目录b29嘉泰姆

1.产品概述                       2.产品特点b29嘉泰姆
3.应用范围                       4.下载产品资料PDF文档 b29嘉泰姆
5.产品封装图                     6.电路原理图                   b29嘉泰姆
7.功能概述                        8.相关产品b29嘉泰姆

一,产品概述(General Description)  b29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                                                         b29嘉泰姆

产品特点(Features)b29嘉泰姆

High Input Voltages Range from 3V to 28V Input Powerb29嘉泰姆
Provide Adjustable Output Voltage from 0.75V tob29嘉泰姆
5.5V +1% Accuracy over Temperatureb29嘉泰姆
Integrated MOSFET Drivers and Bootstrap Forward P-CH MOSFETb29嘉泰姆
Low Quiescent Current (200μA)b29嘉泰姆
Excellent Line and Load Transient Responsesb29嘉泰姆
PFM Mode for Increased Light Load Efficiencyb29嘉泰姆
Constant On-Time Controller Schemeb29嘉泰姆
- Switching Frequency Compensation for PWM Modeb29嘉泰姆
- Adjustable Switching Frequency from 100kHz tob29嘉泰姆
550kHz in PWM Mode with DC Output Currentb29嘉泰姆
S3 and S5 Pins Control The Device in S0, S3 or S4/S5 Stateb29嘉泰姆
Power Good Monitoringb29嘉泰姆
Extra Droop Voltage Control Function withb29嘉泰姆
Adjustable Current Settingb29嘉泰姆
70% Under-Voltage Protection (UVP)b29嘉泰姆
125% Over-Voltage Protection (OVP)b29嘉泰姆
Adjustable Current-Limit Protectionb29嘉泰姆
- Using Sense Low-Side MOSFET’s RDS(ON)b29嘉泰姆
TQFN-20 3mmx3mm Thin packageb29嘉泰姆
Lead Free Available (RoHS Compliant)b29嘉泰姆
+1.5A LDO Section (VTT)b29嘉泰姆
Sourcing or Sinking Current up to 1.5Ab29嘉泰姆
Fast Transient Response for Output Voltageb29嘉泰姆
Output Ceramic Capacitors Support at least 10μF MLCCb29嘉泰姆
VTT and VTTREF Track at Half the VDDQSNS by internal dividerb29嘉泰姆
+20mV Accuracy for VTT and VTTREFb29嘉泰姆
Independent Over-Current Limit (OCL)b29嘉泰姆
Thermal Shutdown Protectionb29嘉泰姆
三,应用范围 (Applications)b29嘉泰姆

DDR2, and DDR3 Memory Power Suppliesb29嘉泰姆
SSTL-2 SSTL-18 and HSTL Terminationb29嘉泰姆
四.下载产品资料PDF文档 b29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！b29嘉泰姆

 b29嘉泰姆

五,产品封装图 (Package)b29嘉泰姆

b29嘉泰姆
六.电路原理图b29嘉泰姆

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七,功能概述b29嘉泰姆

Soft- Start (cont.)b29嘉泰姆

During soft-start stage before the PGOOD pin is ready,b29嘉泰姆
the under voltage protection is prohibited. The over volt-b29嘉泰姆
age and current limit protection functions are enabled. Ifb29嘉泰姆
the output capacitor has residue voltage before startup,b29嘉泰姆
both low-side and high-side MOSFETs are in off-stateb29嘉泰姆
until the internal digital soft start voltage equal the inter-b29嘉泰姆
nal feedback voltage. This will ensure the output voltageb29嘉泰姆
starts from its existing voltage level.b29嘉泰姆
The VTT LDO part monitors the output current, both sourc-b29嘉泰姆
ing and sinking current, and limits the maximum outputb29嘉泰姆
current to prevent damages during current overload orb29嘉泰姆
short circuit (shorted from VTT to GND or VLDOIN)b29嘉泰姆
conditions.b29嘉泰姆
The VTT LDO provides a soft-start function, using theb29嘉泰姆
constant current to charge the output capacitor that givesb29嘉泰姆
a rapid and linear output voltage rise. If the load current isb29嘉泰姆
above the current limit start-up, the VTT cannot startb29嘉泰姆
successfully.CXSD62121A CXSD62121B CXSD62121 has an independent counter for each output,b29嘉泰姆
but the PGOOD signal indicates only the status of VDDQb29嘉泰姆
and does not indicate VTT power good externally.b29嘉泰姆
Power-Good Output (PGOOD)b29嘉泰姆
PGOOD is an open-drain output and the PGOOD com-b29嘉泰姆
parator continuously monitors the output voltage. PGOODb29嘉泰姆
is actively held low in shutdown, and standby. When PWMb29嘉泰姆
converter’s output voltage is greater than 95% of its tar-b29嘉泰姆
get value, the internal open-drain device will be pulledb29嘉泰姆
low. After 63μs debounce time, the PGOOD goes high.b29嘉泰姆
The PGOOD goes low if VVDDQ output is 10% below orb29嘉泰姆
above its nominal regulation point.b29嘉泰姆
Under Voltage Protectionb29嘉泰姆
In the process of operation, if a short-circuit occurs, theb29嘉泰姆
output voltage will drop quickly. When load current is big-b29嘉泰姆
ger than current limit threshold value, the output voltageb29嘉泰姆
will fall out of the required regulation range. The under-b29嘉泰姆
voltage continually monitors the setting output voltageb29嘉泰姆
after 2ms of PWM operations to ensure startup. If a loadb29嘉泰姆
step is strong enough to pull the output voltage lowerb29嘉泰姆
than the under voltage threshold (70% of normal outputb29嘉泰姆
voltage), CXSD62121A CXSD62121B CXSD62121 shuts down the output gradually andb29嘉泰姆
latches off both high and low side MOSFETs.b29嘉泰姆
Over Voltage Protection (OVP)b29嘉泰姆
The feedback voltage should increase over 125% of theb29嘉泰姆
reference voltage due to the high-side MOSFET failure orb29嘉泰姆
for other reasons, and the over voltage protection com-b29嘉泰姆
parator designed with a 1.5μs noise filter will force theb29嘉泰姆
low-side MOSFET gate driver to be high. This action ac-b29嘉泰姆
tively pulls down the output voltage and eventually at-b29嘉泰姆
tempts to blow the battery fuse.b29嘉泰姆
When the OVP occurs, the PGOOD pin will pull down andb29嘉泰姆
latch-off the converter. This OVP scheme only clamps theb29嘉泰姆
voltage overshoot, and does not invert the output voltageb29嘉泰姆
when otherwise activated with a continuously high outputb29嘉泰姆
from low-side MOSFET driver. It’s a common problem forb29嘉泰姆
OVP schemes with a latch. Once an over-voltage faultb29嘉泰姆
condition is set, toggling VCC power-on-reset signal canb29嘉泰姆
only reset it.b29嘉泰姆
PWM Converter Current Limitb29嘉泰姆
The current-limit circuit employs a unique “valley” currentb29嘉泰姆
sensing algorithm (Figure 2). CS pin should be con-b29嘉泰姆
nected to VCC through the trip voltage-setting resistor,b29嘉泰姆
RCS. CS terminal sinks 5mA current, ICS, and the currentb29嘉泰姆
limit threshold is set to the voltage across the RCS. Theb29嘉泰姆
voltage between or CS_GND pin and PHASE pin moni-b29嘉泰姆
tors the inductor current so that PHASE pin should beb29嘉泰姆
connected to the drain terminal of the low side MOSFET.b29嘉泰姆
PGND is used as the positive current sensing node sob29嘉泰姆
that PGND should be connected to the proper currentb29嘉泰姆
sensing device, i.e. the sense resistor or the source ter-b29嘉泰姆
minal of the low side MOSFET.b29嘉泰姆
If the magnitude of the current-sense signal is above theb29嘉泰姆
current-limit threshold, the PWM is not allowed to initiateb29嘉泰姆
a new cycle. The actual peak current is greater than theb29嘉泰姆
current-limit threshold by an amount equal to the induc-b29嘉泰姆
tor ripple current. Therefore, the exact current- limit char-b29嘉泰姆
acteristic and maximum load capability are a function ofb29嘉泰姆
the sense resistance, inductor value, and input voltage.b29嘉泰姆
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