lm5027asqx National Semiconductor Corporation, lm5027asqx Datasheet
lm5027asqx
Related parts for lm5027asqx
lm5027asqx Summary of contents
Page 1
... Additional fea- tures include Line Under Voltage Lockout (UVLO), separate soft-start of main and synchronous rectifier outputs, a timer for hiccup mode current limiting, a precision reference, and thermal shutdown. Typical Application Circuit © 2010 National Semiconductor Corporation LM5027A Features ■ Voltage-Mode control ■ ...
Page 2
... Connection Diagrams 20-Lead eTSSOP Ordering Information Order Number Package Type LM5027AMH eTSSOP-20 LM5027AMHX eTSSOP-20 LM5027ASQ LLP-24 LM5027ASQX LLP-24 www.national.com 30111902 NSC Package Drawing Package Marking MXA20A LM5027AMH MXA20A LM5027AMH SQA24B LM5027A SQA24B LM5027A 2 30111990 24-Lead LLP Supplied As 73 units per Rail ...
Page 3
Pin Descriptions Pin Name Description 1 VIN Input voltage source 2 RAMP Feed-forward modulation ramp 3 TIME3 Overlap delay 3 4 TIME2 Overlap delay 2 5 TIME1 Overlap delay 1 6 AGND Analog ground 7 RT Oscillator frequency control and ...
Page 4
Pin Name Description 17 RES Restart timer 18 SSSR Soft-start for synchronous rectifier output. 19 OTP Over-Temperature Protection 20 UVLO Line under-voltage lockout EP Exposed pad, underside of package Note: The pin numbers shown are only for the eTSSOP package. ...
Page 5
Absolute Maximum Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN to GND VCC to GND UVLO to GND All other inputs to GND COMP Input Current COMP, REF ...
Page 6
Symbol Parameter OSCILLATOR Frequency1 Sync Threshold Sync Pulse Width PWM COMPARATORS Delay to Output COMP to PWM Offset Duty Cycle Maximum CURRENT LIMIT RESTART (RES Pin) RES Threshold Charge Source Current Level 1 V Charge Source Current Level 2 4.0V ...
Page 7
Symbol Parameter OUTSR GATE DRIVER VOL OUTSR Low-state Output Voltage VOH OUTSR High-state Output Voltage OUTSR Rise Time OUTSR High Side Fall Time IOHH Peak OUTSR Source Current IOLH Peak OUTSR Sink Current OUTPUT TIMING CONTROL T1 Delay Leading Range ...
Page 8
Typical Performance Characteristics Efficiency VCC vs. I Oscillator Frequency vs R www.national.com 30111940 CC 30111925 Resistor T 30111927 8 VCC and V vs. VIN REF 30111924 V vs. I REF REF 30111926 Oscillator Frequency vs Temperature 30111928 ...
Page 9
Time1 Delay vs R (kΩ) TIME1 30111929 Time3 Delay vs R (kΩ) TIME3 30111931 Time2 Delay vs Temperature R = 28.7 kΩ TIME2 30111933 Time2 Delay vs R TIME2 Time1 Delay vs Temperature R = 33.2 kΩ TIME1 Time3 Delay ...
Page 10
SS Pin Current vs Temperature RES Pin Charging Current Level 1 vs Temperature www.national.com SSSR Pin Charging Current vs Temperature 30111935 30111937 10 30111936 ...
Page 11
Block Diagram FIGURE 1. Simplified Block Diagram 11 30111903 www.national.com ...
Page 12
Detailed Operating Description The LM5027A PWM controller contains all the features nec- essary to implement power converters utilizing the Active Clamp Reset technique with synchronous rectification. The device is configured to control a P-Channel clamp switch. With the active clamp ...
Page 13
RES pin to gradually increase. If the RES voltage reaches the 1.0V threshold, the following restart se- quence occurs (also see Figure 2). • The SS and SSSR capacitors are fully discharged. • The RES 20 ...
Page 14
Soft-Start The soft-start circuit allows the regulator to gradually increase its output voltage until the steady state operating point is reached; thereby reducing start-up stresses and surge cur- rents. When bias power is supplied to the LM5027A, the SS pin ...
Page 15
FIGURE 4. Soft-Start/Soft-Stop Timing FIGURE 5. Soft-Start and Drive Enable 15 30111906 30111907 www.national.com ...
Page 16
External Over-Temperature Protection An external set-point voltage divider between the REF, OTP, and AGND pins, as shown in Figure plement over-temperature protection shutdown. Typically a NTC thermistor is installed as the lower device of the voltage divider. The divider must ...
Page 17
Fault/Event Vcc UVLO UVLO<0.4V >6.2V - 2.0V<UVLO >6.2V - >0.4V SS< 1V >6.2V >2.0V SSSR <2.0V >6.2V >2.0V OTP >6.2V >2.0V <1.25V PWM Comparators The pulse width modulator (PWM) comparator compares the voltage ramp signal at the RAMP pin to ...
Page 18
Volt-Second Clamp An external resistor (R ) and a capacitor (C FF between the VIN, RAMP and AGND pins is required to create a saw-tooth modulation ramp signal as shown in slope of the RAMP will vary in proportion to ...
Page 19
Gate Drive Outputs The LM5027A contains three unique gate drivers. OUTA, the primary switch driver, is designed to drive the gate Channel MOSFET and is capable of sourcing and sinking a peak current of 2A. The active ...
Page 20
For Applications > 100V For applications where the system input voltage (V ceeds 100V, VIN can be powered from an external start-up regulator as shown in Figure 11. Connecting the VIN and VCC pins together allows the LM5027A to be ...
Page 21
FIGURE 12. UVLO Circuit with Shutdown Control Oscillator The oscillator frequency is generally selected in conjunction with the system magnetic components and any other aspects of the system which may be affected by the frequency. The R resistor selection equation ...
Page 22
Current Sense The CS pin receives an input signal representative of the transformer primary current, either from a current sense transformer or from a resistor in series with the source of the primary switch, as shown in Figure 14 cases ...
Page 23
Soft-Start The capacitor on the SS pin determines the time required for the output duty cycle to increase from zero to its final value for regulation. The minimum acceptable time is dependent on the output capacitance and the response of ...
Page 24
The hiccup mode provides the periodic cool-down time for the power converter in the event of a sustained overload or short Printed Circuit Board Layout The LM5027A Current Sense and PWM comparators are very fast and respond to short duration ...
Page 25
25 www.national.com ...
Page 26
Physical Dimensions www.national.com inches (millimeters) unless otherwise noted 20 Lead eTSSOP NS Package Number MXA20A 24 Lead LLP NS Package Number SQA24B 26 ...
Page 27
Notes 27 www.national.com ...
Page 28
... National Semiconductor and the National Semiconductor logo are registered trademarks of National Semiconductor Corporation. All other brand or product names may be trademarks or registered trademarks of their respective holders. ...