ISL8500EVAL2Z Negative Output Buck-Boost Converter ISL8500EVAL2Z

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ISL8500EVAL2Z Negative Output Buck-Boost Converter ISL8500EVAL2Z

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Application Note 1500
ISL8500EVAL2Z Negative Output Buck-Boost Converter
ISL8500EVAL2Z intended individuals with requirements Point-of-Load applications sourcing from 14V. ISL8500EVAL2Z evaluation board used demonstrate performance ISL8500 standard buck-boost regulator. ISL8500 offered 4mmx3mm package with maximum height. complete converter occupies less than 0.385in2 area. Digital Multimeters (DMMs) 100MHz quad-trace oscilloscope Signal generator
Author:
electronic load capable sinking current
Quick Set-up Guide
Ensure that circuit correctly connected supply loads prior applying power. Connect bias supply VIN, plus terminal (VIN) negative return (GND). Verify that ENABLE. Turn power supply. Verify output voltage 2.5V VOUT(TP3).
Features
Standard Buck Controller with Integrated Switching Power MOSFET Integrated Boot Diode Input Voltage Range Variable to14V Output Voltage Adjustable from -12.6V -0.6V with Continuous Output Current Voltage Mode Control with Voltage Feed Forward Fixed 500kHz Switching Frequency Externally Adjustable Soft-Start Time Output Undervoltage Protection PGOOD Output Overcurrent Protection Thermal Overload Protection Internal regulator
Evaluating Other Output Voltage
ISL8500EVAL outputs preset -12V; however, programmed using resistor dividers using Equation
0.6V 0.6V (EQ.
output voltage programming resistor will depend feedback resistor referred Figure value typically between 10k. output voltage desired 0.6V, then left opened.
Applications
General Purpose Hand-Held Instruments
0.6V REFERENCE
What's Inside
Evaluation Board contains following materials: ISL8500 EVAL2Z Board ISL8500 Datasheet This EVAL Document
-VOUT
FIGURE EXTERNAL RESISTOR DIVIDER TABLE SWITCH SETTINGS ENABLE OPERATING MODE Enable disable buck controller
Recommended Equipment
following materials recommended perform testing: power supply with least source current capability, battery, notebook adapter
November 2009 AN1500.0
CAUTION: These devices sensitive electrostatic discharge; follow proper Handling Procedures. 1-888-INTERSIL 1-888-468-3774 Intersil (and design) registered trademark Intersil Americas Inc. Copyright Intersil Americas Inc. 2009. Rights Reserved other trademarks mentioned property their respective owners.
Schematic
2.43K
5.11K
0.01UF
150PF
2200PF
10UF
10UF
220UF
TP16
1.05K
2N7002
-VOUT PHASE BOOT
COMP -VOUT -VOUT
COMP
47UF
10UF
0.1UF
BOOT
100UF
-VOUT
ISL8500IRZ
TP13
100K
-VOUT
-VOUT
PHASE PHASE
Application Note 1500
-VOUT -VOUT
OPEN
POPULATE ONLY
AN1500.0 November 2009
Application Note 1500
ISL8500EVAL2Z Bill Materials
PART NUMBER ISL8500EVAL2ZREVAPCB REFERENCE UNITS DESIGNATOR DESCRIPTION PWB-PCB, ISL8500EVAL2Z, REVA, ROHS C10, CAP, SMD, 0402, 10nF, 50V, 10%, X7R, ROHS CAP, SMD, 1206, 10µF, 25V, 10%, X5R, ROHS MFTR TITAN MANUFACTURER PART ISL8500EVAL2ZREVAPCB
H1044-00103-50V10-T H1065-00106-25V10-T H1082-00476-16V20-T
PANASONIC VENKEL
ECJ-0EB1H103K C1206X5R250-106KNE
C13, C20, POPULATE PURCHASE CAP, SMD, 1210, 47µF, 16V, 20%, X5R, ROHS PANASONIC C3225X5R1C476M ECJ-4YB1E476M 1210YD476MAT C0402COG500-151JNE ECJ-0EB1H222K C0402X74500-471KNE ECJ1VB0J105K C1608X7R1H104K B340LB-13-F
H1044-00151-50V5-T H1044-00222-50V10-T
CAP, SMD, 0402, 150pF, 50V, NPO, ROHS CAP, SMD, 0402, 2200pF, 50V, 10%, X7R, ROHS CAP, SMD, 0603, 1µF, 6.3V, 10%, X5R, ROHS CAPACITOR, SMD, 0603, 0.10µF, 50V, 10%, DIODE-SCHOTTKY SMD, SMB, 40V, ROHS POPULATE PURCHASE
VENKEL PANASONIC VENKEL PANASONIC DIODES INC.
H1045-00105-6R3V10-T C1608X7R1H104K-T B340LB-13-F-T
C4,C8
IHLP2525CZRZ220M01
COIL-PWR INDUCTOR, SMD, 6.9x6.5, 22µH, 20%, 2.5A, ROHS POPULATE PURCHASE RES, SMD, 0402, 5.11k, 1/16W, ROHS RES, SMD, 0402, 100k, 1/16W, ROHS RES, SMD, 0402, 20k, 1/16W, ROHS POPULATE PURCHASE RES, SMD, 0603, 10k, 1/10W, ROHS RES, SMD, 0402, 698, 1/16W, ROHS
VISHAY
IHLP2525CZRZ220M01
H2510-05111-1/16W1-T
PANASONIC VENKEL PANASONIC PANASONIC VENKEL
ERJ-2RKF5111X CR0402-16W-5111FT ERJ2RKF1003 ERJ-2RKF2002 CR0402-16W-2002FT
H2510-01003-1/16W1-T H2510-02002-1/16W1-T
H2511-01002-1/10W1-T
VENKEL PANASONIC VENKEL
RK73H1JT1002F CR0603-10W-1002FT ERJ-2RKF6980X CR0402-16W-6980-FT
H2510-06980-1/16W1-T
AN1500.0 November 2009
Application Note 1500
ISL8500EVAL2Z Bill Materials (Continued)
PART NUMBER H2511-DNP H2510-01051-1/16W1-T REFERENCE UNITS DESIGNATOR DESCRIPTION RES, SMD, 0603, DNPPLACE HOLDER, ROHS RES, SMD, 0402, 1.05k, 1/16W, ROHS VENKEL PANASONIC VISHAY/DALE 131-4353-00 SP1, CONN-SCOPE PROBE TEST COMPACT, MNT, ROHS SWITCH-TOGGLE, SMD, ULTRAMINI, SPST MINI CONN-MINI TEST POINT, VERTICAL, WHITE, ROHS CONN-TURRET, TERMINAL POST, ROHS IC-2A BUCK REGULATOR, 12P, DFN, 4x3, ROHS TEKTRONIX CR0402-16W-1051FT ERJ-2RKF1051X CRCW04021K05FKED 131-4353-00 MFTR MANUFACTURER PART
GT11MSCBE-T
COMPONENTS KEYSTONE KEYSTONE
GT11MSCKE
5002 1514-2
TP13, TP16 TP1-TP4
5002 1514-2
ISL8500IRZ
INTERSIL
ISL8500IRZ
AN1500.0 November 2009
Application Note 1500
ISL8500EVAL2Z Board Layout
FIGURE COMPONENTS
AN1500.0 November 2009
Application Note 1500
ISL8500EVAL2Z Board Layout
(Continued)
FIGURE LAYER ETCH
AN1500.0 November 2009
Application Note 1500
ISL8500EVAL2Z Board Layout
(Continued)
FIGURE LAYER ETCH
AN1500.0 November 2009
Application Note 1500
ISL8500EVAL2Z Board Layout
(Continued)
FIGURE LAYER ETCH
AN1500.0 November 2009
Application Note 1500
ISL8500EVAL2Z Board Layout
(Continued)
FIGURE BOTTOM LAYER ETCH (Mirrored)
AN1500.0 November 2009
Application Note 1500
Theory Operation
ISL8500 this configuration non-sysnchronous positive negative switching regulator which handle input voltages above, below, equal absolute value output. ISL8500EVAL2Z circuit design optimized input -12V output applications. regulator operates 500kHz fixed switching frequency, under heavy load conditions allow smaller external inductors capacitors used minimal printed-circuit board (PCB) area. light load, regulator reduces switching frequency skipping pulses maintain regulation increase efficiency. principle operation shown Figure uses energy storage inductor during period, then transfers energy through free wheeling diode, output. When MOSFET switch turns diode reverse biased, inductor current will ramp When switch off, shown Figure inductor will reverse polarity maintain peak current. forward biased diode stored energy inductor gets transferred load output capacitor. Since voltage inductor negative with respect GND, output voltage across capacitor will negative. This type converter step down magnitude input voltage. Therefore, this circuit called buck-boost converter. steady state operation, volt-second inductor must equal, DVL= (1-D)VL. equal during time equal -VOUT during time. Therefore, steady state transfer VOUT/VIN -D/(1-D). Figure voltage current waveforms.
COUT
-VOUT
DURING TIME FIGURE VOLTAGE ACROSS ELEMENT DURING TIME
Equation Figure
(EQ.
VOUT ILAVE
VIN+VOUT
VIN+VOUT
-VOUT COUT
DURING TIME
FIGURE SIMPLIFICATION BUCK BOOST CONVERTER
FIGURE VOLTAGE ACROSS ELEMENT DURING TIME
Equation Figure
Equation Figure
LAVE (EQ.
(EQ.
AN1500.0 November 2009
Application Note 1500
Component Selection
This section will detail calculation selection components. Calculations done continuous operation mode.
47µF ceramic this example.
Input Capacitor Selection
main functions input capacitor provide decoupling parasitic inductance provide filtering function prevent switching current flowing back battery rail. 10µF ceramic capacitors good starting point input capacitor selection. capacitor connecting from -VOUT another connecting from GND.
Inductor Selection
From Equation ignoring diode rDS(ON) FET, duty cycle shown Equation
(EQ.
this example, 12V/(12V+12V) 0.5. average inductor current shown Equation
LAVE (EQ.
Compensation Selection
buck-boost typology difficult stabilize because right-half-plane zero control output transfer function. small signal model buck-boost power section relationship d(s) shown Figure
higher lower inductor value used optimize total converter system performance. example, higher output voltage application, order decrease inductor current ripple output voltage ripple, output inductor value increased. recommended ripple inductor current approximately maximum average inductor current optimized performance. inductor ripple current expressed shown Equation
LAVE (EQ.
VOUT
where switching frequency. inductor's saturation current rating needs least larger than peak current. ISL8500 protects typical peak current 3.1A. saturation current needs over maximum output current application. IOUT inductor 24µH. Then 22µH.
FIGURE SMALL SIGNAL MODEL
solve power transfer function, Equation
d(S) (EQ.11)
Diode Selection
free wheeling diode able handle maximum voltage current stress. voltage stress equal plus VOUT current stress ILAVE+0.5IL. power dissipation shown Equation
LAVE 0.5I
(EQ.
salent characteristics shown Equation
where forward voltage diode. This value typically 0.5V Schottky diode. B340LB good choice.
H(0)=33.8dB
Output Capacitor Selection
output capacitor selected based RESR value, capacitance must high enough hold charges load during time. output ripple shown Equation
LAVE 0.5I (EQ.
this RHPZ
43.4 (EQ.12)
8.77
where VOUT desired output ripple. minimum output capacitor value output ripple shown Equation
(EQ.10)
Q=18.9dB
FLC=2.4kHz
AN1500.0 November 2009
Application Note 1500
compensation network consists error amplifier (internal ISL8500) impedance networks. goal compensation network provide closed loop transfer function with highest crossing frequency (f0dB) adequate phase margin. From transfer function, there right-half-plane-zero. Therefore, highly recommended insure that crossover frequency, well before Figures bode plot gain phase H(S). Phase margin difference between closed loop phase f0dB 180°. Equation relates compensation network's poles, zeros gain components Figure following guidelines locating poles zeros compensation network: Pick Gain (R2/R1) converter bandwidth (~30% FZ).
GAIN (dB)
FREQUENCY (Hz)
FIGURE GAIN H(S)
Place Zero Filter's Double Pole.
Place Zero Below Filter's Double Pole (~30% FLC).
Place Pole half Switching Frequency.
PHASE
Place Pole 2.5x Zero. Check Gain against Error Amplifier's Open-Loop Gain.
Estimate Phase Margin Repeat Necessary.
Compensation Break Frequency Equations
FREQUENCY (Hz)
(EQ.
FIGURE PHASE H(S)
VOUT
Figures shows bode plot gain phase closed loop response.
ISL8500 REFERENCE
FIGURE DETAILED COMPENSATION NETWORK
GAIN (dB)
COMP
FREQUENCY (Hz)
FIGURE GAIN CLOSED LOOP
AN1500.0 November 2009
Application Note 1500
PHASE
compensation gain uses external impedance networks provide stable, high bandwidth (BW) overall loop. stable control loop gain crossing with -20dB/decade slope, phase margin greater than 40°. Include worst case component variations when determining phase margin.
FREQUENCY (Hz)
FIGURE PHASE CLOSED LOOP
Intersil Corporation reserves right make changes circuit design, software and/or specifications time without notice. Accordingly, reader cautioned verify that Application Note Technical Brief current before proceeding.
information regarding Intersil Corporation products, www.intersil.com
AN1500.0 November 2009
Application Note 1500
Typical Performace Curves
+25°C, Unless Otherwise Specified, operating conditions are: +25°C, 12V, VDD, 22µH, 100µF, 10µF, IOUT
POWER DISSIPATION
EFFICENCY
OUTPUT LOAD
OUTPUT LOAD
FIGURE EFFICIENCY LOAD
FIGURE POWER DISSIPATION LOAD
12.29 12.28 OUTPUT VOLTAGE OUTPUT VOLTAGE 12.28 12.27 12.27 12.26 12.26 12.25 12.25
12.290 12.285 12.280 12.275 12.270 0.5A 12.265 12.260 12.255 12.250 INPUT VOLTAGE
ISL8500 VOUT
OUTPUT LOAD
FIGURE VOUT REGULATION LOAD
FIGURE OUTPUT VOLTAGE REGULATION
PHASE 10V/DIV
PHASE 10V/DIV
VOUT RIPPLE 20mV/DIV 0.5A/DIV
VOUT RIPPLE 20mV/DIV
1A/DIV
FIGURE STEADY STATE OPERATION LOAD
FIGURE STEADY STATE OPERATION FULL LOAD
AN1500.0 November 2009
Application Note 1500
Typical Performace Curves
+25°C, Unless Otherwise Specified, operating conditions are: +25°C, 12V, VDD, 22µH, 100µF, 10µF, IOUT (Continued)
PHASE 10V/DIV
0.5V/DIV VOUT RIPPLE 100mV/DIV VOUT 0.5V/DIV
1A/DIV 1A/DIV
FIGURE LOAD TRANSIENT
FIGURE SOFT-START LOAD
VOUT 0.5V/DIV
0.5V/DIV
0.5V/DIV
VOUT 0.5V/DIV
1A/DIV
1A/DIV
FIGURE SOFT-START FULL LOAD
FIGURE SHUT-DOWN CIRCUIT
PHASE 10V/DIV
PHASE 10V/DIV
VOUT 5V/DIV VOUT 0.5V/DIV
1A/DIV
1A/DIV
FIGURE OUTPUT SHORT CIRCUIT
FIGURE OUTPUT SHORT CIRCUIT RECOVERY
AN1500.0 November 2009

ISL8500EVAL2Z Negative Output Buck-Boost Converter ISL8500EVAL2Z

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