目录pYy嘉泰姆

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

一,产品概述(General Description)  pYy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                                                         pYy嘉泰姆

产品特点(Features)pYy嘉泰姆

High Input Voltages Range from 3V to 28V Input PowerpYy嘉泰姆
Provide Adjustable Output Voltage from 0.75V topYy嘉泰姆
5.5V +1% Accuracy over TemperaturepYy嘉泰姆
Integrated MOSFET Drivers and Bootstrap Forward P-CH MOSFETpYy嘉泰姆
Low Quiescent Current (200μA)pYy嘉泰姆
Excellent Line and Load Transient ResponsespYy嘉泰姆
PFM Mode for Increased Light Load EfficiencypYy嘉泰姆
Constant On-Time Controller SchemepYy嘉泰姆
- Switching Frequency Compensation for PWM ModepYy嘉泰姆
- Adjustable Switching Frequency from 100kHz topYy嘉泰姆
550kHz in PWM Mode with DC Output CurrentpYy嘉泰姆
S3 and S5 Pins Control The Device in S0, S3 or S4/S5 StatepYy嘉泰姆
Power Good MonitoringpYy嘉泰姆
Extra Droop Voltage Control Function withpYy嘉泰姆
Adjustable Current SettingpYy嘉泰姆
70% Under-Voltage Protection (UVP)pYy嘉泰姆
125% Over-Voltage Protection (OVP)pYy嘉泰姆
Adjustable Current-Limit ProtectionpYy嘉泰姆
- Using Sense Low-Side MOSFET’s RDS(ON)pYy嘉泰姆
TQFN-20 3mmx3mm Thin packagepYy嘉泰姆
Lead Free Available (RoHS Compliant)pYy嘉泰姆
+1.5A LDO Section (VTT)pYy嘉泰姆
Sourcing or Sinking Current up to 1.5ApYy嘉泰姆
Fast Transient Response for Output VoltagepYy嘉泰姆
Output Ceramic Capacitors Support at least 10μF MLCCpYy嘉泰姆
VTT and VTTREF Track at Half the VDDQSNS by internal dividerpYy嘉泰姆
+20mV Accuracy for VTT and VTTREFpYy嘉泰姆
Independent Over-Current Limit (OCL)pYy嘉泰姆
Thermal Shutdown ProtectionpYy嘉泰姆
三,应用范围 (Applications)pYy嘉泰姆

DDR2, and DDR3 Memory Power SuppliespYy嘉泰姆
SSTL-2 SSTL-18 and HSTL TerminationpYy嘉泰姆
四.下载产品资料PDF文档 pYy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！pYy嘉泰姆

 pYy嘉泰姆

五,产品封装图 (Package)pYy嘉泰姆

pYy嘉泰姆
六.电路原理图pYy嘉泰姆

pYy嘉泰姆

七,功能概述pYy嘉泰姆

Soft- Start (cont.)pYy嘉泰姆

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