目录54o嘉泰姆

1.产品概述                       2.产品特点54o嘉泰姆
3.应用范围                       4.下载产品资料PDF文档 54o嘉泰姆
5.产品封装图                     6.电路原理图                   54o嘉泰姆
7.功能概述                        8.相关产品54o嘉泰姆

一,产品概述(General Description)  54o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                                                         54o嘉泰姆

产品特点(Features)54o嘉泰姆

High Input Voltages Range from 3V to 28V Input Power54o嘉泰姆
Provide Adjustable Output Voltage from 0.75V to54o嘉泰姆
5.5V +1% Accuracy over Temperature54o嘉泰姆
Integrated MOSFET Drivers and Bootstrap Forward P-CH MOSFET54o嘉泰姆
Low Quiescent Current (200μA)54o嘉泰姆
Excellent Line and Load Transient Responses54o嘉泰姆
PFM Mode for Increased Light Load Efficiency54o嘉泰姆
Constant On-Time Controller Scheme54o嘉泰姆
- Switching Frequency Compensation for PWM Mode54o嘉泰姆
- Adjustable Switching Frequency from 100kHz to54o嘉泰姆
550kHz in PWM Mode with DC Output Current54o嘉泰姆
S3 and S5 Pins Control The Device in S0, S3 or S4/S5 State54o嘉泰姆
Power Good Monitoring54o嘉泰姆
Extra Droop Voltage Control Function with54o嘉泰姆
Adjustable Current Setting54o嘉泰姆
70% Under-Voltage Protection (UVP)54o嘉泰姆
125% Over-Voltage Protection (OVP)54o嘉泰姆
Adjustable Current-Limit Protection54o嘉泰姆
- Using Sense Low-Side MOSFET’s RDS(ON)54o嘉泰姆
TQFN-20 3mmx3mm Thin package54o嘉泰姆
Lead Free Available (RoHS Compliant)54o嘉泰姆
+1.5A LDO Section (VTT)54o嘉泰姆
Sourcing or Sinking Current up to 1.5A54o嘉泰姆
Fast Transient Response for Output Voltage54o嘉泰姆
Output Ceramic Capacitors Support at least 10μF MLCC54o嘉泰姆
VTT and VTTREF Track at Half the VDDQSNS by internal divider54o嘉泰姆
+20mV Accuracy for VTT and VTTREF54o嘉泰姆
Independent Over-Current Limit (OCL)54o嘉泰姆
Thermal Shutdown Protection54o嘉泰姆
三,应用范围 (Applications)54o嘉泰姆

DDR2, and DDR3 Memory Power Supplies54o嘉泰姆
SSTL-2 SSTL-18 and HSTL Termination54o嘉泰姆
四.下载产品资料PDF文档 54o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！54o嘉泰姆

 54o嘉泰姆

五,产品封装图 (Package)54o嘉泰姆

54o嘉泰姆
六.电路原理图54o嘉泰姆

54o嘉泰姆

七,功能概述54o嘉泰姆

Soft- Start (cont.)54o嘉泰姆

During soft-start stage before the PGOOD pin is ready,54o嘉泰姆
the under voltage protection is prohibited. The over volt-54o嘉泰姆
age and current limit protection functions are enabled. If54o嘉泰姆
the output capacitor has residue voltage before startup,54o嘉泰姆
both low-side and high-side MOSFETs are in off-state54o嘉泰姆
until the internal digital soft start voltage equal the inter-54o嘉泰姆
nal feedback voltage. This will ensure the output voltage54o嘉泰姆
starts from its existing voltage level.54o嘉泰姆
The VTT LDO part monitors the output current, both sourc-54o嘉泰姆
ing and sinking current, and limits the maximum output54o嘉泰姆
current to prevent damages during current overload or54o嘉泰姆
short circuit (shorted from VTT to GND or VLDOIN)54o嘉泰姆
conditions.54o嘉泰姆
The VTT LDO provides a soft-start function, using the54o嘉泰姆
constant current to charge the output capacitor that gives54o嘉泰姆
a rapid and linear output voltage rise. If the load current is54o嘉泰姆
above the current limit start-up, the VTT cannot start54o嘉泰姆
successfully.CXSD62121A CXSD62121B CXSD62121 has an independent counter for each output,54o嘉泰姆
but the PGOOD signal indicates only the status of VDDQ54o嘉泰姆
and does not indicate VTT power good externally.54o嘉泰姆
Power-Good Output (PGOOD)54o嘉泰姆
PGOOD is an open-drain output and the PGOOD com-54o嘉泰姆
parator continuously monitors the output voltage. PGOOD54o嘉泰姆
is actively held low in shutdown, and standby. When PWM54o嘉泰姆
converter’s output voltage is greater than 95% of its tar-54o嘉泰姆
get value, the internal open-drain device will be pulled54o嘉泰姆
low. After 63μs debounce time, the PGOOD goes high.54o嘉泰姆
The PGOOD goes low if VVDDQ output is 10% below or54o嘉泰姆
above its nominal regulation point.54o嘉泰姆
Under Voltage Protection54o嘉泰姆
In the process of operation, if a short-circuit occurs, the54o嘉泰姆
output voltage will drop quickly. When load current is big-54o嘉泰姆
ger than current limit threshold value, the output voltage54o嘉泰姆
will fall out of the required regulation range. The under-54o嘉泰姆
voltage continually monitors the setting output voltage54o嘉泰姆
after 2ms of PWM operations to ensure startup. If a load54o嘉泰姆
step is strong enough to pull the output voltage lower54o嘉泰姆
than the under voltage threshold (70% of normal output54o嘉泰姆
voltage), CXSD62121A CXSD62121B CXSD62121 shuts down the output gradually and54o嘉泰姆
latches off both high and low side MOSFETs.54o嘉泰姆
Over Voltage Protection (OVP)54o嘉泰姆
The feedback voltage should increase over 125% of the54o嘉泰姆
reference voltage due to the high-side MOSFET failure or54o嘉泰姆
for other reasons, and the over voltage protection com-54o嘉泰姆
parator designed with a 1.5μs noise filter will force the54o嘉泰姆
low-side MOSFET gate driver to be high. This action ac-54o嘉泰姆
tively pulls down the output voltage and eventually at-54o嘉泰姆
tempts to blow the battery fuse.54o嘉泰姆
When the OVP occurs, the PGOOD pin will pull down and54o嘉泰姆
latch-off the converter. This OVP scheme only clamps the54o嘉泰姆
voltage overshoot, and does not invert the output voltage54o嘉泰姆
when otherwise activated with a continuously high output54o嘉泰姆
from low-side MOSFET driver. It’s a common problem for54o嘉泰姆
OVP schemes with a latch. Once an over-voltage fault54o嘉泰姆
condition is set, toggling VCC power-on-reset signal can54o嘉泰姆
only reset it.54o嘉泰姆
PWM Converter Current Limit54o嘉泰姆
The current-limit circuit employs a unique “valley” current54o嘉泰姆
sensing algorithm (Figure 2). CS pin should be con-54o嘉泰姆
nected to VCC through the trip voltage-setting resistor,54o嘉泰姆
RCS. CS terminal sinks 5mA current, ICS, and the current54o嘉泰姆
limit threshold is set to the voltage across the RCS. The54o嘉泰姆
voltage between or CS_GND pin and PHASE pin moni-54o嘉泰姆
tors the inductor current so that PHASE pin should be54o嘉泰姆
connected to the drain terminal of the low side MOSFET.54o嘉泰姆
PGND is used as the positive current sensing node so54o嘉泰姆
that PGND should be connected to the proper current54o嘉泰姆
sensing device, i.e. the sense resistor or the source ter-54o嘉泰姆
minal of the low side MOSFET.54o嘉泰姆
If the magnitude of the current-sense signal is above the54o嘉泰姆
current-limit threshold, the PWM is not allowed to initiate54o嘉泰姆
a new cycle. The actual peak current is greater than the54o嘉泰姆
current-limit threshold by an amount equal to the induc-54o嘉泰姆
tor ripple current. Therefore, the exact current- limit char-54o嘉泰姆
acteristic and maximum load capability are a function of54o嘉泰姆
the sense resistance, inductor value, and input voltage.54o嘉泰姆
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