LM3753SQX National Semiconductor, LM3753SQX Datasheet
LM3753SQX
Available stocks
Related parts for LM3753SQX
LM3753SQX Summary of contents
Page 1
... System accuracy better than 1% ■ 0.6V to 3.6V output voltage range ■ Switching frequency from 200 kHz to 1 MHz Simplified Application © 2009 National Semiconductor Corporation LM3753/54 ■ Phase current sharing ±12% max over temperature ■ Integrated 4.35V ±2.3% LDO ■ Inductor DCR or sense resistor current sensing ■ ...
Page 2
... Connection Diagram Ordering Information TRACK/SS Order Number function LM3753SQ TRACK LM3753SQX TRACK LM3754SQ SS Pre-Bias Protection LM3754SQX SS Pre-Bias Protection www.national.com Top View 32-Lead LLP Package Type NSC Package Drawing LLP-32 SQA32A LLP-32 SQA32A LLP-32 SQA32A LLP-32 SQA32A 2 30091903 Supplied As 1000 Units / Reel ...
Page 3
Pin Descriptions Pin Number Pin Name Description 1 HG2 Gate drive of the high-side N-channel MOSFET for Phase 2. 2 SW2 Switching node of the power stage of Phase 2. 3 LG2 Gate drive of the low-side N-channel MOSFETs for ...
Page 4
Pin Number Pin Name Description 23 TRACK Tracking Input. Connect the TRACK pins of all of the controllers in the system together. Wire the (LM3753) TRACK pin to the external TRACK control signal. Tracking is always enabled on power-up, shutdown ...
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 SGND, PGND SGND to PGND VCC and VDD to VIN VDD to PGND PGOOD, FAULT to SGND VCC, EN, SS, TRACK, SYNC, CS1, CS2, CSM, ...
Page 6
Symbol Parameter VCC V VCC Linear Regulator Output VCC Voltage I VCC Input Current from External VCC Supply I VCC Input Shutdown Current from VCC-SD External Supply I VCC Output Current Limit VCC-LIM V VCC UVLO Thresholds VCC-EN V VCC ...
Page 7
Symbol Parameter EN V HIGH Level Input Voltage EN-H V LOW Level Input Voltage EN Threshold EN- Threshold Hysteresis EN-HYS I EN Input Bias Current EN Reference, Feedback & Error Amplifier: FB, COMP V FB Voltage ...
Page 8
Symbol Parameter f 3dB Bandwidth, CS1(2) to PWM BW-CS COMPARATOR Input I ILIM Source Current ILIM-SOURCE V Current Limit Threshold Voltage CL V − V ILIM CS1(2) t Current Limit Comparator D-CL Propagation Delay t Master or Slave Fast Current ...
Page 9
Symbol Parameter Divider Ratio to Set RATIO PH VCC Phase Number I PH Bias Current PH Φ HG1 to HG2 Phase Shift for HG1- 12-Phase Modes Φ HG1 to HG2 Phase ...
Page 10
Symbol Parameter Gate Drivers I HG1 and HG2 Peak Source PK-HG-SOURCE Current R HG1 and HG2 Source Resistance V HG-SOURCE I HG1 and HG2 Peak Sink Current PK-HG-SINK R HG1 and HG2 Sink Resistance HG-SINK I LG1 and LG2 Peak ...
Page 11
Typical Performance Characteristics System Accuracy Deviation REF V vs Temperature REF OUT 30091904 30091905 30091906 Temperature SW 30091907 FRQ SW 30091908 Load Step (High Slew) 30091909 www.national.com ...
Page 12
LM3754 (SS) Startup from 0V LM3754 (SS) Pre-Biased Output Startup LM3753 (TRACK) Startup www.national.com 30091910 Repeated Over-Voltage Conditions 30091911 Over-Current Fault (Soft Short) 30091912 12 Over-Voltage Fault 30091913 30091914 30091915 ...
Page 13
Block Diagram 13 www.national.com ...
Page 14
Functional Description GENERAL The LM3753 and LM3754 are two-phase voltage-mode step- down (buck) switching regulator controllers. From one to six LM3753/54 controllers can be connected together to control from two to twelve phases ( 10, ...
Page 15
FIGURE 2. Power Connections Using a System 5V Rail FIGURE 3. Power Connections for V UNDER-VOLTAGE LOCKOUTS and ENABLE The LM3753/54 controller has internal under-voltage lockout (UVLO) detection on the VCC and VDD supplies. The under- voltage lockout on VIN ...
Page 16
By means of the closed loop regulation through the switching stage, FB will be regulated to TRACK. When TRACK is below VREF, the LM3753 will control FB both up and down to follow TRACK. When TRACK is above VREF, ...
Page 17
The restart after fault process for the LM3754 is the same as the initial startup process pulled low and the system will go through a full soft-start cycle. Switching will resume when SS crosses above FB. The restart ...
Page 18
Master feedback divider at SGND. The COMP pin of each Slave is connected to its corresponding VDIF pin. This provides sufficient buffering of the master COMP signal for the internal summing of the current averaging circuit. OSCILLATOR ...
Page 19
COMP to provide the duty cycle adjustment for phase-to- phase current sharing. Application Information NUMBER of PHASES The number of phases can be calculated by dividing the max- imum output load current by 25A. Therefore a 120A load requirement ...
Page 20
In order to track properly, the external power supply voltage must be higher than the LM3753 output voltage. SOFT-START (LM3754) To avoid current limit during startup, the soft-start time t should be substantially longer than the time required to charge ...
Page 21
FIGURE 11. Multi-Phase Output Voltage Ripple Based on the normalized single phase ripple, the worst case multi-phase output voltage ripple can be approximated as: ΔV (N) = Δ Where N is the number of phases. The ...
Page 22
By defining the maximum input voltage ripple, the minimum requirement for the input capacitance can be calculated as: For multi-phase operation, the general equation for the input capacitor rms current is approximated as: This is valid for D < 1 ...
Page 23
... MOSFET R due to self heating. Alternatively, DS(on) the 1.3 can be ignored and the R DS(on) mated using the R vs. Temperature curves in the MOS- DS(on) FET datasheets. The gate charge loss results from the current driving the gate capacitance of the power MOSFETs, and is approximated as ...
Page 24
Choosing C DCR = 440 nH / (0.15 μF x 0.52 mΩ) = 5.64 kΩ. R DCR Using a standard value of 5.90 kΩ, the average current is calculated as 203 μA from: through R DCR I ...
Page 25
The control loop is comprised of two parts. The first is the power stage, which consists of the duty cycle modulator, cur- rent sharing circuit, output filter and load. The second part is the error amplifier, which is a voltage ...
Page 26
FIGURE 14. Power Stage Gain FIGURE 15. Power Stage Phase Assuming a pole at the origin, the simplified equation for the error amplifier transfer function can be written in terms of the mid-band gain as: Where: www.national.com In general, the ...
Page 27
For output capacitors with very low ESR, if the target crossover frequency is more than 10 times the filter pole fre- quency, bandwidth limiting of the error amplifier may occur. See the Comprehensive Equations section to incorporate the error amplifier ...
Page 28
FIGURE 18. Control Loop Gain FIGURE 19. Control Loop Phase For the small-signal analysis assumed that the control voltage at the COMP pin is dc. In practice, the output ripple voltage is amplified by the error amplifier gain ...
Page 29
If possible, the SNSP and SNSM traces should be shielded from the switch node by ground planes. SGND and PGND CONNECTIONS Good layout techniques include a dedicated ground plane, usually on an internal ...
Page 30
If ω < ω , calculate the optimal crossover frequency from www.national.com Using this method, the maximum phase boost is achieved at the optimal crossover frequency. In either case, the upper limit for f C switching frequency. 30 ...
Page 31
Typical Application All controllers in the system are the same part. The Master and Slave are differentiated by how they are connected in the system. FIGURE 20. Typical Application 31 30091902 www.national.com ...
Page 32
Design Examples www.national.com 32 ...
Page 33
33 www.national.com ...
Page 34
www.national.com 34 ...
Page 35
35 www.national.com ...
Page 36
Physical Dimensions www.national.com inches (millimeters) unless otherwise noted 32-Lead LLP Package NS Package Number SQA32A 36 ...
Page 37
Notes 37 www.national.com ...
Page 38
... For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Amplifiers www.national.com/amplifiers Audio www.national.com/audio Clock and Timing www.national.com/timing Data Converters www.national.com/adc Interface www.national.com/interface LVDS www.national.com/lvds Power Management www.national.com/power Switching Regulators www.national.com/switchers LDOs www.national.com/ldo LED Lighting www ...