentjww嘉泰姆
sensing device, i.e. the sense resistor or the source ter-jww嘉泰姆
minal of the low side MOSFET.jww嘉泰姆
If the magnitude of the current-sense signal is above thejww嘉泰姆
current-limit threshold, the PWM is not allowed to initiatejww嘉泰姆
a new cycle. The actual peak current is greater than thejww嘉泰姆
current-limit threshold by an amount equal to the induc-jww嘉泰姆
tor ripple current. Therefore, the exact current- limit char-jww嘉泰姆
acteristic and maximum load capability are a function ofjww嘉泰姆
the sense resistance, inductor value, and input voltage.jww嘉泰姆
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