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NCP3488 MOSFET Driver with Dual Outputs for Synchronous Buck Converters
The NCP3488 is a single Phase 12 V MOSFET gate driver optimized to drive the gates of both high-side and low-side power MOSFETs in a synchronous buck converter. The high-side and low-side driver is capable of driving a 3000 pF load with a 25 ns propagation delay and a 20 ns transition time. With a wide operating voltage range, high or low side MOSFET gate drive voltage can be optimized for the best efficiency. Internal adaptive nonoverlap circuitry further reduces switching losses by preventing simultaneous conduction of both MOSFETs. The floating top driver design can accommodate VBST voltages as high as 30 V, with transient voltages as high as 35 V. Both gate outputs can be driven low by applying a low logic level to the Output Disable (OD) pin. An Undervoltage Lockout function ensures that both driver outputs are low when the supply voltage is low, and a Thermal Shutdown function provides the IC with overtemperature protection.
Features http://onsemi.com MARKING DIAGRAMS
8 8 1 A L Y W G SO-8 D SUFFIX CASE 751 N3488 ALYW G
1
= Assembly Location = Wafer Lot = Year = Work Week = Pb-Free Package
PIN CONNECTIONS
BST IN OD VCC 1 8 DRVH SWN PGND DRVL
* Thermal Shutdown for System Protection * Internal Pulldown Resistor Suppresses Transient Turn On of Either * * * * * * * * *
MOSFET Anti Cross-Conduction Protection Circuitry Floating Top Driver Accommodates Boost Voltages of up to 30 V One Input Signal Controls Both the Upper and Lower Gate Outputs Output Disable Control Turns Off Both MOSFETs Complies with VRM10.x and VRM11.x Specifications Undervoltage Lockout Thermal Shutdown Thermally Enhanced Package Available This is a Pb-Free Device
ORDERING INFORMATION
Device NCP3488DR2G Package SO-8 (Pb-Free) Shipping 2500 Tape & Reel
For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specification Brochure, BRD8011/D.
(c) Semiconductor Components Industries, LLC, 2006
May, 2006 - Rev. 1
1
Publication Order Number: NCP3488/D
NCP3488
OD 3 V CC TSD UVLO IN 2 8 DRVH 1 BST
FALLING EDGE DELAY FALLING EDGE DELAY START STOP NON-OVERLAP TIMERS
MONITOR 7 MONITOR SWN
MIN DRVL OFF TIMER
4 5 6
V CC DRVL PGND
Figure 1. Block Diagram
PIN DESCRIPTION
Pin No. 1 Symbol BST Description Upper MOSFET Floating Bootstrap Supply. A capacitor connected between BST and SW pins holds this bootstrap voltage for the high-side MOSFET as it is switched. The recommended capacitor value is between 100 nF and 1.0 mF. An external diode is required with the NCP3488. Logic-Level Input. This pin has primary control of the drive outputs. Output Disable. When low, normal operation is disabled forcing DRVH and DRVL low. Input Supply. A 1.0 mF ceramic capacitor should be connected from this pin to PGND. Output drive for the lower MOSFET. Power Ground. Should be closely connected to the source of the lower MOSFET. Switch Node. Connect to the source of the upper MOSFET. Output drive for the upper MOSFET.
2 3 4 5 6 7 8
IN OD VCC DRVL PGND SWN DRVH
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NCP3488
MAXIMUM RATINGS
Rating Operating Ambient Temperature, TA Operating Junction Temperature, TJ (Note 1) Package Thermal Resistance: SO-8 Junction-to-Case, RqJC Junction-to-Ambient, RqJA (2-Layer Board) Storage Temperature Range, TS Lead Temperature Soldering (10 sec): Reflow (SMD styles only) JEDEC Moisture Sensitivity Level Pb-Free (Note 3) (260 peak profile) Value 0 to 85 0 to 150 45 123 -65 to 150 260 peak 1 Unit C C C/W C/W C C -
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect device reliability. 1. Internally limited by thermal shutdown, 150C min. 2. 2 layer board, 1 in2 Cu, 1 oz thickness. 3. 60-180 seconds minimum above 237C. NOTE: This device is ESD sensitive. Use standard ESD precautions when handling.
MAXIMUM RATINGS
Pin Symbol VCC BST Pin Name Main Supply Voltage Input Bootstrap Supply Voltage Input VMAX 15 V 30 V wrt/PGND 35 V v 50 ns wrt/PGND 15 V wrt/SW 30 V BST + 0.3 V 35 V v 50 ns wrt/PGND 15 V wrt/SW VCC + 0.3 V VCC + 0.3 V VCC + 0.3 V 0V VMIN -0.3 V -0.3 V wrt/SW
SW DRVH
Switching Node (Bootstrap Supply Return) High-Side Driver Output
-1.0 V DC -10 V< 200 ns -0.3 V wrt/SW
DRVL IN OD PGND NOTE:
Low-Side Driver Output DRVH and DRVL Control Input Output Disable Ground
-0.3 V DC -2.0 V < 200 ns -0.3 V -0.3 V 0V
All voltages are with respect to PGND except where noted.
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NCP3488
ELECTRICAL CHARACTERISTICS (Note 4) (VCC = 12 V, TA = 0C to +85C, TJ = 0C to +125C unless otherwise noted.)
Characteristic Supply Supply Voltage Range Supply Current OD Input Input Voltage High Input Voltage Low Hysteresis Input Current Propagation Delay Time (Note 5) PWM Input Input Voltage High Input Voltage Low Hysteresis Input Current High-Side Driver Output Resistance, Sourcing Current Output Resistance, Sinking Current Transition Times (Note 5) Propagation Delay (Notes 5 & 6) Low-Side Driver Output Resistance, Sourcing Current Output Resistance, Sinking Current Timeout Delay Transition Times Propagation Delay Undervoltage Lockout UVLO Startup UVLO Shutdown Hysteresis Thermal Shutdown Over Temperature Protection Hysteresis 4. 5. 6. 7. - (Note 7) (Note 7) 150 - 170 20 - - C C - - - - - - 3.7 3.2 0.3 3.9 3.5 0.4 4.4 3.9 0.7 V V V - - - trDRVL tfDRVL tpdhDRVL tpdlDRVL VCC = 12 V (Note 7) VCC - VSW = 12 V (Note 7) DRVH-SW = 0 CLOAD = 3.0 nF (See Figure 3) (See Figure 3) - - - - - - - 1.8 1.0 85 16 11 30 20 - - - - - - - W W ns ns ns ns ns - - trDRVH tfDRVH tpdhDRVH tpdlDRVH VBST - VSW = 12 V (Note 7) VBST - VSW = 12 V (Note 7) VBST - VSW = 12 V, CLOAD = 3.0 nF (See Figure 3) VBST - VSW = 12 V - - - - - - 1.8 1.0 16 11 30 25 - - - - - - W W ns ns ns ns - - - - - - - No internal pull-up or pull-down resistors 2.0 - - -1.0 - - 500 - - 0.8 - +1.0 V V mV mA - - - - tpdlOD tpdhOD - - - No internal pull-up or pull-down resistors - 2.0 - - -1.0 30 30 - - 500 - 50 50 - 0.8 - +1.0 60 60 V V mV mA ns ns VCC ISYS - BST = 12 V, IN = 0 V 4.6 - - 2.0 13.2 6.0 V mA Symbol Condition Min Typ Max Unit
All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC). AC specifications are guaranteed by characterization, but not production tested. For propagation delays, "tpdh'' refers to the specified signal going high; "tpdl'' refers to it going low. GBD: Guaranteed by design; not tested in production. Specifications subject to change without notice.
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NCP3488
OD tpdlOD 90% DRVH or DRVL 10% tpdhOD
Figure 2. Output Disable Timing Diagram
IN
tpdlDRVL
tfDRVL 90% 10% tpdhDRVH trDRVH 90% tpdlDRVH 90% 2V 10% tpdhDRVL tfDRVH 10% trDRVL
DRVL
90% 2V
DRVH-SW 10%
SW
Figure 3. Nonoverlap Timing Diagram
APPLICATIONS INFORMATION
Theory of Operation High-Side Driver
The NCP3488 is a single phase MOSFET driver designed for driving two N-channel MOSFETs in a synchronous buck converter topology. The NCP3488 will operate from 5 V or 12 V, but it has been optimized for high current multi-phase buck regulators that convert 12 Volt rail directly to the core voltage required by complex logic chips. A single PWM input signal is all that is required to properly drive the high-side and the low-side MOSFETs. Each driver is capable of driving a 3.3 nF load at frequencies up to 500 kHz.
Low-Side Driver
The low-side driver is designed to drive a ground-referenced low RDS(on) N-Channel MOSFET. The voltage rail for the low-side driver is internally connected to the VCC supply and PGND.
The high-side driver is designed to drive a floating low RDS(on) N-channel MOSFET. The gate voltage for the high side driver is developed by a bootstrap circuit referenced to Switch Node (SW) pin. The bootstrap circuit is comprised of an external diode, and an external bootstrap capacitor. When the NCP3488 is starting up, the SW pin is at ground, so the bootstrap capacitor will charge up to VCC through the bootstrap diode See Figure 4. When the PWM input goes high, the high-side driver will begin to turn on the high-side MOSFET using the stored charge of the bootstrap capacitor. As the high-side MOSFET turns on, the SW pin will rise. When the high-side MOSFET is fully on, the switch node will be at 12 volts, and the BST pin will be at 12 volts plus the charge of the bootstrap capacitor (approaching 24 volts). The bootstrap capacitor is recharged when the switch node goes low during the next cycle.
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NCP3488
Safety Timer and Overlap Protection Circuit Input Pins
It is very important that MOSFETs in a synchronous buck regulator do not both conduct at the same time. Excessive shoot-through or cross conduction can damage the MOSFETs, and even a small amount of cross conduction will cause a decrease in the power conversion efficiency. The NCP3488 prevents cross conduction by monitoring the status of the external MOSFETs and applying the appropriate amount of "dead-time" or the time between the turn off of one MOSFET and the turn on of the other MOSFET. When the PWM input pin goes high, DRVL will go low after a propagation delay (tpdlDRVL). The time it takes for the low-side MOSFET to turn off (tfDRVL) is dependent on the total charge on the low-side MOSFET gate. The NCP3488 monitors the gate voltage of both MOSFETs and the switchnode voltage to determine the conduction status of the MOSFETs. Once the low-side MOSFET is turned off an internal timer will delay (tpdhDRVH) the turn on of the high-side MOSFET Likewise, when the PWM input pin goes low, DRVH will go low after the propagation delay (tpdDRVH). The time to turn off the high-side MOSFET (tfDRVH) is dependent on the total gate charge of the high-side MOSFET. A timer will be triggered once the high-side MOSFET has stopped conducting, to delay (tpdhDRVL) the turn on of the low-side MOSFET
Power Supply Decoupling
The PWM input and the Output Disable pins of the NCP3488 have internal protection for Electro Static Discharge (ESD), but in normal operation they present a relatively high input impedance. If the PWM controller does not have internal pull-down resistors, they should be added externally to ensure that the driver outputs do not go high before the controller has reached its under voltage lockout threshold. The NCP5388 controller does include a passive internal pull-down resistor on the drive-on output pin.
Bootstrap Circuit
The bootstrap circuit uses a charge storage capacitor (CBST) and the internal (or an external) diode. Selection of these components can be done after the high-side MOSFET has been chosen. The bootstrap capacitor must have a voltage rating that is able to withstand twice the maximum supply voltage. A minimum 50 V rating is recommended. The capacitance is determined using the following equation:
Q CBST + GATE DVBST
The NCP3488 can source and sink relatively large currents to the gate pins of the external MOSFETs. In order to maintain a constant and stable supply voltage (VCC) a low ESR capacitor should be placed near the power and ground pins. A 1 mF to 4.7 mF multi layer ceramic capacitor (MLCC) is usually sufficient.
where QGATE is the total gate charge of the high-side MOSFET, and DVBST is the voltage droop allowed on the high-side MOSFET drive. For example, a NTD60N03 has a total gate charge of about 30 nC. For an allowed droop of 300 mV, the required bootstrap capacitance is 100 nF. A good quality ceramic capacitor should be used. The bootstrap diode must be rated to withstand the maximum supply voltage plus any peak ringing voltages that may be present on SW. The average forward current can be estimated by:
IF(AVG) + QGATE fMAX
where fMAX is the maximum switching frequency of the controller. The peak surge current rating should be checked in-circuit, since this is dependent on the source impedance of the 12 V supply and the ESR of CBST.
12 V
12 V
NCP3488
4
Output Enable PWM in
BST DRVH 3 SW OD DRVL 2 IN PGND Vcc
1 8 7 5 6
Vout
Figure 4. NCP3488 Example Circuit
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NCP3488
PACKAGE DIMENSIONS
SOIC-8 D SUFFIX CASE 751-07 ISSUE AH
-X- A
8 5 NOTES: 1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982. 2. CONTROLLING DIMENSION: MILLIMETER. 3. DIMENSION A AND B DO NOT INCLUDE MOLD PROTRUSION. 4. MAXIMUM MOLD PROTRUSION 0.15 (0.006) PER SIDE. 5. DIMENSION D DOES NOT INCLUDE DAMBAR PROTRUSION. ALLOWABLE DAMBAR PROTRUSION SHALL BE 0.127 (0.005) TOTAL IN EXCESS OF THE D DIMENSION AT MAXIMUM MATERIAL CONDITION. 6. 751-01 THRU 751-06 ARE OBSOLETE. NEW STANDARD IS 751-07. MILLIMETERS MIN MAX 4.80 5.00 3.80 4.00 1.35 1.75 0.33 0.51 1.27 BSC 0.10 0.25 0.19 0.25 0.40 1.27 0_ 8_ 0.25 0.50 5.80 6.20 INCHES MIN MAX 0.189 0.197 0.150 0.157 0.053 0.069 0.013 0.020 0.050 BSC 0.004 0.010 0.007 0.010 0.016 0.050 0_ 8_ 0.010 0.020 0.228 0.244
B
1
S
4
0.25 (0.010)
M
Y
M
-Y- G
K
C -Z- H D 0.25 (0.010)
M SEATING PLANE
N
X 45 _
0.10 (0.004)
M
J
ZY
S
X
S
DIM A B C D G H J K M N S
SOLDERING FOOTPRINT*
1.52 0.060
7.0 0.275
4.0 0.155
0.6 0.024
1.270 0.050
SCALE 6:1 mm inches
*For additional information on our Pb-Free strategy and soldering details, please download the ON Semiconductor Soldering and Mounting Techniques Reference Manual, SOLDERRM/D.
ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. "Typical" parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including "Typicals" must be validated for each customer application by customer's technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
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NCP3488/D

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