DCAN-40 VSX60 VSX75 APPLICATION NOTES Barry Ehrman, Applicat

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DCAN-40 VSX60 VSX75 APPLICATION NOTES Barry Ehrman, Applicat

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DCAN-40
DCAN-40
VSX60 VSX75 APPLICATION NOTES
Barry Ehrman, Applications Engineer
VSX60 Series VSX75 Series Watt Watt, respectively, dual output converters with 18-36V (VSX60 only) 36-75V input models with 3.3VDC 5VDC outputs. VSX60 VSX75 converters packaged industry quarter-pak size 1.5" 2.3" 0.5" have typical efficiency 90%. following application information designed supplement product data sheet.
Additional Information Control Features
Remote On/Off Control VSX60 Series VSX75 Series equipped with primary on/off control increased system flexibility. input open-collector and/or CMOS open-drain compatible. standard model, primary on/off uses negative logic, which turns converter when logic signal applied (see common specifications threshold voltage levels). Figure illustrates typical external connections enable this function. connection made primary on/off terminal, converter will operate.
Figure Primary On/Off Connections addition there "-1" option VSX60 Series VSX75 Series (i.e. VSX60MD35-1) which allows converters operate positive logic. recommended control circuits would same Figure except input logic would reversed (i.e. input logic will turn converter input logic high will turn converter). connection made primary on/off terminal converter with "-1" option, converter will operate normally. Output Voltage Trim output voltage trim feature allows user accurately adjust converter's output voltage point specified level (see Table This achieved connecting resistor from TRIM terminal either (+3.3 Volt Output) (Output Return) pins. increased output voltage desired, resistor should connected between TRIM pins. decreased output voltage desired, external resistor should connected between TRIM pins. Figure illustrates required connections implement this feature. Connecting TRIM directly will trim converter down connecting TRIM directly will trim converter 10%. Please Note: When using Page
3400 Britannia Drive, Tucson, Arizona 85706
DCAN-40
output voltage "Trim" feature, both outputs will adjusted same direction same percentage.
TABLE RESISTOR (RUP) VALUES (KOHMS) DESIRED INCREASE OUTPUT VOLTAGE MODEL VSX60xS35 50.327 23.211 13.906 9.202 6.363 4.463 3.102 2.08 1.284
RESISTOR (RDOWN) VALUES (KOHMS) DESIRED DECREASE OUTPUT VOLTAGE MODEL VSX60xS35 67.116 29.512 17.358 11.35 7.767 5.388 3.692 2.423 1.438
Design Considerations
Current Limiting Each converter equipped with current-limiting circuitry designed provide continuous protection against fault short circuit conditions. current limit point typically 5%-25% above rated output current. When short circuit condition removed, output voltage will return "pre-short circuit" value without recycling input. Safety VSX60 Series VSX75 Series recognized conformance with UL/CUL1950 EN60950. output VSX60 VSX75 considered level output when supply converter meets SELV requirements (VIN 60VDC). Fusing Requirements VSX60 Series VSX75 Series converters internally fused. order maintain maximum safety overall system protection, input line fuse should always included. normal blow D.C. fuse with maximum rating recommended. Input Source Impedance converter should connected impedance input source ensure system stability. recommended that small electrolytic capacitor with (eg. input models (M), 0.14 input models (L)) should placed across input terminals close module possible maintain unit stability.
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DCAN-40
Test Circuit Configurations
Figure Measurement Input Reflected Ripple
Figure Measurement Input Reflected Ripple with External Reduction Circuit
Figure Measurement Peak Peak Output Noise
Circuit Configuration Designed Minimize Conducted
Minimizing conducted from switching converter sometimes challenge. VSX60 VSX75 filter circuit shown Figure circuit layout Figure designed simplify this challenge. This circuit used most applications with little modification meet most requirements.
Figure Filter Circuit Page
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DCAN-40
Figure Circuit Layout Filter
following components recommended Circuit Figures
3400 Britannia Drive, Tucson, Arizona 85706
C11,
Normal Blow Fuse 0.68 Metallized Polyester Film Capacitors 1000 Ceramic Type 1500V Capacitors 1500 Volt Ceramic Capacitors Volt Ceramic Type Capacitors Volt Ceramic Type Capacitors Volt ESR, Electrolytic Capacitor Common-mode Inductor, Pulse P0351 equivalent surface mount resistors (application dependent) Page
DCAN-40
Figure actual graphs from spectrum analyzer showing conducted from fully loaded VSX60MS35 when used conjunction with recommended board layout suggested components. limit lines graphs CISPR Class Quasi Peak emission limits.
Figure VSX60 Conducted Using Recommended Board Layout Components
Thermal Considerations
VSX60 Series VSX75 Series products designed operate with baseplate temperature between degrees +100 degrees baseplate temperature should rise above +100 degrees internal heat generation, Over Temperature Protection (OTP) circuit will turn converter prevent damage. unit will turn itself back when baseplate temperature drops below degrees actual shutdown temperature between degrees case. avoid Page
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DCAN-40
unexpected shutdown, important always keep baseplate temperature below degrees This done first calculating case temperature under worst case conditions determine additional airflow, heatsink both maybe required.
Thermal Equations
order calculate case temperature particular application, following thermal equations will prove useful:
Efficiency Power) Dissipated Power (Power Lost) {(1- Temperature Rise POUT {(1-
Normalized Efficiency Charts
following charts used more precisely predict expected efficiency VSX60 VSX75:
NORMALIZED EFFICIENCY TOTAL OUTPUT LOAD
1.0200 1.0000 Normalized Efficiency 0.9800 0.9600 0.9400 0.9200 0.9000 0.8800 0.8600 0.8400 0.8200 0.8000 Total Load Rated
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=Thermal Resistance from Base Ambient) Maximum Output Power {TBASE (max) BA{(1- (TBASE (max) Maximum BaseTemperature degrees Ambient Temperature) Minimum Thermal Impedance {TbASE (max) TA}/[POUT{(1-
DCAN-40
NORMALIZED EFFICIENCY LOAD DISTRIBUTION
1.0050 Normalized Efficiency 1.0000 0.9950 0.9900 0.9850 0.9800 0.9750 0.9700 0.9650 0.9600 100%/0% 75%/25% 50%/50% 25%/75% 0%/100%
LOAD% (3.3V
NORMALIZED EFFICIENCY INPUT VOLTAGE
1.005 1.000 Normalized Efficiency 0.995 0.990 0.985 0.980 0.975 0.970 0.965 0.960 0.955 Input Voltage (Volts)
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DCAN-40
NORMALIZED EFFICIENCY BASEPLATE TEMPERATURE
1.0020 1.0010 Normalized Efficiency 1.0000 0.9990 0.9980 0.9970 0.9960 0.9950
Degrees Celsius
Thermal Impedance
ERMAL IMPEDANCE WITHOUT HEATSINK
Flow
Without Mechanical
BA(De With Mechanical Down**
**Mechanically tied down through PEMS with steel screws layer FR4. ground plane contains 11.75 copper ground plane contains copper. steel screws shall applied from baseplate side converter washer shall used make electrical connection ground plane. Applying screws from side converter will void converter's warranty.
following example will illustrate calculate baseplate temperature under specific operating conditions: Example: customer application that requires VSX60MD35 drive load watts cabinet degrees with linear feet minute flow. input voltage will typically Volts under some conditions rise Volts. load current VSX60MD35 will distributed between Volt output Volt output follows: Volt load current Amps Volt load current Amps order determine baseplate temperature VSX60MD35, amount heat generated must determined. Heat generated converter caused inefficiency converter
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DCAN-40
called "Dissipated Power". efficiency VSX60MD35 with Watt load, under stated conditions, calculated follows:
Where:
Minimum Efficiency VSX60MD35 from data sheet Efficiency adjustment factor based graph Normalized Efficiency Input
Voltage
Efficiency adjustment factor based graph Normalized Efficiency adjustment factor based graph Normalized
Because efficiency defined Power-Out (POUT) divided Power-In (PIN) times 100%, Dissipated Power (PD) calculated follows: Efficiency/100% POUT (VOUT IOUT)/(VIN IIN) Dissipated Power POUT {(1- {(1-0.8838)/0.8838} Dissipated Power 6.968 Watts Next, temperature rise baseplate determined multiplying thermal resistance from base plate ambient which found Thermal Impedance chart page times Dissipated Power. knowing temperature rise baseplate, worst case temperature baseplate determined adding ambient temperature which shown follows:
Temperature baseplate =TBP 52.19 102.19 degrees With baseplate temperature 102.19 degrees converter will operate outside specified temperature range. There several ways solve this problem: drop thermal resistance from baseplate ambient; reduce output power; lower maximum ambient temperature. thermal resistance reduced blowing additional over converter; adding heat sink; both. following equations used calculate maximum output power that delivered maximum thermal resistance converter tolerate. maximum thermal resistance then used conjunction with Thermal Impedance Chart page determine correct combination flow heat sink. Note: combination chart should have lower thermal resistance than maximum calculated. this example, nothing else changed, maximum output power would have reduced using Equation page follows: Maximum Output Power {Tbaseplate (max) {(1- Maximum Output Power (95-50)/[7.49 {(1-0. 0.8838/0.8838)}] Note: degrees used instead degrees degrees margin. Maximum Output Power 45.6 Watts
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Temperature Rise=
POUT
Efficiency
(.89) (.997) (1.00) (.996) 88.38%
Efficiency Total Output Load Efficiency Load Distribution
{(1- 6.968 7.49 52.19 degrees
DCAN-40
this example, thermal Impedance changed, Equation page used calculate required Maximum Thermal Impedance follows:
seen looking thermal impedance charts page page this example would require Linear Feet Minute (LFM) airflow with heat sink VSX60 VSX75 with HSK-VSX heat sink Linear Feet Minute (LFM) airflow. Power Derating Information
following graphs show alternative) power derating VSX60 VSX75 function ambient temperature flow:
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Maximum Thermal Impedance Maximum Thermal Impedance Maximum Thermal Impedance
{Tbaseplate (max) TA}/[POUT{(1- (95-50)/ {(1-0. 0.8838/0.8838)}] 6.458 Degrees Watt
DCAN-40
POWER DERATING VERSIONS (Unencapsulated)
Output Load 3.3V Output) Ambient Temperature (TA) (VSX60MD35-U Mechanical Tiedown)
3.3V Output
Flow
(Deg
Output Load 5.0V Output) Ambient Temperature (TA) (VSX60MD35-U Mechanical Tiedown)
5.0V Output
Flow
(Deg
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DCAN-40
Output Load (I1+I2) Ambient Temperature (TA) (VSX60MD35-U Mechanial Tiedown)
50.0
I1+I2 full load each outputs)
40.0 Flow 30.0 20.0
10.0
(Deg
Output Load 3.3V Output) Ambient Temperature (TA) (VSX75MD35-U Mechanical Tiedown)
3.3V Output
Flow
(Deg
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DCAN-40
Output Load 5.0V Output) Ambient Temperature (TA) (VSX75MD35-U Mechanical Tie-down)
5.0V Output
Flow
(Deg
Output Load (I1+I2) Ambient Temperature (TA) (VSX75MD35-U Mechanical Tiedown)
50.0
I1+I2 full load each outputs)
40.0
30.0
Flow Series1
20.0
10.0
(Deg
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DCAN-40
Recommended Accessories
Following drawing heat sink HSVSX from Technologies which been designed used with VSX60 VSX75 families products.
Thermal Impedance* (Deg Flow C/Watt) With Heat sink HSVSX Free 8.54 5.14 3.49 2.82 2.57 1000 2.23 *Thermal impedance includes thermal impedance degree Watt thermally conductive interface material between VSX60 VSX75 baseplate heat sink.
KIT*/PART
HEAT SINK INCLUDED
OVERALL PACKAGE HEIGHT**
HSK-VSX
HSVSX
0.75"
omplete lude four mounting rews prec thermal interfac material prov improv thermal onduc from erter heat erall height ludes 0.01" height interfac pad.
Technologies tries maintain reasonable stock above heatsink kit. Please either contact factory authorized distributors price availability
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DCAN-40
answers questions information contained this application note, please contact Technologies, Applications Group, phone (520) 295-4104, (520) 295-4197, Email swood@cdtechno.com. write address shown below.
HISTORY CHANGES Fusing page changed from filter changed pages filter changed pages thermal example added pages 8-11. Various corrections grammar Added page recommended method mechanical down ground plane. Changed grounding recommendations page under "Safety" Updated Applications group Email Address page Added VSX75 Series throughout Note. Changed Safety Agency Nomenclature page Changed Normalized Efficiency Graph page Changed both Power Derating Graphs page address contact information Page Added Derating Graphs Unencapsulated VSX60 Pages 10-13.
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DCAN-40 VSX60 VSX75 APPLICATION NOTES Barry Ehrman, Applicat

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