目录xqq嘉泰姆

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

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

产品特点(Features)xqq嘉泰姆

High Input Voltages Range from 3V to 28V Input Powerxqq嘉泰姆
Provide Adjustable Output Voltage from 0.75V toxqq嘉泰姆
5.5V +1% Accuracy over Temperaturexqq嘉泰姆
Integrated MOSFET Drivers and Bootstrap Forward P-CH MOSFETxqq嘉泰姆
Low Quiescent Current (200μA)xqq嘉泰姆
Excellent Line and Load Transient Responsesxqq嘉泰姆
PFM Mode for Increased Light Load Efficiencyxqq嘉泰姆
Constant On-Time Controller Schemexqq嘉泰姆
- Switching Frequency Compensation for PWM Modexqq嘉泰姆
- Adjustable Switching Frequency from 100kHz toxqq嘉泰姆
550kHz in PWM Mode with DC Output Currentxqq嘉泰姆
S3 and S5 Pins Control The Device in S0, S3 or S4/S5 Statexqq嘉泰姆
Power Good Monitoringxqq嘉泰姆
Extra Droop Voltage Control Function withxqq嘉泰姆
Adjustable Current Settingxqq嘉泰姆
70% Under-Voltage Protection (UVP)xqq嘉泰姆
125% Over-Voltage Protection (OVP)xqq嘉泰姆
Adjustable Current-Limit Protectionxqq嘉泰姆
- Using Sense Low-Side MOSFET’s RDS(ON)xqq嘉泰姆
TQFN-20 3mmx3mm Thin packagexqq嘉泰姆
Lead Free Available (RoHS Compliant)xqq嘉泰姆
+1.5A LDO Section (VTT)xqq嘉泰姆
Sourcing or Sinking Current up to 1.5Axqq嘉泰姆
Fast Transient Response for Output Voltagexqq嘉泰姆
Output Ceramic Capacitors Support at least 10μF MLCCxqq嘉泰姆
VTT and VTTREF Track at Half the VDDQSNS by internal dividerxqq嘉泰姆
+20mV Accuracy for VTT and VTTREFxqq嘉泰姆
Independent Over-Current Limit (OCL)xqq嘉泰姆
Thermal Shutdown Protectionxqq嘉泰姆
三,应用范围 (Applications)xqq嘉泰姆

DDR2, and DDR3 Memory Power Suppliesxqq嘉泰姆
SSTL-2 SSTL-18 and HSTL Terminationxqq嘉泰姆
四.下载产品资料PDF文档 xqq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！xqq嘉泰姆

 xqq嘉泰姆

五,产品封装图 (Package)xqq嘉泰姆

xqq嘉泰姆
六.电路原理图xqq嘉泰姆

xqq嘉泰姆

七,功能概述xqq嘉泰姆

Soft- Start (cont.)xqq嘉泰姆

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