sc1470 Semtech Corporation, sc1470 Datasheet
sc1470
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sc1470 Summary of contents
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... POWER MANAGEMENT Description The SC1470 is a single output, constant on-time synchronous-buck PWM controller intended for use in notebook computers and other battery operated portable devices. Features include high efficiency and fast dynamic response with no minimum on time. The excellent transient response means that SC1470 based solutions will require less output capacitance than competing fixed frequency converters ...
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... D > SC1470 ...
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... SC1470 2 ° ° ° ...
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... SC1470 2 ° ° ° ...
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... SC1470 ...
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... TON (2) VOUT (3) 1.5V REF FB (5) X3 PGD (6) VSSA (7) 2005 Semtech Corp TON OFF CONTROL LOGIC PWM TOFF OC ZERO FAULT UV MONITOR REF + 10% REF - 10% REF - 30% Figure 1 - SC1470 Block Diagram 6 SC1470 tplhDH BST (14) DH (13 (12) ISENSE ILIM (11) VDDP (10) DL (9) LO PGND (8) www.semtech.com ...
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... Enable & Psave The EN/PSV pin enables the supply. When EN/PSV is tied to VCCA the controller is enabled and power save will also be enabled. If PSAVE is enabled, the SC1470 PSAVE comparator will look for the inductor current to cross zero on eight consecutive switching cycles by comparing the phase node (LX) to PGND. Once observed, the controller will enter power save and turn off the low side MOSFET when the current crosses zero ...
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... Figure 2: Setting The Output Voltage Current Limit Circuit Current limiting of the SC1470 can be accomplished in two ways. The on-state resistance of the low-side MOSFET can be used as the current sensing element or sense resistors in series with the low-side source can be used if greater accuracy is desired. R efficient and less expensive ...
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... PGND through the inductor and bottom MOSFET). In this case, when the bottom MOSFET is turned on, the phase node, LX, will be higher than PGND initially. The SC1470 monitors the voltage at LX, and greater than a set threshold voltage of 125mV (nom.) the bottom MOSFET is turned off. The device then waits for approximately 2.5µ ...
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... DC accuracy. The use of 1% feedback resistors contribute 1%. If tighter DC accuracy is required use 0.1% feedback resistors. The on pulse in the SC1470 is calculated to give a pseudo fixed frequency. Nevertheless, some frequency variation with line and load can be expected. This variation changes the output ripple voltage. Because constant on regulators regulate to the valley of the output ripple, ½ ...
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... We will select a value of 12.5m P-P design, which would be achieved by using two 25m output capacitors in parallel. Note that for constant-on converters there is a minimum ) A ESR requirement for stability which can be calculated as ( MIN ) follows: 11 SC1470 = 7.1A (MIN) ) and transient ESR ESR_ST(MAX) ): ERR ERR Ohms ) I ...
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... I term. = 20.0k and For our example: TOP C = 610µF. OUT(MIN) We will select 440µF, using two 220µF, 25m capacitors in parallel. For smaller load release overshoot, 12 SC1470 based upon the selected C FB TOP R V BOT RIPPLE _ VBAT ( MIN ...
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... Q = 60nC 266kHz Ohms VBAT (MIN) VBST (MIN 1.2/8 = 0.15 (MIN) = 7.76k gives us: ILIM P 5 1100 088 and SC1470 I VDDP I VCCA VDDP f VBST (V) ON condition (since (MIN VBAT +VDDP = 13V (MIN 150 ...
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... POWER MANAGEMENT As can be seen, the heating effects due to internal power dissipation are practically negligible, thus requiring no special consideration thermally during layout. 2005 Semtech Corp. 14 SC1470 www.semtech.com ...
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... PGD VSSA PGND 1uF 0603 N OTES ( not required but aids k eeping VSSA s eparate f rom PGN ept where des ired in lay out. Figure 4: Reference Design 15 SC1470 VBAT 2n2/50V 0u1/25V 10u/25V 0402 0603 1210 L1 2u2 C6 ...
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... C5 R3 20k0 4 VCCA 56p 0402 0402 PGD R7 7 VSSA C8 14k3 C10 0402 1nF 1uF 0402 0603 Figure 5: Components Connected to VSSA Figure 6: Example VSSA 0.020” Trace 16 SC1470 5VSUS SC1470 14 BST ILIM 10 VDDP PGND 1uF 0603 www.semtech.com ...
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... PGD VSSA PGND VSSA VBAT 2n2/50V 0u1/25V 10u/25V 0402 0603 1210 L1 2u2 (2) 220u/25m 7343 0402 Figure 8: Power Section and Input Loop 17 SC1470 VOUT C14 R12 0R (2) 220u/25m 220u/25m 7343 7343 0402 VOUT C7 + 220u/25m 7343 www.semtech.com ...
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... BST is also a noisy node and should be kept as short as possible. 4) Connect PGND pin on the chip directly to the VDDP decoupling capacitor and then drop vias directly to the ground plane. 2005 Semtech Corp. resistor at the bottom of the output capacitor to connect to VSSA. BAT 18 SC1470 and ground at high frequencies, www.semtech.com ...
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... POWER MANAGEMENT U1 1 EN/PSV 2 TON 3 VOUT 4 VCCA PGD 7 VSSA Figure 10: Connecting the Control and Power Sections 2005 Semtech Corp. SC470 14 Q1 BST IRF7811AV 7k87 11 ILIM 0402 10 Q2 VDDP FDS6676S PGND 19 SC1470 L1 2u2 www.semtech.com ...
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... Switching Frequency (Continuous Conduction Mode) vs. Output Current vs. Input Voltage 400 350 300 250 200 150 100 SC1470 BAT V = 20V BAT (A) OUT V = 20V BAT BAT ...
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... Trace 4: load current, 5A/div Timebase: 40µs/div. Trace 1: 1.2V, 20mV/div., AC coupled Trace 2: LX, 10V/div Trace 3: not connected Trace 4: load current, 5A/div Timebase: 10µs/div. Trace 1: 1.2V, 50mV/div., AC coupled Trace 2: LX, 10V/div Trace 3: not connected Trace 4: load current, 5A/div Timebase: 10µs/div. 21 SC1470 www.semtech.com ...
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... Trace 4: load current, 5A/div Timebase: 40µs/div. Trace 1: 1.2V, 20mV/div., AC coupled Trace 2: LX, 10V/div Trace 3: not connected Trace 4: load current, 5A/div Timebase: 10µs/div. Trace 1: 1.2V, 50mV/div., AC coupled Trace 2: LX, 10V/div Trace 3: not connected Trace 4: load current, 5A/div Timebase: 10µs/div. 22 SC1470 www.semtech.com ...
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... Startup (CCM), EN/PSV 0V to Floating Please refer to Figure 4 on Page 15 for test schematic 2005 Semtech Corp. Trace 1: 1.2V, 0.5V/div. Trace 2: LX, 10V/div Trace 3: EN/PSV, 5V/div Trace 4: PGD, 5V/div. Timebase: 1ms/div. Trace 1: 1.2V, 0.5V/div. Trace 2: LX, 10V/div Trace 3: EN/PSV, 5V/div Trace 4: PGD, 5V/div. Timebase: 1ms/div. 23 SC1470 www.semtech.com ...
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... GAGE bxN PLANE bbb C A-B D 0.25 DETAIL A SEE DETAIL SIDE VIEW AND - DETERMINED AT DATUM PLANE -H- 24 SC1470 Bottom Mark xxxxxx = Wafer Lot Number xx = Assembly Lot Number MILLIMETERS MAX MIN NOM MAX - - .047 1.20 - .006 0.05 0.15 - .042 0.80 1.05 - .012 0.19 0.30 - ...
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... CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. Contact Information Phone: (805)498-2111 FAX (805)498-3804 2005 Semtech Corp. DIMENSIONS DIM INCHES (.222 .161 P .026 .016 Y .061 Z .283 Y Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 25 SC1470 MILLIMETERS (5.65) 4.10 0.65 0.40 1.55 7.20 www.semtech.com ...