目录0tO嘉泰姆

1.产品概述                       2.产品特点0tO嘉泰姆
3.应用范围                       4.下载产品资料PDF文档 0tO嘉泰姆
5.产品封装图                     6.电路原理图                   0tO嘉泰姆
7.功能概述                        8.相关产品0tO嘉泰姆

一,产品概述(General Description)  0tO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                                                         0tO嘉泰姆

产品特点(Features)0tO嘉泰姆

High Input Voltages Range from 3V to 28V Input Power0tO嘉泰姆
Provide Adjustable Output Voltage from 0.75V to0tO嘉泰姆
5.5V +1% Accuracy over Temperature0tO嘉泰姆
Integrated MOSFET Drivers and Bootstrap Forward P-CH MOSFET0tO嘉泰姆
Low Quiescent Current (200μA)0tO嘉泰姆
Excellent Line and Load Transient Responses0tO嘉泰姆
PFM Mode for Increased Light Load Efficiency0tO嘉泰姆
Constant On-Time Controller Scheme0tO嘉泰姆
- Switching Frequency Compensation for PWM Mode0tO嘉泰姆
- Adjustable Switching Frequency from 100kHz to0tO嘉泰姆
550kHz in PWM Mode with DC Output Current0tO嘉泰姆
S3 and S5 Pins Control The Device in S0, S3 or S4/S5 State0tO嘉泰姆
Power Good Monitoring0tO嘉泰姆
Extra Droop Voltage Control Function with0tO嘉泰姆
Adjustable Current Setting0tO嘉泰姆
70% Under-Voltage Protection (UVP)0tO嘉泰姆
125% Over-Voltage Protection (OVP)0tO嘉泰姆
Adjustable Current-Limit Protection0tO嘉泰姆
- Using Sense Low-Side MOSFET’s RDS(ON)0tO嘉泰姆
TQFN-20 3mmx3mm Thin package0tO嘉泰姆
Lead Free Available (RoHS Compliant)0tO嘉泰姆
+1.5A LDO Section (VTT)0tO嘉泰姆
Sourcing or Sinking Current up to 1.5A0tO嘉泰姆
Fast Transient Response for Output Voltage0tO嘉泰姆
Output Ceramic Capacitors Support at least 10μF MLCC0tO嘉泰姆
VTT and VTTREF Track at Half the VDDQSNS by internal divider0tO嘉泰姆
+20mV Accuracy for VTT and VTTREF0tO嘉泰姆
Independent Over-Current Limit (OCL)0tO嘉泰姆
Thermal Shutdown Protection0tO嘉泰姆
三,应用范围 (Applications)0tO嘉泰姆

DDR2, and DDR3 Memory Power Supplies0tO嘉泰姆
SSTL-2 SSTL-18 and HSTL Termination0tO嘉泰姆
四.下载产品资料PDF文档 0tO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！0tO嘉泰姆

 0tO嘉泰姆

五,产品封装图 (Package)0tO嘉泰姆

0tO嘉泰姆
六.电路原理图0tO嘉泰姆

0tO嘉泰姆

七,功能概述0tO嘉泰姆

Soft- Start (cont.)0tO嘉泰姆

During soft-start stage before the PGOOD pin is ready,0tO嘉泰姆
the under voltage protection is prohibited. The over volt-0tO嘉泰姆
age and current limit protection functions are enabled. If0tO嘉泰姆
the output capacitor has residue voltage before startup,0tO嘉泰姆
both low-side and high-side MOSFETs are in off-state0tO嘉泰姆
until the internal digital soft start voltage equal the inter-0tO嘉泰姆
nal feedback voltage. This will ensure the output voltage0tO嘉泰姆
starts from its existing voltage level.0tO嘉泰姆
The VTT LDO part monitors the output current, both sourc-0tO嘉泰姆
ing and sinking current, and limits the maximum output0tO嘉泰姆
current to prevent damages during current overload or0tO嘉泰姆
short circuit (shorted from VTT to GND or VLDOIN)0tO嘉泰姆
conditions.0tO嘉泰姆
The VTT LDO provides a soft-start function, using the0tO嘉泰姆
constant current to charge the output capacitor that gives0tO嘉泰姆
a rapid and linear output voltage rise. If the load current is0tO嘉泰姆
above the current limit start-up, the VTT cannot start0tO嘉泰姆
successfully.CXSD62121A CXSD62121B CXSD62121 has an independent counter for each output,0tO嘉泰姆
but the PGOOD signal indicates only the status of VDDQ0tO嘉泰姆
and does not indicate VTT power good externally.0tO嘉泰姆
Power-Good Output (PGOOD)0tO嘉泰姆
PGOOD is an open-drain output and the PGOOD com-0tO嘉泰姆
parator continuously monitors the output voltage. PGOOD0tO嘉泰姆
is actively held low in shutdown, and standby. When PWM0tO嘉泰姆
converter’s output voltage is greater than 95% of its tar-0tO嘉泰姆
get value, the internal open-drain device will be pulled0tO嘉泰姆
low. After 63μs debounce time, the PGOOD goes high.0tO嘉泰姆
The PGOOD goes low if VVDDQ output is 10% below or0tO嘉泰姆
above its nominal regulation point.0tO嘉泰姆
Under Voltage Protection0tO嘉泰姆
In the process of operation, if a short-circuit occurs, the0tO嘉泰姆
output voltage will drop quickly. When load current is big-0tO嘉泰姆
ger than current limit threshold value, the output voltage0tO嘉泰姆
will fall out of the required regulation range. The under-0tO嘉泰姆
voltage continually monitors the setting output voltage0tO嘉泰姆
after 2ms of PWM operations to ensure startup. If a load0tO嘉泰姆
step is strong enough to pull the output voltage lower0tO嘉泰姆
than the under voltage threshold (70% of normal output0tO嘉泰姆
voltage), CXSD62121A CXSD62121B CXSD62121 shuts down the output gradually and0tO嘉泰姆
latches off both high and low side MOSFETs.0tO嘉泰姆
Over Voltage Protection (OVP)0tO嘉泰姆
The feedback voltage should increase over 125% of the0tO嘉泰姆
reference voltage due to the high-side MOSFET failure or0tO嘉泰姆
for other reasons, and the over voltage protection com-0tO嘉泰姆
parator designed with a 1.5μs noise filter will force the0tO嘉泰姆
low-side MOSFET gate driver to be high. This action ac-0tO嘉泰姆
tively pulls down the output voltage and eventually at-0tO嘉泰姆
tempts to blow the battery fuse.0tO嘉泰姆
When the OVP occurs, the PGOOD pin will pull down and0tO嘉泰姆
latch-off the converter. This OVP scheme only clamps the0tO嘉泰姆
voltage overshoot, and does not invert the output voltage0tO嘉泰姆
when otherwise activated with a continuously high output0tO嘉泰姆
from low-side MOSFET driver. It’s a common problem for0tO嘉泰姆
OVP schemes with a latch. Once an over-voltage fault0tO嘉泰姆
condition is set, toggling VCC power-on-reset signal can0tO嘉泰姆
only reset it.0tO嘉泰姆
PWM Converter Current Limit0tO嘉泰姆
The current-limit circuit employs a unique “valley” current0tO嘉泰姆
sensing algorithm (Figure 2). CS pin should be con-0tO嘉泰姆
nected to VCC through the trip voltage-setting resistor,0tO嘉泰姆
RCS. CS terminal sinks 5mA current, ICS, and the current0tO嘉泰姆
limit threshold is set to the voltage across the RCS. The0tO嘉泰姆
voltage between or CS_GND pin and PHASE pin moni-0tO嘉泰姆
tors the inductor current so that PHASE pin should be0tO嘉泰姆
connected to the drain terminal of the low side MOSFET.0tO嘉泰姆
PGND is used as the positive current sensing node so0tO嘉泰姆
that PGND should be connected to the proper current0tO嘉泰姆
sensing device, i.e. the sense resistor or the source ter-0tO嘉泰姆
minal of the low side MOSFET.0tO嘉泰姆
If the magnitude of the current-sense signal is above the0tO嘉泰姆
current-limit threshold, the PWM is not allowed to initiate0tO嘉泰姆
a new cycle. The actual peak current is greater than the0tO嘉泰姆
current-limit threshold by an amount equal to the induc-0tO嘉泰姆
tor ripple current. Therefore, the exact current- limit char-0tO嘉泰姆
acteristic and maximum load capability are a function of0tO嘉泰姆
the sense resistance, inductor value, and input voltage.0tO嘉泰姆
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