Preliminary Datasheet CXT-STA4919 (Cissoid) - 8

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CXT-STA4919 – Preliminary Datasheet External resistances calculation rules CEB input
R1 and R2 values should be computed as CEB input pin internal circuit is depicted in follows: Figure 13. R1+ R2 VOUT = R2 V 9 . 0
700 KΩ Vin
VIN VOUT
Vout CEB
CEB
Cin
FB
Cout VF = 3V CXT-STA4919
GND R1+R2 value should be lower than 200kΩ Figure 13 to limit the impact of the FB input leakage current. For VOUT = 0.9V, VOUT signal CEB threshold is set by the threshold of can be tied directly to FB pin. the transistor T1 (value between 1.2 and 2V).
Input and output capacitance
It is expected that CEB pin will be driven CXT-STA4919 requires an output capaci- by a controller and so that the CEB control tor connected between VOUT and GND to signal voltage range will be typically be- stabilize the internal control loop. The out- tween 0V and [3.3V-5V]; in this case, the put capacitance value must be between 1 leakage current through the CEB pin will 3 µF and 10 µF; ESR (equivalent series re- µA typ. over the whole temperature range. sistance) value should be between 0.01Ω and 1Ω. Would the application use a larger voltage Higher capacitor values offer improved swing to control the CEB pin, system de- behaviour in case of fast and high ampli- signers should take into account that CEB tude load transient. pin will present an additional equivalent resistance of about 700KΩ. There is no explicit requirement on the value of the input capacitance. Its size
Current limit
mainly depends on system aspects (im- pedance of the power source, distance In case the load connected to CXT- between power source and CXT- STA4919 would demand more than 50 mA STA4919, amount and speed of the load current, the internal current limiter circuit transients ...). CISSOID recommends the will limit the maximum current delivered by use of a 1 µF input capacitance. CXT-STA4919 to 200mA (typical) whatev- er the output voltage. If the output current exceeds the recom- mended 50mA and depending on the con- ditions (dropout, junction-2-air thermal re- sistance), the internal thermal protection could get activated and CXT-STA4919 would then switch between 2 modes: - Thermal protection active; no out- put current - Thermal protection not active; out- put current internally limited. In case of short-circuit, both current limiter and thermal protection will be activated and will protect the device. PUBLIC
1-May-19 Doc. PDS-181975 V1.0 WWW.CISSOID.COM
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