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Freescale Semiconductor Advance Information
Document Number: MC34717 Rev 4.0, 12/2008
5.0 A 1.0 MHz Fully Integrated Dual Switch-Mode Power Supply
The 34717 is a highly integrated, space-efficient, low cost, dual synchronous buck switching regulator with integrated N-channel power MOSFETs. It is a high performance dual point-of-load (PoL) power supply with many desired features for the 3.3 and 5.0 V environments. Both channels can provide up to 5.0 A of continuous output current capability with high efficiency and tight output regulation. The second channel has the ability to track an external reference voltage in different configurations. The 34717 offers the designer the flexibility of many control, supervisory, and protection functions to allow for easy implementation of complex designs. It is housed in a Pb-free, thermally enhanced, and space efficient 26 Pin Exposed Pad QFN. Features * 50 m integrated N-channel power MOSFETs * Input voltage operating range from 3.0 to 6.0 V * 1% accurate output voltages, ranging from 0.7 to 3.6 V * The second output has voltage tracking capability in different configurations * Programmable switching frequency range from 200 kHz to 1.0 MHz * Programmable soft start timing * Over-current limit and short-circuit protection * Thermal shutdown * Output over-voltage and under-voltage detection * Active low power good output signal * Active low shutdown input * Pb-free packaging designated by suffix code EP.
3.0 TO 6.0 V VIN
34717
DUAL SWITCH-MODE POWER SUPPLY
EP SUFFIX (PB_FREE) 98ASA10728D 26-PIN QFN
ORDERING INFORMATION
Device MC34717EP/R2 Temperature Range (TA) -40 to 85C Package 26 QFN
34717
VIN PVIN1 BOOT1 PVIN2 BOOT2 SW2 VOUT2 INV2 VIN VOUT1 VOUT2
VOUT1
SW1 VOUT1 INV1
MCU
COMP1 COMP2 PGND1 PGND2 VDDI PG FREQ SD ILIM1 ILIM2 GND VREFIN
VMASTER
Optional
Figure 1. 34717 Simplified Application Diagram
* This document contains certain information on a new product. Specifications and information herein are subject to change without notice.
(c) Freescale Semiconductor, Inc., 2007-8. All rights reserved.
INTERNAL BLOCK DIAGRAM
INTERNAL BLOCK DIAGRAM
SD PG M1
System Reset System Control Buck Control Logic ILIM2 Current Monitoring ILIM1
Thermal Monitoring VBG Bandgap Regulator VDDI
FREQ
Oscillator
FSW ISENSE2 ISENSE1 ILIM1 BOOT1 PVIN1 M4 SW1 M5 PGND1 COMP1 ISENSE
Discharge Internal Voltage Regulator
VIN ILIM2 M3 VIN M6 BOOT2 PVIN2
M2 VIN
Gate Driver
FSW
FSW
Gate I Driver SENSE M7
SW2
INV1 VOUT1 M8
VBG Discharge
Reference Selection VBG M9 Discharge
GND
CHANNEL 1
CHANNEL 2
Figure 2. 34717 Simplified Internal Block Diagram
34717
2
-
-
+
Error Amplifier
-
Error Amplifier
PWM Comparator Ramp Generator
PWM Comparator Ramp Generator
+
PGND2 COMP2
-
+
+
INV2 VOUT2
VREFIN
Analog Integrated Circuit Device Data Freescale Semiconductor
PIN CONNECTIONS
PIN CONNECTIONS
FREQ
ILIM2
26 25 24 23 22 21 20 19 BOOT1 PVIN1 2 PVIN1 SW1 3 SW1 PGND1 4 PGND1 VOUT1 5 6 INV1 7 COMP1 8 VREFIN 9 NC 10 PG 11 12 13 COMP2 INV2 SD 15 PGND2 14 VOUT2 Transparent Top View PIN 27 16 SW2 PGND2 17 PVIN2 SW2 1 18 BOOT2 PVIN2
Figure 3. 34717 Pin Connections Table 1. 34717 Pin Definitions A functional description of each pin can be found in the Functional Pin Description section beginning on page 12.
Pin Number 1 2 3 4 5 6 7 8 9, 26 10 11 12 13 Pin Name BOOT1 PVIN1 SW1 PGND1 VOUT1 INV1
COMP1
Pin Function Passive Supply Output Ground Output Input Input Input None Output Input Input Input
Formal Name Bootstrap Power Input Voltage Switching Node Power Ground Output Voltage Discharge Path Error Amplifier Inverting Input Buck Convertor Compensation Input Reference Voltage Input No Connect Power Good Output Signal Shutdown Input Buck Convertor Compensation Input Error Amplifier Inverting Input
ILIM1
VDDI
GND
VIN
VIN
NC
Definition Channel 1 Bootstrap capacitor input pin Channel 1 Buck converter power input Channel 1 Buck converter switching node Channel 1 Buck converter and discharge MOSFETs power ground Channel 1 Buck converter output voltage discharge pin Channel 1 Buck converter error amplifier inverting input Channel 1 Buck converter external compensation network input Voltage tracking reference voltage input No internal connections to this pin. Recommend attaching a 0.1 F capacitor from pin 9 to GND. It is an active low open drain power good status reporting output Shutdown mode input control pin Channel 2 Buck converter external compensation network input Channel 2 Buck converter error amplifier inverting input
VREFIN NC PG
SD
COMP2
INV2
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PIN CONNECTIONS
Table 1. 34717 Pin Definitions (continued) A functional description of each pin can be found in the Functional Pin Description section beginning on page 12.
Pin Number 14 15 16 17 18 19 20 21 22,23 24 25 27 Pin Name VOUT2 PGND2 SW2 PVIN2 BOOT2 ILIM1 ILIM2 FREQ
VIN
Pin Function Output Ground Output Power Input Input Input Input Power Ground Output Ground
Formal Name Output Voltage Discharge Path Power Ground Switching Node Power Input Voltage Bootstrap Input Soft Start Adjustment Input CH 1 Soft Start Adjustment Input CH 2 Frequency Adjustment Input Input Supply Voltage Signal Ground Internal Supply Voltage Thermal Pad
Definition Channel 2 Buck converter output voltage discharge pin Channel 2 Buck converter and discharge MOSFETs power ground Channel 2 Buck converter switching node Channel 2 Buck converter power input Channel 2 Bootstrap capacitor input pin Channel 1 soft start adjustment Channel 2 soft start adjustment The buck converters switching frequency adjustment input Power supply voltage of the IC Analog ground of the IC Internal Supply Voltage Output Thermal pad for heat transfer. Connect the thermal pad to the analog ground and the ground plane for heat sinking.
GND VDDI GND
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Analog Integrated Circuit Device Data Freescale Semiconductor
ELECTRICAL CHARACTERISTICS MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
MAXIMUM RATINGS
Table 2. Maximum Ratings All voltages are with respect to ground unless otherwise noted. Exceeding these ratings may cause a malfunction or permanent damage to the device.
Ratings ELECTRICAL RATINGS Input Supply Voltage (VIN) Pin High Side MOSFET Drain Voltage (PVIN1, PVIN2) Pins Switching Node (SW1, SW2) Pins BOOT1, BOOT2 Pins (Referenced to SW1, SW2 Pins Respectively) PG, VOUT1, VOUT2, and SD Pins VDDI, FREQ, ILIM1, ILIM2, INV1, INV2, COMP1, COMP2, and VREFIN Pins Channel 1 Continuous Output Current(1) Channel 2 Continuous Output Current(1) ESD Voltage(2) Human Body Model Machine Model (MM) Charge Device Model THERMAL RATINGS Operating Ambient Temperature(3) Storage Temperature Peak Package Reflow Temperature During Reflow(4),(5) Maximum Junction Temperature Power Dissipation (TA = 85C)(6) Notes 1. Continuous output current capability so long as TJ is TJ(MAX). 2. 3. 4. 5. ESD testing is performed in accordance with the Human Body Model (HBM) (CZAP = 100 pF, RZAP = 1500 ), the Machine Model (MM) (CZAP = 200 pF, RZAP = 0 ), and the Charge Device Model (CDM), Robotic (CZAP = 4.0 pF). The limiting factor is junction temperature, taking into account power dissipation, thermal resistance, and heatsinking. Pin soldering temperature limit is for 10 seconds maximum duration. Not designed for immersion soldering. Exceeding these limits may cause malfunction or permanent damage to the device. Freescale's Package Reflow capability meets Pb-free requirements for JEDEC standard J-STD-020C. For Peak Package Reflow Temperature and Moisture Sensitivity Levels (MSL), Go to www.freescale.com, search by part number [e.g. remove prefixes/suffixes and enter the core ID to view all orderable parts. (i.e. MC33xxxD enter 33xxx), and review parametrics. Maximum power dissipation at indicated ambient temperature. TA TSTG TPPRT TJ(MAX) PD -40 to 85 -65 to +150 Note 5 +150 2.03 C C C C W VESD1 VESD2 VESD3 2000 200 750 VIN PVIN VSW VBOOT - VSW IOUT1 IOUT2 -0.3 to 7.0 -0.3 to 7.0 -0.3 to 7.0 -0.3 to 7.0 -0.3 to 7.0 -0.3 to 3.0 +5.0 +5.0 V V V V V V A A V Symbol Value Unit
6.
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ELECTRICAL CHARACTERISTICS MAXIMUM RATINGS
Table 2. Maximum Ratings (continued) All voltages are with respect to ground unless otherwise noted. Exceeding these ratings may cause a malfunction or permanent damage to the device.
Ratings THERMAL RESISTANCE(7) Thermal Resistance, Junction to Ambient, Single-Layer Board (1s)(8) Thermal Resistance, Junction to Ambient, Four-Layer Board (2s2p) Thermal Resistance, Junction to Board
(10) (9)
Symbol
Value
Unit
RJA RqJMA RqJB
93 32 13.6
C/W C/W C/W
Notes 7. The PVIN, SW, and PGND pins comprise the main heat conduction paths. 8. Per SEMI G38-87 and JEDEC JESD51-2 with the single-layer board (JESD51-3) horizontal. 9. Per JEDEC JESD51-6 with the board (JESD51-7) horizontal. There are thermal vias connecting the package to the two planes in the board. (per JESD51-5) 10. Thermal resistance between the device and the printed circuit board per JEDEC JESD51-8. Board temperature is measured on the top surface of the board near the package.
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ELECTRICAL CHARACTERISTICS STATIC ELECTRICAL CHARACTERISTICS
STATIC ELECTRICAL CHARACTERISTICS
Table 3. Static Electrical Characteristics Characteristics noted under conditions 3.0 V VIN 6.0 V, - 40C TA 85C, GND = 0 V, unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25C under nominal conditions, unless otherwise noted.
Characteristic IC INPUT SUPPLY VOLTAGE (VIN) Input Supply Voltage Operating Range Input DC Supply Current(11) (Normal Mode: SD = 1, Unloaded Outputs) Input DC Supply Current(11) (Shutdown Mode, SD = 0) INTERNAL SUPPLY VOLTAGE OUTPUT (VDDI) Internal Supply Voltage Range VDDI 2.35 2.5 2.65 V IINOFF 100 A IIN 35 mA VIN 3.0 6.0 V Symbol Min Typ Max Unit
CHANNEL 1 BUCK CONVERTER (PVIN1, SW1, PGND1, BOOT1, INV1, COMP1, ILIM1) Channel 1 High Side MOSFET Drain Voltage Range Output Voltage Adjustment Range(12) Output Voltage Accuracy(12),(13) Line Regulation(12) (Normal Operation, VIN = 3.0 to 6.0 V, IOUT1 = 2.5 A) Load Regulation(12) (Normal Operation, IOUT1 = 0.0 to 5.0 A) Error Amplifier Reference Voltage(12) Output Under-voltage Threshold Output Over-voltage Threshold Continuous Output Current Over-current Limit Soft Start Adjusting Reference Voltage Range Short-circuit Current Limit High Side N-CH Power MOSFET (M4) (IOUT1 = 1.0 A, VBOOT1 - VSW1= 3.3 V) Low Side N-CH Power MOSFET (M5) RDS(ON)(12) (IOUT1 = 1.0 A, VIN = 3.3 V) M2 RDS(ON) (VIN = 3.3 V, M2 is on) RDS(ON)LS1 RDS(ON)M2 10 50 m RDS(ON)(12) REGLD1 VREF1 VUVR1 VOVR1 IOUT1 ILIM1 VILIM1 ISHORT1 RDS(ON)HS1 -1.0 -8.0 1.5 1.25 10 0.7 6.5 8.5 1.0 -1.5 8.0 5.0 VDDI 50 % V % % A A V A m REGLN1 -1.0 1.0 % PVIN VOUTHI1 2.5 0.7 -1.0 6.0 3.6 1.0 V V %
2.0
-
4.0
Notes 11. Section "MODES OF OPERATION", page 16 has a detailed description of the different operating modes of the 34717 12. Design information only, this parameter is not production tested. 13. This is directly affected by the accuracy of the external feedback network, 1% feedback resistors are recommended.
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ELECTRICAL CHARACTERISTICS STATIC ELECTRICAL CHARACTERISTICS
Table 3. Static Electrical Characteristics Characteristics noted under conditions 3.0 V VIN 6.0 V, - 40C TA 85C, GND = 0 V, unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25C under nominal conditions, unless otherwise noted.
Characteristic SW1 Leakage Current (Standby and Shutdown modes) PVIN1 Pin Leakage Current (Shutdown Mode) Error Amplifier DC Gain(14) Error Amplifier Unit Gain Bandwidth Error Amplifier Slew Error Amplifier Input Rate(14) Offset(14)
(14)
Symbol ISW IPVIN1 AEA UGBWEA SREA OFFSETEA IINV1 TSDFET1 TSDHYFET1
Min -10 -10 -3.0 -1.0 -
Typ 150 3.0 7.0 0 170 25
Max 10 10 3.0 1.0 -
Unit A A dB MHz V/s mV A C C
INV1 Pin Leakage Current Thermal Shutdown Thermal Shutdown Threshold(14) Hysteresis(14)
CHANNEL 2 BUCK CONVERTER (PVIN2, SW2, PGND2, BOOT2, INV2, COMP2, ILIM2) Channel 2 High Side MOSFET Drain Voltage Range Output Voltage Adjustment Range Output Voltage Accuracy Line Regulation(14) REGLN2 REGLD2 VREF2 VUVR2 VOVR2 IOUT2 ILIM2 VILIM2 ISHORT2 RDS(ON)(14) RDS(ON)HS2 RDS(ON)LS2 -1.0 1.0 %
(14)
PVIN VOUTHI2 -
2.5 0.7 -1.0
-
6.0 3.6 1.0
V V %
(14),(15),(16)
(Normal Operation, VIN = 3.0 to 6.0 V, IOUT2 = 2.5 A) Load Regulation(14) (Normal Operation, IOUT2 = 0.0 to 5.0 A) Error Amplifier Reference Voltage(14) Output Under-voltage Threshold Output Over-voltage Threshold Continuous Output Current Over-current Limit Soft Start Adjusting Reference Voltage Range Short-circuit Current Limit High Side N-CH Power MOSFET (M6) (IOUT2 = 1.0 A, VBOOT2 - VSW2= 3.3 V) Low Side N-CH Power MOSFET (M7) RDS(ON)(14) (IOUT2 = 1.0 A, VIN = 3.3 V) M3 RDS(ON) (VIN = 3.3 V, M3 is on) SW2 Leakage Current (Standby and Shutdown modes) PVIN2 Pin Leakage Current (Shutdown Mode)
-1.0 -8.0 1.5 1.25 10
0.7 6.5 8.5 -
1.0 -1.5 8.0 5.0 VDDI 50
% V % % A A V A m
10
-
50
m
RDS(ON)M3 ISW IPVIN2
2.0 -10 -10
-
4.0 10 10
A A
Notes 14. Design information only, this parameter is not production tested. 15. This is directly affected by the accuracy of the external feedback network, 1% feedback resistors are recommended. 16. 1% is assured at room temperature
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Analog Integrated Circuit Device Data Freescale Semiconductor
ELECTRICAL CHARACTERISTICS STATIC ELECTRICAL CHARACTERISTICS
Table 3. Static Electrical Characteristics Characteristics noted under conditions 3.0 V VIN 6.0 V, - 40C TA 85C, GND = 0 V, unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25C under nominal conditions, unless otherwise noted.
Characteristic Error Amplifier DC Gain(17) Error Amplifier Unit Gain Bandwidth Error Amplifier Slew Rate(17)
(17) (17)
Symbol AEA UGBWEA SREA OFFSETEA IINV2 TSDFET2 TSDHYFET2
Min -3.0 -1.0 -
Typ 150 3.0 7.0 0 170 25
Max 3.0 1.0 -
Unit dB MHz V/s mV A C C
Error Amplifier Input Offset INV2 Pin Leakage Current Thermal Shutdown
Threshold(17)
(17)
Thermal Shutdown Hysteresis OSCILLATOR (FREQ)
Oscillator Frequency Adjusting Reference Voltage Range TRACKING (VREFIN, VOUT1, VOUT2) VREFIN External Reference Voltage Range(17) VOUT1 Total Discharge VOUT2 Total Discharge Resistance(17) Resistance(17)
VFREQ
0.0
-
VDDI
V
VREFIN RTDS(M8) RTDS(M9)
0.0 -
50 50
1.35 -
V
CONTROL AND SUPERVISORY (SD, PG) SD High Level Input Voltage SD Low Level Input Voltage SD Pin Internal Pull-up Resistor PG Low Level Output Voltage (IPG = 3.0 mA) PG Pin Leakage Current (M1 is off, Pulled up to VIN) Notes 17. Design information only, this parameter is not production tested. IPGLKG -1.0 1.0 A VPGLO 0.4 V VSDHI VSDLO RSDUP 2.0 1.0 0.4 2.0 V V M
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ELECTRICAL CHARACTERISTICS DYNAMIC ELECTRICAL CHARACTERISTICS
DYNAMIC ELECTRICAL CHARACTERISTICS
Table 4. Dynamic Electrical Characteristics Characteristics noted under conditions 3.0 V VIN 6.0 V, - 40C TA 85C, GND = 0 V, unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25C under nominal conditions, unless otherwise noted.
Characteristic Symbol Min Typ Max Unit
CHANNEL 1 BUCK CONVERTER (PVIN1, SW1, PGND1, BOOT1, INV1, COMP1, ILIM1) Switching Node (SW1) Rise Time(18) (PVIN = 3.3 V, IOUT1 = 5.0 A) Switching Node (SW1) Fall Time(18) (PVIN = 3.3 V, IOUT1 = 5.0 A) Minimum OFF Time Minimum ON Time Soft Start Duration (Normal Mode) ILIM1: 1.25 to 1.49 V 1.5 to 1.81 V 1.82 to 2.13 V 2.14 to 2.5 V Over-current Limit Timer Over-current Limit Retry Timeout Period Output Under-voltage/Over-voltage Filter Delay Timer tLIM1 tTIMEOUT1 tFILTER1 tFALL1 tOFFMIN tONMIN tSS1 80 5.0 3.2 1.6 0.8 0.4 10 120 25 ms ms s ms tRISE1 8.0 ns
-
5.0
-
ns ns ns
-
150 0(19)
-
CHANNEL 2 BUCK CONVERTER (PVIN2, SW2, PGND2, BOOT2, INV2, COMP2, ILIM2) Switching Node (SW2) Rise Time(18) (PVIN = 3.3 V, IOUT2 = 5.0 A) Switching Node (SW2) Fall Time(18) (PVIN = 3.3 V, IOUT2 = 5.0 A) Minimum OFF Time Minimum ON Time Soft Start Duration (Normal Mode) ILIM2: 1.25 to 1.49 V 1.5 to 1.81 V 1.82 to 2.13 V 2.14 to 2.5 V Over-current Limit Timer Over-current Limit Retry Timeout Period Output Under-voltage/Over-voltage Filter Delay Timer OSCILLATOR (FREQ)(20) tLIM2 tTIMEOUT2 tFILTER2 tFALL2 tOFFMIN tONMIN tSS2 80 5.0 3.2 1.6 0.8 0.4 10 120 25 ms ms s tRISE2 28 ns
-
12.0
-
ns ns ns ms
-
150 0
(19)
-
Notes 18. Design information only, this parameter is not production tested. 19. The regulator has the ability to enter into pulse skip mode when the inductor current ripple reaches the threshold for the LS zero detect, which has a typical value of 500 mA. 20. Oscillator frequency is 10%
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ELECTRICAL CHARACTERISTICS DYNAMIC ELECTRICAL CHARACTERISTICS
Table 4. Dynamic Electrical Characteristics Characteristics noted under conditions 3.0 V VIN 6.0 V, - 40C TA 85C, GND = 0 V, unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25C under nominal conditions, unless otherwise noted.
Characteristic Oscillator Default Switching Frequency (FREQ = GND) Oscillator Switching Frequency Range CONTROL AND SUPERVISORY (SD, PG) PG Reset Delay Thermal Shutdown Retry Timeout Period(21) tPGRESET tTIMEOUT 8.0 80 12 120 ms ms FSW FSW 200 1.0 1000 MHz kHz Symbol Min Typ Max Unit
Notes 21. Design information only, this parameter is not production tested.
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FUNCTIONAL DESCRIPTION INTRODUCTION
FUNCTIONAL DESCRIPTION
INTRODUCTION
Today's advanced systems are increasingly requiring more efficient and accurate power supplies. They present a set of challenges that include highly accurate voltage regulation, high current and fast transient response capability, voltage monitoring (power sequencing), and increased operating frequency. Point of Load power supplies offer adequate solutions to these challenges. They are nonisolated DC to DC converters that are located near their load and take their input voltage from an intermediate not, necessarily, regulated bus. their close proximity to the load is of a high importance with newer device requirements. While meeting the challenges, they allow for higher efficiency, localized protection, and minimum distribution losses. Their compact design and value makes them cost effective. The 34717 is a PoL dual output power supply. Its integrated solution offers a cost effective system and reliable operation. It utilizes a voltage mode synchronous buck switching converter topology with integrated low RDS(ON) (50 m) N-channel power MOSFETs for higher efficiency operation. It provides an output voltage with an accuracy of less than 2.0%, and capable of supplying up to 5.0 A of continuous current from both channels. The second output tracking abilities makes it ideal for systems with multiple related supply rails. It has a programmable switching frequency that allows for flexibility and optimization over the operating conditions and can operate at up to 1.0 MHz to significantly reduce the external components size and cost. It also provides the ability to program the over current limit for both channels. It protects against output over-current, overvoltage, under-voltage, and over-temperature conditions. It also protects the system from short circuit events. It incorporates a power good output signal to alert the host when a fault occurs. It can be enabled and disabled by controlling the SD pin, which offers power sequencing capabilities. By integrating the control/supervisory circuitry along with the Power MOSFET switches for the buck converter into a space-efficient package, the 34717 offers a complete, smallsize, cost-effective, and simple solution to satisfy the needs of today's systems.
FUNCTIONAL PIN DESCRIPTION BOOTSTRAP INPUT (BOOT1, BOOT2)
Bootstrap capacitor input pin. Connect a capacitor (as discussed in Bootstrap capacitor on page 21) between this pin and the SW pin of the respective channel to enhance the gate of the high side Power MOSFET during switching. divider and connect the VTT voltage (channel 2) directly to INV2 pin.
INTERNAL SUPPLY VOLTAGE OUTPUT (VDDI)
This is the output of the internal bias voltage regulator. Connect a 1.0 F, 6.0 V low ESR ceramic filter capacitor between this pin and the GND pin. Filtering any spikes on this output is essential to the internal circuitry stable operation.
POWER INPUT VOLTAGE (PVIN1, PVIN2)
Buck converter power input voltage. This is the drain of the buck converter high side power MOSFET.
SIGNAL GROUND (GND) SWITCHING NODE (SW1, SW2)
Buck converter switching node. This pin is connected to the output inductor. Analog ground of the IC. Internal analog signals are referenced to this pin voltage.
INPUT SUPPLY VOLTAGE (VIN) POWER GROUND (PGND1, PGND2)
Buck converter and discharge MOSFETs power ground. It is the source of the buck converter low side power MOSFET. IC power supply input voltage. Input filtering is required for the device to operate properly.
POWER GOOD OUTPUT SIGNAL (PG) COMPENSATION INPUT (COMP1, COMP2)
Buck converter external compensation network connects to this pin. Use a type III compensation network. This is an active low open drain output that is used to report the status of the device to a host. This output activates after a successful power up sequence and stays active as long as the device is in normal operation and is not experiencing any faults. This output activates after a 10 ms delay and must be pulled up by an external resistor to a supply voltage like VIN.
ERROR AMPLIFIER INVERTING INPUT (INV1, INV2)
Buck converter error amplifier inverting input. Connect the VDDQ voltage (channel 1) to INV1 pin through a resistor
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Analog Integrated Circuit Device Data Freescale Semiconductor
FUNCTIONAL DESCRIPTION FUNCTIONAL PIN DESCRIPTION
SHUTDOWN INPUT (SD)
If this pin is tied to the GND pin, the device will be in Shutdown mode. If left unconnected or tied to the VIN pin, the device will be in Normal mode. The pin has an internal pullup of 1.5 M.
FREQUENCY ADJUSTMENT INPUT (FREQ)
The buck converters switching frequency can be adjusted by connecting this pin to an external resistor divider between VDDI and GND pins. The default switching frequency (FREQ pin connected to ground, GND) is set at 1.0 MHz.
REFERENCE VOLTAGE INPUT (VREFIN)
The output of channel two will track the voltage applied at this pin.
SOFT START ADJUSTMENT INPUT (ILIM1, ILIM2)
Soft Start can be adjusted by applying a voltage between 1.25 V and VDDI on each ILIM pin.
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FUNCTIONAL DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
MC34717 - Functional Block Diagram
Internal Bias Circuits
System Control and Logic
Oscillator
Protection Functions
Control and Supervisory Functions
Tracking and Sequencing
2 x Buck Converter
Figure 4. Block Illustration
INTERNAL BIAS CIRCUITS
This block contains all circuits that provide the necessary supply voltages and bias currents for the internal circuitry. It consists of: * Internal voltage supply regulator: This regulator supplies the VDDI voltage that is used to drive the digital/ analog internal circuits. It is equipped with a Power-OnReset (POR) circuit that watches for the right regulation levels. External filtering is needed on the VDDI pin. This block will turn off during the shutdown mode. * Internal bandgap reference voltage: This supplies the reference voltage to some of the internal circuitry. * Bias circuit: This block generates the bias currents necessary to run all of the blocks in the IC.
programmed by connecting a resistor divider to the FREQ pin, between VDDI and GND pins (See Figure 1).
PROTECTION FUNCTIONS
This block contains the following circuits: * Over-current limit and short-circuit detection: This block monitors the output of the buck converters for overcurrent conditions and short-circuit events and alerts the system control for further command. * Thermal limit detection: This block monitors the temperature of the device for overheating events. If the temperature rises above the thermal shutdown threshold, this block will alert the system control for further commands. * Output over-voltage and under-voltage monitoring: This block monitors the buck converters output voltages to ensure they are within regulation boundaries. If not, this block alerts the system control for further commands.
SYSTEM CONTROL AND LOGIC
This block is the brain of the IC where the device processes data and reacts to it. Based on the status of the SD pin, the system control reacts accordingly and orders the device into the right status. It also takes inputs from all of the monitoring/protection circuits and initiates power up or power down commands. It communicates with the buck converter to manage the switching operation and protects it against any faults.
CONTROL AND SUPERVISORY FUNCTIONS
This block is used to interface with an outside host. It contains the following circuits. * Shutdown control input: An outside host can put the 34717 device into shutdown mode by sending a logic "0" to the SD pin. * Power good output signal: The 34717 can communicate to an outside host that a fault has occurred by pulling the voltage on the PG pin high.
OSCILLATOR
This block generates the clock cycles necessary to run the IC digital blocks. It also generates the buck converters switching frequency. The switching frequency can be
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FUNCTIONAL DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION
TRACKING AND SEQUENCING
This block allows the second output of the 34717 to track the voltage applied at the VREFIN pin in different tracking configurations. This will be discussed in further details later in this document. For power down during a shutdown mode, the 34717 uses internal discharge MOSFETs (M8 and M9 on Figure 2, page 2) to discharge the first and second output respectively. The discharge MOSFETs are only active during shutdown mode. Using this block along with controlling the SD pin can offer the user power sequencing capabilities by controlling when to turn the 34717 outputs on or off.
BUCK CONVERTER
This block provides the main function of the 34717: DC to DC conversion from an un-regulated input voltage to a regulated output voltage used by the loads for reliable operation. The buck converter is a high performance, fixed
frequency (externally adjustable), synchronous buck PWM voltage-mode control. It drives integrated 50m N-channel power MOSFETs saving board space and enhancing efficiency. The switching regulator output voltage is adjustable with an accuracy of less than 2% to meet today's requirements. The second channel's output has the ability to track the voltage applied at the VREFIN pin. The regulator's voltage control loop is compensated using a type III compensation network, with external components to allow for optimizing the loop compensation, for a wide range of operating conditions. A typical Bootstrap circuit with an internal PMOS switch is used to provide the voltage necessary to properly enhance the high side MOSFET gate. The 34717 has the ability to supply up to 5.0 A of continuous current from each channel, making it suitable for many high current applications.
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FUNCTIONAL DEVICE OPERATION OPERATIONAL MODES
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
SD = 0 VOUT2<=VUVF2 VOUT2 Under-voltage VOUT1=ON VOUT2=ON PG = 1 VOUT2>=VOVR2 VOUT2 Over-voltage VOUT1=ON VOUT2=ON PG = 1 VOUT2=>=VUVR2 Shutdown FSW is programmed VOUT1 = Discharge VOUT2 = Discharge PG = 1 SD =1 Power Off VOUT1=OFF VOUT2=OFF PG = 1 3.0 V<=VIN<=6.0 V
VIN < 3.0 V VOUT1<=VOUT1 VOUT1 Under-voltage VOUT1=ON VOUT2=ON PG = 1 VOUT1 >= VUVR1 VOUT1>=VOVR1
VOUT2<=VOVF2
TJ >= 170C
TJ<=145C
TIMEOUT Expired Channel 2 Thermal Shutdown VOUT1=ON VOUT2=OFF PG = 1 TIMEOUT Expired Channel 2 Over-current VOUT1=ON VOUT2=OFF PG = 1 TIMEOUT=1 IOUT2>=ILIM2
For>=10 ms
Normal FSW is programmed ILM1, ILM2 are programmed VOUT1 and VOUT2 tss = 1 VOUT1 = ON VOUT2 = ON PG = 0
VOUT1 <= VOVF1
VOUT1 Over-voltage VOUT1=ON VOUT2=ON PG = 1 TJ>=170C
TJ<=145C TIMEOUT Expired
TIMEOUT Expired VOUT2 Short-circuit VOUT1=ON VOUT2=OFF PG = 1 TIMEOUT=1
TIMEOUT Expired VOUT1 Short-circuit VOUT1=OFF VOUT2=ON PG = 1 TIMEOUT=1
TIMEOUT Expired
Channel 1 Thermal Shutdown VOUT1=OFF VOUT2=ON PG = 1
Channel 1 Over-current VOUT1=OFF VOUT2=ON PG = 1 TIMEOUT=1
IOUT1>=ILIM1 For>=10 ms
IOUT2>=ISHORT2
IOUT1>=ISHORT1
Figure 5. Operation Modes Diagram
MODES OF OPERATION
The 34717 has two primary modes of operation: Normal Mode In Normal mode, all functions and outputs are fully operational. To be in this mode, the VIN needs to be within its operating range, Shutdown input is high, and no faults are present. This mode consumes the most amount of power. Shutdown Mode In this mode, activated by pulling the SD pin low, the chip is in a shutdown state and the output is disabled and discharged. In this mode, the 34717 consumes the least amount of power since almost all of the internal blocks are disabled.
START-UP SEQUENCE
When power is first applied, the 34717 checks the status of the SD pin. If the device is in a shutdown mode, no block will power up and the output will not attempt to ramp. Once
the SD pin is set to high, the VDDI internal supply voltage and the bias currents will be established, so the internal VDDI POR signal can be released. The rest of the internal blocks will be enabled and the buck converter switching frequency and soft start timing values are determined by reading the FREQ, ILIM1, and ILIM2 pins. A soft start cycle is then initiated to ramp up the output of the buck converter. The first channel uses an internal 0.7 V reference for its error amplifier while the second channel's error amplifier uses the voltage on the VREFIN pin as its reference voltage until VREFIN is equal to 0.7 V, then the error amplifier defaults to the internal 0.7 V reference voltage. This method allows the second output to achieve multiple tracking configurations as will be explained later in this document. Soft start is used to prevent the output voltage from overshooting during startup. At initial startup, the output capacitor is at zero volts; VOUT = 0 V. Therefore, the voltage across the inductor will be PVIN during the capacitor charge phase which will create a very sharp di/dt ramp. Allowing the inductor current to rise too high can result in a large difference between the charging current and the actual load
34717
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Analog Integrated Circuit Device Data Freescale Semiconductor
FUNCTIONAL DEVICE OPERATION OPERATIONAL MODES
current that can result in an undesired voltage spike once the capacitor is fully charged. The soft start is active each time the IC goes out of standby or shutdown mode, power is recycled, or after a fault retry. After a successful start-up cycle where the device is enabled, no faults have occurred, and the output voltage has reached its regulation point, the 34717 pulls the power good output signal low after a 10 ms reset delay, to indicate to the host that the device is in normal operation.
detecting device by sampling a ratio of the load current. That sample is compared via the comparator with an internal reference to determine if the output is in over-current or not. If the peak current in the output inductor reaches the over current limit (ILIM), the converter will start a cycle-by-cycle operation to limit the current, and a 10 ms over-current limit timer (tLIM) starts. The converter will stay in this mode of operation until one of the following occurs: * The current is reduced back to the normal level before tLIM expires, and in this case normal operation is regained. * tLIM expires without regaining normal operation, at which point the device turns off the output and the power good output signal is pulled high. At the end of a time-out period of 100 ms (tTIMEOUT), the device will attempt another soft start cycle. * The device reaches the thermal shutdown limit (TSDFET) and turns off the output. The power good output signal is pulled high. * The output current keeps increasing until it reaches the short-circuit current limit (ISHORT). See below for more details. Short-circuit Current Limit This block uses the same current detection mechanism as the over-current limit detection block. If the load current reaches the ISHORT value, the device reacts by shutting down the output immediately. This is necessary to prevent damage in case of a permanent short circuit. Then, at the end of a timeout period of 100 ms (tTIMEOUT), the device will attempt another soft start cycle. Thermal Shutdown Thermal limit detection block monitors the temperature of the device and protects against excessive heating. If the temperature reaches the thermal shutdown threshold (TSDFET), the converter output switches off and the power good output signal indicates a fault by pulling high. The device will stay in this state until the temperature has decreased by the hysteresis value and then After a timeout period (tTIMEOUT) of 100 ms, the device will retry automatically and the output will go through a soft start cycle. If successful normal operation is regained, the power good output signal is asserted low to indicate it.
PROTECTION FUNCTIONS
The 34717 monitors the application for several fault conditions to protect the load from overstress. The reaction of the IC to these faults ranges from turning off the outputs to just alerting the host that something is wrong. In the following paragraphs, each fault condition is explained: Output Over-voltage An over-voltage condition occurs once the output voltage goes higher than the rising over-voltage threshold (VOVR). In this case, the power good output signal is pulled high, alerting the host that a fault is present, but the output will stay active. To avoid erroneous over-voltage conditions, a 20 s filter is implemented. The buck converter will use its feedback loop to attempt to correct the fault. Once the output voltage falls below the falling over-voltage threshold (VOVF), the fault is cleared and the power good output signal is pulled low, the device is back in normal operation. Output Under-voltage An under-voltage condition occurs once the output voltage falls below the falling under-voltage threshold (VUVF). In this case, the power good output signal is pulled high, alerting the host that a fault is present, but the output will stay active. To avoid erroneous under-voltage conditions, a 20 s filter is implemented. The buck converter will use its feedback loop to attempt to correct the fault. Once the output voltage rises above the rising under-voltage threshold (VUVR), the fault is cleared and the power good output signal is pulled low, the device is back in normal operation. Output Over-current This block detects over-current in the Power MOSFETs of the buck converter. It is comprised of a sense MOSFET and a comparator. The sense MOSFET acts as a current
34717
Analog Integrated Circuit Device Data Freescale Semiconductor
17
TYPICAL APPLICATIONS
TYPICAL APPLICATIONS
C14 0.1 F VDDI BOOT1 C28 SW1 0.1 F PVIN1 SW1 1 2 2 3 3 PGND1 4 4 5 C27 0.1 F VOUT1 26 25 VDDI NC
VIN FREQ ILIM2 ILIM1 24 23 22 GND VIN VIN 21 20 19 FREQ ILIM2 ILIM1 18 17 17 16 16 15 15 14 C11 0.1 F VOUT2 PGND2 BOOT2 C15 SW2 0.1 F PVIN2 SW2
BOOT1 PVIN1 PVIN1 SW1 SW1 PGND1 PGND1 VREFIN COMP1
BOOT2 PVIN2 PVIN2
MC34717
SW2 SW2 PGND2 PGND2 COMP2 VOUT2 INV2
VOUT1 INV1
PG PG
NC
6
7
8
9 10
11 12 13 INV2 SD COMP2
INV1 COMP1 VREFIN C13 0.1 F
C12 0.1 F
Compensation Network SW1
VO1 INV2 C18 15 pF R15 22 k C19 0.75 nF R14 560 R2 12.7 k
SD
Compensation Network SW2
VO2 INV2
COMP1
C20 0.910 nF
R1 20 k
COMP2
C21 20 pF R19 15 k C22 1.8 nF R18 300
C230 1.0 nF
R4 20 k
R2 17.4 k
Buck Converter 1
SW1 D3 PMEG2010EA _nopop L1 1 H Vo1_2 Vo1_1 VO1 SW2 D2 OMEG2010EA _nopop
Buck Converter 2
L1 1.5 H Vo2_2 Vo2_1 VO2 R30 4.7_nopop C7 C6 C8 C9 100 F100 F 100 F 1 nF_nopop
R20 4.7_nopop C10 C24 C26 100 F100 F C25 100 F 1 nF_nopop
34717
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Analog Integrated Circuit Device Data Freescale Semiconductor
TYPICAL APPLICATIONS
Figure 6. 34717 Typical Application
I/O Signals
J2 PVIN1 VO1 GND 3 2 1 J3
VIN Capacitors
VIN C17 10 F C16 0.1 F
PGOOD LED
VIN R7 1k D1 LED LED
VMASTER
VM
R8 10k R9 10k
VMASTER
PVIN2 VO2 GND VM VIN GND
3 2 1 3 2 1
J4
Jumpers
VO1 VMASTER STBY_nopop LED 1 2 1 SD 2 CON10A 1 3 5 7 9 J1 2 4 6 8 10 VREFIN PG x SD VDDI R16 10 k
ILIM1, ILIM2, FREQ
VDDI R10 10 k ILIM2 R13 10 k_nopop VDDI R12 10 k FREQ R11 10 k_nopop
ILIM1 R22 10 k_nopop
PVIN1 Capacitors
PVIN1 PVIN2
PVIN2 Capacitors
C1 0.1 F
C2 1.0 F
C3 C4 C5 100 F 100 F 100 F
C30 0.1 F
C31 1.0 F
C32 C33 C29 1002 F 100 F 100 F
Trimpots nopop
VDDI ILIM1 ILIM2 FREQ R21 R5 R6 POT_50 k_nopop POT_50 k_nopop POT_50 k_nopop
Figure 7. 34717 Typical Application
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Analog Integrated Circuit Device Data Freescale Semiconductor
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TYPICAL APPLICATIONS
CONFIGURING THE OUTPUT VOLTAGE:
Both channels for the 34717 are general purpose DC-DC converters. The resistor divider to the INV node is responsible for setting the output voltage. The equation is:
680 733 787 840
0.936 - 1.092 0.781 - 0.936 0.625 - 0.780 0.469 - 0.624 0.313 - 0.468 0.157 - 0.312 0.000 - 0.156
VOUT
R1 = V REF + 1 R2
893 947 1000
For channel 1: VREF=VBG=0.7V. For channel 2: The second channel of the 34717 has an internal reference selector, thus VREF can be either the voltage at VREFIN terminal or the internal reference voltage VBG. The reference value is given by the following condition: VREF=VREFIN if VREFIN is less than VBG=0.7 V. Otherwise, VREF=VBG. Usually the output regulation voltage is calculated using the internal reference VBG, and the condition VREF=VREFIN is used for tracking purposes.
Table 5. Frequency Selection Table
SOFT START ADJUSTMENT
Table 6 shows the voltage that should be applied to the ILIM1and ILIM2 pins to get the desired soft start timing.
SOFT START [MS] 3.2 1.6 0.8 0.4 VOLTAGE APPLIED TO ILIM 1.19 - 1.49 V 1.50 - 1.81 V 1.82 - 2.13 V 2.14 - 2.50 V
SWITCHING FREQUENCY CONFIGURATION
The switching frequency will have a value of 1.0MHz by connecting the FREQ terminal to the GND. If the smallest frequency value of 200 kHz is desired, then connect the FREQ terminal to VDDI. To program the switching frequency to another value, an external resistor divider must be connected to the FREQ terminal to achieve the voltages given by Table 5.
Table 6. Soft Start Configurations
FREQUENCY 200 253 307 360 413 466 520 573 627
VOLTAGE APPLIED TO PIN FREQ RFQH 2.341 - 2.500 2.185 - 2.340 2.029 - 2.184 1.873 - 2.028 1.717 - 1.872 1.561 - 1.716 1.405 - 1.560 1.249 - 1.404 1.093 - 1.248 CVDDI RIL RIH RIL RIH RFQL
VDDI FREQ ILIM1
GND
Figure 8. Resistor Divider for Frequency and Soft Start Adjustment
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Analog Integrated Circuit Device Data Freescale Semiconductor
TYPICAL APPLICATIONS
SELECTING INDUCTOR
The Inductor calculation process is the same for both Channels. The equation is the following:
dt _ I _ rise =
T * I OUT I OUT _ step
L = D'MAX T
D 'MAX
T
(VOUT + I OUT * ( Rds(on) _ ls + r _ w)) I OUT VOUT Maximum Off Time Percentage = 1- Vin _ max
Switching Period Drain - to - Source Resistance of FET Winding Resistance of Inductor Output Current Ripple
The following formula is helpful to find the maximum allowed ESR.
ESRmax =
VOUT * Fsw * L VOUT (1 - D min)
Rds(on) _ ls
r_w I OUT
The effects of the ESR is often neglected by the designers and may present a hidden danger to the ultimate supply stability. Poor quality capacitors have a widely disparate ESR value, which can make the closed loop response inconsistent.
SELECTING THE OUTPUT FILTER CAPACITOR
The following considerations are most important for the output capacitor, and not the actual Farad value: the physical size, the ESR of the capacitor, and the voltage rating. Calculate the minimum output capacitor using the following formula:
BOOTSTRAP CAPACITOR
The bootstrap capacitor is needed to supply the gate voltage for the high side MOSFET. This N-Channel MOSFET needs a voltage difference between its gate and source to be able to turn on. The high side MOSFET source is the SW node, so it is not at ground and it is floating and shifting in voltage. We cannot just apply a voltage directly to the gate of the high side that is referenced to ground. We need a voltage referenced to the SW node. This is why the bootstrap capacitor is needed. This capacitor charges during the high side off time. The low side will be on during that time. The SW node and the bottom of the bootstrap capacitor will be connected to ground, and the top of the capacitor will be connected to a voltage source. The capacitor will charge up to that voltage source (for example 5.0 V). Now when the low side MOSFET switches off and the high side MOSFET switches on, the SW nodes will rise to VIN, and the voltage on the boot pin will be VCAP + VIN. The gate of the high side will have VCAP across it and it will be able to stay enhanced. A 0.1 F capacitor is a good value for this bootstrap element.
Co =
I OUT * dt _ I _ rise TR _ V _ dip
Transient Response percentage: TR_% (Use a recommended value of 2 to 4% to assure a good transient response.) Maximum Transient Voltage: TR_V_dip = VOUT*TR_% Maximum Current Step:
TYPE III COMPENSATION NETWORK
Power supplies are desired to offer accurate and tight regulation output voltages. A high DC gain is required to accomplish this, but with high gain comes the possibility of instability. The purpose of adding compensation to the internal error amplifier is to counteract some of the gains and phases contained in the control-to-output transfer function that could jeopardized the stability of the power supply. The Type III compensation network used for the 34717 comprises two poles (one integrator and one high frequency to cancel the zero generated from the ESR of the output capacitor) and two zeros to cancel the two poles generated from the LC filter as shown in Figure 9.
Iout _ step =
(Vin _ min - Vout ) * D _ max Fsw * L
Inductor Current Rise Time:
34717
Analog Integrated Circuit Device Data Freescale Semiconductor
21
TYPICAL APPLICATIONS
SWx VOUTx
5. Equating pole 2 to 5 times the Crossover Frequency achieves a faster response and a proper phase margin
Lx RSx CSx R1x COx
5 * F CROSS = F
INVx CXx COMPx
1 --------------------------------------P2 = CF CX 2 * R F ------------------CF + Cx
RFx CFx
R2x
CX =
CF 2 * R F C F FP 2 - 1
Figure 9. Type III compensation network 1. Choose a value for R1 2. Consider a Crossover frequency of one tenth of the switching frequency, set the Zero pole frequency to Fcross/10
TRACKING CONFIGURATIONS.
This device allows two tracking configurations: Ratiometric and Co-incidental Tracking.
FP 0
1 1 = FCROSS = 10 2 * R1C F
Vmaster
CF =
1 2 * R1 FPO
Different Slope
3. Knowing the LC frequency, the Frequency of Zero 1 and Zero 2 in the compensation network are equal to FLC
Vslave
FLC =
FZ 1 =
1 = FZ 1 = FZ 2 2 LX Co X
FZ 2 = 1 2 * R1C S
Figure 10. Ratiometric Tracking
1 2 * RF C F
Vmaster
This gives the result
Slave Regulation Point
RF =
1 2 * C F FZ 1
CS =
1 2 * R1 FZ 2
Same Slope Vslave
4. Calculate RS by placing the first pole at the ESR zero frequency
1 = FP1 2 * Co X * ESR 1 1 RS = FP1 = 2 * FP1C S 2 * RS C S FESR =
Figure 11. Co-incidental Tracking
RATIOMETRIC TRACKING CIRCUIT CONFIGURATION
The master voltage feedback resistor divider network is used in place of R3 and R4 as shown in Figure 12. The slave output is connected through its own feedback resistor divider network to the INV- terminal, resistors R1 and R2. All four
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22
Analog Integrated Circuit Device Data Freescale Semiconductor
TYPICAL APPLICATIONS
resistors will affect the accuracy of the system and must be 1% accurate resistors. To achieve this tracking configuration, the master voltage must be connected in the way shown and cannot be directly connected to the VREFIN terminal.
and R2 = R4 + R5). The master's feedback resistor divider would be (R3+R4) and R5. All five resistors will affect the accuracy of the system and must be 1% accurate resistors. To achieve this tracking configuration, the master voltage must be connected in the way shown and cannot be directly connected to the VREFIN terminal.
VMASTER
VMASTER
VBG
VREFIN
R3 R4
To INV- of Vmaster
VBG
VREFIN
R3 R4 To INV- of Vmaster
Reference selector
VSLAVE
Reference selector
R5
VSLAVE
Rs
EA +
R1 RF CF
INV
Cs CX R2
CO
EA +
Rs
INV
R1 RF CF
Cs CX R2
CO
COMP
COMP
Figure 12. Ratiometric Tracking Circuit Connections
Figure 14. Co-incidental Tracking Circuit Connections
EQUATIONS
* * * * VM = VBG_M(1+R3/R4) VREFIN = VM * R4/(R3+R4) VREFOUT = VREFIN VS = VREFOUT(1+R1/R2) = VM* R4/(R3+R4)*(R2+R1)/R2, if VREFOUT < VBG_S * VS = VBG_S(1+R1/R2), if VREFOUT VBG_S
EQUATIONS
VM = VBG_M[1+(R3+R4)/R5] VREFIN = VM*(R4+R5)/(R3+R4+R5) VREFOUT = VREFIN VS = VREFOUT(1+R1/R2) = VM*(R4+R5)/ (R3+R4+R5)*(R2+R1)/R2 = VM if VREFOUT < VBG_S * VS = VBG_S(1+R1/R2), if VREFOUT VBG_S * * * *
Figure 13. Ratiometric Tracking Plot
CO-INCIDENTAL TRACKING CIRCUIT CONFIGURATION:
Connect a three resistor divider to the master voltage (VM) and Route the upper tap point of the divider to the VREFIN terminal, resistors R3, R4, and R5 as shown in Figure 14. This resistor divider must be the same ratio as the slave output's (VS) feedback resistor divider, which in turn connects to the INV- terminal, resistors R1 and R2 below (Condition: R1 = R3
Figure 15. Co-incidental Tracking Plot Not-DDR Mode (Source Only Mode) is the case when no tracking is needed. VREFIN should be connected to VDDI and the reference selection block will use the internal band gap voltage as the error amplifier's reference voltage. A user can potentially apply a voltage to the VREFIN terminal directly or through a resistor divider to get a buffered output for use in the application. The condition here is, the voltage applied to the VREFIN terminal is greater than VBG to guarantee that the reference selection block will not switch back to the VREFOUT voltage.
34717
Analog Integrated Circuit Device Data Freescale Semiconductor
23
TYPICAL APPLICATIONS
LAYOUT GUIDELINES
The layout of any switching regulator requires careful consideration. First, there are high di/dt signals present, and the traces carrying these signals need to be kept as short and as wide as possible to minimize the trace inductance, and therefore reduce the voltage spikes they can create. To do this, an understanding of the major current carrying loops is important. See Figure 16. These loops, and their associated components, should be placed in such a way as to minimize the loop size to prevent coupling to other parts of the circuit. Also, the current carrying power traces and their associated return traces should run adjacent to one another, to minimize the amount of noise coupling. If sensitive traces must cross the current carrying traces, they should be made perpendicular to one another to reduce field interaction. Second, small signal components which connect to sensitive nodes need consideration. The critical small signal components are the ones associated with the feedback circuit. The high impedance input of the error amp is especially sensitive to noise, and the feedback and compensation components should be placed as far from the switch node, and as close to the input of the error amplifier as
VIN1
possible. Other critical small signal components include the bypass capacitors for VIN, VREFIN, and VDDI. Locate the bypass capacitors as close to the pin as possible. The use of a multi-layer printed circuit board is recommended. Dedicate one layer, usually the layer under the top layer, as a ground plane. Make all critical component ground connections with vias to this layer. Make sure that the power grounds, PGND1 and PGND2 are connected directly to the ground plane and not routed through the thermal pad or analog ground. Dedicate another layer as a power plane and split this plane into local areas for common voltage nets. The IC input supply (VIN) should be connected with a dedicated trace to the input supply. This will help prevent noise on the buck regulator's power inputs (PVIN1 and PVIN2) from injecting switching noise into the IC's analog circuitry. In order to effectively transfer heat from the top layer to the ground plane and other layers of the printed circuit board, thermal vias need to be used in the thermal pad design. It is recommended that 5 to 9 vias be spaced evenly and have a finished diameter of 0.3 mm.
PVIN1 and 2 VIN2 and 3
Loop Curr ent HS ON HS Loop Curr ent HS ON
HS SW1 SD
SW1 and 2 SW2 and 3
Loop Current SD ON LS GND2 and 3 PGND1 and 2 BUCK CONVERTER 1 Loop Current LS ON
Buck Converter 1 and 2 BUCK CONVERTER
2 and 3
Figure 16. Current Loop
34717
24
Analog Integrated Circuit Device Data Freescale Semiconductor
PACKAGING PACKAGING DIMENSIONS
PACKAGING
PACKAGING DIMENSIONS
EP SUFFIX (PB_FREE) 26-PIN QFN 98ASA10728D ISSUE 0
34717
Analog Integrated Circuit Device Data Freescale Semiconductor
25
PACKAGING PACKAGING DIMENSIONS
EP SUFFIX (PB-FREE) 26-PIN QFN 98ASA10728D ISSUE 0
34717
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Analog Integrated Circuit Device Data Freescale Semiconductor
REVISION HISTORY
REVISION HISTORY
REVISION 1.0 2.0
DATE 2/2006 1/2007
DESCRIPTION OF CHANGES * * * * * * * * * * * * * * * * * * * * * * * * * * * * Pre-release version Implemented Revision History page Initial release Converted format from Market Assessment to Product Preview Major updates to the data, form, and style Changed Feature fom 2% to 1%, relabeled to include soft start Change references for 45 m Integrated N-Channel Power MOSFETs to 50 m Removed Machine Model in Maximum Ratings Added Channel 1 High Side MOSFET Drain Voltage Range Changed Output Voltage Accuracy(12),(13) Changed Soft Start Adjusting Reference Voltage Range and Short-circuit Current Limit Changed High Side N-CH Power MOSFET (M4) RDS(ON)(12) and Low Side N-CH Power MOSFET (M5) RDS(ON)(12) Changed M2 RDS(ON) and PVIN1 Pin Leakage Current Added Channel 2 High Side MOSFET Drain Voltage Range Changed Soft Start Adjusting Reference Voltage Range Changed Short-circuit Current Limit Changed High Side N-CH Power MOSFET (M6) RDS(ON)(14) and Low Side N-CH Power MOSFET (M7) RDS(ON)(14) Changed M3 RDS(ON) and PVIN2 Pin Leakage Current Changed SD Pin Internal Pull-up Resistor Changed Channel 1 Soft Start Duration (Normal Mode), Over-current Limit Retry Timeout Period, and Output Under-voltage/Over-voltage Filter Delay Timer Changed Channel 2 Soft Start Duration (Normal Mode), Over-current Limit Retry Timeout Period, and Output Under-voltage/Over-voltage Filter Delay Timer Changed Oscillator Default Switching Frequency Changed PG Reset Delay and Thermal Shutdown Retry Timeout Period(21) Changed definition for Soft Start ADJUStment input (ILIM1, ILIM2) Changed drawings in 34717 Typical Application Changed table for Soft Start Adjustment Removed PC34717EP/R2 from the ordering information and added MC34717EP/R2 Changed data sheet status to Advance Information Made changes to Switching Node (SW1, SW2) Pins, BOOT1, BOOT2 Pins (Referenced to SW1, SW2 Pins Respectively), Output Under-voltage Threshold, Output Over-voltage Threshold, Both channels of High Side N-CH Power MOSFET (M4) RDS(ON)(12), Both channels of Low Side N-CH Power MOSFET (M5) RDS(ON)(12), Charge Device Model Added Machine Model (MM), Both channels of SW2 Leakage Current (Standby and Shutdown modes), Both channels of (Error Amplifier DC Gain(14), Error Amplifier Unit Gain Bandwidth(14), Error Amplifier Slew Rate(14), Error Amplifier Input Offset(14)) Fixed drawing for Type III compensation network Added pin 27 to Figure 3 and the 34717 Pin Definitions Added the section Layout Guidelines
3.0
5/2007
4.0
12/2007
*
*
* * *
34717
Analog Integrated Circuit Device Data Freescale Semiconductor
27
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MC34717 Rev 4.0 12/2008

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