PRODUCT DATA SHEET PLANAR POWER TRANSFORMER Features Applications ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ Planar windings 4mm height above PCB Low leakage inductance High frequency operation Externally configurable Centre-tapped secondaries Lead-free (Pb-free) P6141 DC-DC converters Forward converters 48V or 24V inputs 5V @ 5A output 3.3V @ 7A output DESCRIPTION P6141 is a planar power transformer using multilayer PCB technology. It is intended for low profile high frequency DC-DC forward converters up to 500kHz. With careful design, output power exceeding 30W is achievable. P6141 has split primaries and secondaries enabling the device to be configured for 48V and 24V inputs and 5V or 3.3V outputs. ETALDOC 856/3 Page 1 of 5 The contacts to the host circuit board are made by solder connection to large plated-through holes in the P6141 PCB, thus ensuring low resistance connection. The ferrite is intended to sit within a PCB cut-out, giving a height above board of 4mm. P6141 is lead-free (Pb-free) and suitable for conventional and lead-free processing. August 2004 P6141 SPECIFICATIONS Electrical Typical values at T = 25ºC, unless otherwise stated. Parameter Conditions Min Typ Max Units 17 25 35 µH - - 100 nH 500 - - Vrms Primary Inductance 100kHz, 100mV Each primary winding 2-9, 1-10 Leakage Inductance 500kHz, 100mV (1, 2) – (9, 10) link 3, 4, 5, 6, 7, 8 Primary/Secondary voltage isolation (1+2):3 Interwinding capacitance 100kHz, 1V primary : secondary - 308 - pF Total transformer losses Vout = 5V at Iout = 5A or Vout = 3.3V at Iout = 7A 400kHz - 0.7 - W DCR Primaries 2-9, 1-10 17 20 23 mΩ 3-5, 6-8 - 7.5 - mΩ Turns Ratio (1-10):(2-9) (5-3):(8-6) (1-10):(5-3) (2-9):(8-6) - 1.0 1.0 1.5 1.5 - - Operating range: Functional Storage Ambient temperature -40 -40 - +85 +85 ºC ºC Typical Magnetic Core Coefficients C1 Core factor Transformer sc hematic -1 0.514mm Fig 1 3 Ve Effective volume le Effective length Ae Effective area µe m Effective permeability 39.5mm 1270 Mass 4.1g 1 800mm 20.3mm PRIMARY 3T 4 1T 2 10 PRIMARY 8 3T 1T 7 1T Page 2 of 5 SECONDARY 3 2 9 ETALDOC 856/3 5 1T SECONDARY 6 August 2004 P6141 CONSTRUCTION Dimensions Connections Fig 3 25.0 12.0 9.8 19.2 5 PCB c utout 7.9 4 CORE Mounting pads: plated through holes ø1.5 11.7 10.0 2.1 7.0 4.2 CYYMM 7.7 18.0 9.8 7.0 6 3 1 2 9.8 Pin 1 ident 12.0 7 7.9 8 P6141 10 9 Cu PADS 2.0 x 2.4 (10x) R1 . 4.2 Fig 2 20 6.0 RECOMMENDED PCB LAYOUT (TOP VIEW) Dimensions shown are in millimetres. Terminal finish is 0.1µm max gold (Au) over nickel (Ni). APPLICATION SCHEMATICS P6141 is designed for forward converter applications where power is coupled from the primary to secondary circuits during the ‘on’ time of the switch. Unlike the flyback converter, the forward converter transformer is not designed as a storage element, and thus the ferrite core is ungapped. In the single quadrant operation forward converter, some means must be provided to ‘reset’ the flux due to the build up of magnetizing current in the device, and since P6141 does not have a reset winding, this function must be provided externally. There are several methods for providing the reset function in the absence of a reset winding. The first, shown in fig 4, uses a zener diode to perform the reset function. This has the advantage of simplicity; however, energy is wasted in the reset circuit, and there is a constraint on the duty cycle that must be observed. An alternative circuit is shown in fig 5, where two synchronized switches are used. This has the advantage that energy is returned to the supply; however, the duty factor is limited to 0.5. Forward converter with zener diode reset Fig 5 Fig 4 + SWITCH LOAD + V in – Vz – + + V in LOAD – SWITCH – SWITCH Note: Vz toff > Vin ton for flux to be fully reset ETALDOC 856/3 Page 3 of 5 August 2004 P6141 Input voltage setting For 48V operation, the P6141 primaries are connected in series, giving a nominal inductance of 100µH and primary DCR 41mΩ. For 24V operation, the primaries are connected in parallel, giving a nominal primary inductance of 25µH and primary DCR of 10mΩ Output voltage setting For 5V output, the P6141 secondaries are connected in series, giving a secondary DCR of 15mΩ. For 3.3V operation, the secondaries are connected in parallel, giving a secondary DCR of 3.8mΩ. Figs 6-9 show forward converter topologies with input voltages 48V and 24V and output voltages 5V and 3.3V. 48V input, 5V output 48V input, 3.3V output Fig 6 Fig 7 1 5 1 4 + 48V – 10 2 3 8 7 9 4 + + 5V – 48V – 10 3 2 8 7 6 9 24V input, 5V output 24V input, 3.3V output Fig 8 Fig 9 1 1 5 24V – 10 2 3 8 7 9 + 3.3V – 6 5 4 4 + 5 + + 5V – 6 24V – 10 3 2 8 7 9 + 3.3V – 6 For frequencies from 300—500kHz and output currents from 1–5A (5V output) and 1.5–7A (3.3V output) suitable low profile output inductors (height 4mm) can be found in the ETAL P7602-1003 range. See below for choice of output inductor. ETALDOC 856/3 Page 4 of 5 August 2004 P6141 Output inductor Unless they are current fed, forward converters require output inductors. Suitable standard power inductors are available from the ETAL range. The inductor must satisfy a number of criteria (apart from mechanical considerations) as follows:1. Minimum inductance. It is essential that the current through the inductor does not fall to zero, which places a constraint that the pk-pk ripple current must not exceed twice the minimum output current. Once the minimum output current (Iout) is defined, the minimum inductance (Lmin) as a function of frequency (f) and output voltage (Vout) can be defined thus: Lmin ≈ 0.3Vout Iout (min) f 2. Energy storage. The inductor must be able to store sufficient energy without saturation. Energy storage is given by: ½LI 2 out Profec publishes application data on its ETAL inductors showing, by product family, typical inductance ranges and storage energies. As a check, it is worth verifying from individual datasheets that maximum current (maximum load current + ripple current) does not exceed the saturation current rating. As an example, for the 5V/5A output and minimum output current of 1A with switching frequency 400kHz, the minimum inductance calculated is 3.75µH and energy storage requirement 47µJ. A low profile (4mm) shielded power inductor P7602-1003-3R8Y will be suitable. It has the following characteristics: L= 3.8µH Isat = 6A Energy = 68.4µJ ORDERING CODE ABSOLUTE MAXIMUM RATINGS (Ratings of components independent of circuit). P6141T Tape and Reel (400 parts per 13” reel) Type code Short term isolation voltage (1s) 500Vrms V.µs per primary winding 16V.µs Storage temperature +85ºC Magnetic Core temperature 120ºC Reflow temperature (10s) 260ºC (for ΔB=135mT) ETAL Group Oy, Kuormatie 14, FIN-03101, Nummela Telephone: +358 (0)20 7500 330 Fax: +358 (0)20 7500 333 Website: www.etalgroup.com Email: [email protected] ETALDOC 856/3 Page 5 of 5 ISO 9001 FM 25326 August 2004