AN10361 Philips BISS loadswitch solutions and the SOT666 BISS loadswitch demo board Rev. 01.00 — 20 June 2005 Application note Document information Info Content Keywords BISS, loadswitch, high side switch, supply line switch, SOT666, low VCEsat, RET Abstract This application note describes the Philips BISS loadswitch solutions using improved bipolar technology and the SOT666 BISS loadswitch demo board, complemented by selected measurement results. AN10361 Philips Semiconductors BISS loadswitch solutions Revision history Rev Date Description <01> <20050620> Initial document Contact information For additional information, please visit: http://www.semiconductors.philips.com For sales office addresses, please send an email to: [email protected] <12NC> Application note © Koninklijke Philips Electronics N.V. 2005. All rights reserved. Rev. 01.00 — 20 June 2005 2 of 12 AN10361 Philips Semiconductors BISS loadswitch solutions 1. Introduction After the introduction into different loadswitch solutions the demo board will be described and measurement results will be provided to allow the designer a more detailed view to the loadswitch performance. The SOT666 BISS loadswitch demo board is intended to be used for evaluation purpose of the PBLS1501V – PBLS1503V and PBLS4001V – PBLS4003V BISS Loadswitches in the SOT666 package. Evaluation results can also be used for the PBLS1501Y – PBLS1503Y and PBLS4001Y – PBLS4003Y BISS loadswitches in SOT363 (SC-88) due to the same electrical and thermal specification and internal die construction. 2. The loadswitch circuit A loadswitch – also referred to as high side switch or supply line switch – switches a supply voltage to a load or a supply line. It is used to drive fans, relays or motors, to switch sub-circuits like a mobile phone camera module or to build a voltage sequencing circuit. A digital signal switches the load switch ON or OFF. There are four alternatives to realize a loadswitch circuit as Fig 1 – Fig 4 show. Fig 1. This loadswitch circuit uses bipolar transistors Fig 2. Alternative circuit with a control N-MOSFET Fig 3. Alternative circuit with a pass P-MOSFET Fig 4. Alternative “pure” MOSFET solution <12NC> Application note © Koninklijke Philips Electronics N.V. 2005. All rights reserved. Rev. 01.00 — 20 June 2005 3 of 12 AN10361 Philips Semiconductors BISS loadswitch solutions The loadswitch circuit in Fig 1 consists of six components and uses bipolar transistors. If a positive voltage is applied to the base of the control transistor Tr2 through R1, it switches the pass transistor Tr1. A small base current of about a Milliampere switches up to a few Amperes. The voltage drop across collector and emitter of the pass transistor can be influenced by its base resistor R3. The lower R3, the higher Tr1’s base current and the lower the voltage drop, i.e. the saturation voltage. But, the higher the base current and the higher the input voltage the higher the power dissipation of this circuit, mostly through R3. Fig 2 - Fig 4 show circuit alternatives using MOSFET(s). Depending on cost and performance requirements each alternative has its advantages and disadvantages as Table 1: explains. Compared to MOSFET pass transistor alternatives the major advantage of solutions with a bipolar pass transistor are the far lower costs, the major disadvantage the higher power dissipation particularly for input voltages above 5 V due to the required base current for Tr1 (Ptot = PC = Pdrive = VCEsat x IC + Vin x IB). The PMOSFET circuits are the most expensive ones and typically require an additional Zener diode for ESD protection. Table 1: Cost and performance requirements determine the selection of loadswitch components Pass transistor Control transistor PNP bipolar NPN bipolar PNP bipolar N-MOSFET P-MOSFET NPN bipolar P-MOSFET N-MOSFET Reference figure Fig 1 Fig 2 Fig 3 Fig 4 Cost + cheap pass transistor + cheap control transistor + cheap pass transistor - expensive control transistor - expensive pass transistor + cheap control transistor - expensive pass transistor - expensive control transistor Power dissipation - fair - fair + low + low Control input current • low + no • low + no Threshold voltage + low - high + low - high Reverse blocking + yes + yes - no - no ESD sensitive + no + no - yes - yes 3. Bipolar transistor products for loadswitch applications Philips offers a wide variety of product alternatives to realize a loadswitch allowing to build a discrete, a partly integrated or a fully integrated solution. The widest flexibility and lowest voltage drop provides the discrete solution. The availability of various low VCEsat (BISS) transistors1 (PBSS-series) enables to select the best fitting transistor for the application. To limit the higher number of components the use of resistor-equipped transistors (RETs, PDTC-, PDTD-series) is recommended. These are standard transistors with built-in resistors making external resistors R1 and R2 obsolete. If the current to be switched is less than 100 mA and if there are no tight voltage drop requirements the number of components can be reduced to one if a double NPN/PNP RETs (PIMD-, PUMD-, PEMD-series) is used. The circuit parameter can be set be selecting the most appropriate type out of 13 different combinations of resistance values. 1. see also AN10116 “Breakthrough In Small Signal - Low VCEsat (BISS) Transistors and their Applications” <12NC> Application note © Koninklijke Philips Electronics N.V. 2005. All rights reserved. Rev. 01.00 — 20 June 2005 4 of 12 AN10361 Philips Semiconductors BISS loadswitch solutions A partly integrated solution features a low voltage drop and a reduced number of components. The BISS loadswitch contains a PNP low VCEsat (BISS) transistor as pass transistor and a NPN resistor-equipped transistor as control transistor in a 6pin package. The current portfolio (June 2005) includes 0.5 A and 1 A types with different breakdown voltages to meet different application requirements (e.g. VCEO = 60 V for automotive applications) and different integrated resistors to set the control transistor’s base current depending on the control input voltage. An external resistor (R3) is used to set the base current of the pass transistor. The voltage drop (= transistor’s saturation voltage) decreases with increasing base current, whereas the power dissipation of the loadswitch circuit increases. Table 2: summarizes the three alternatives of realizing a bipolar loadswitch circuit. Table 2: The partly integrated solution features a low voltage drop while the number of components could be reduced. Solution Discrete Partly integrated Fully integrated Component count 4–6 2–3 1 Voltage drop very low low higher Flexibility broadest portfolio ability to balance low saturation voltage vs. low base current large number of available types to meet application requirements Collector current (IC) 0.5 – 5 A 0.5 – 1 A 100 mA Breakdown voltage (VCEO) 15 – 100 V 15 – 60 V 50 V Types PBSS-series (pass transistor) PDTC-, PDTD-series (control transistor) PBLS-series PIMD-, PUMD-, PEMD-series 4. The SOT666 BISS loadswitch demo board The SOT666 BISS loadswitch demo board contains six loadswitch circuits as shown in Fig 5 – Fig 7. Each of the six circuits contains the BISS loadswitch Q – which includes the PNP pass transistor, the NPN control transistor and its two associated resistors – and two resistors R1 and R2 in size 0603. Additional space is given for optional 1206 sized input and output capacitors C1 and C2. The top row contains the 15 V types PBLS1501V through PBLS1503V whereas the bottom row is assembled with the 40 V types PBLS4001V through PBLS4003V. The difference between PBLSxx01V – PBLSxx03V types is the value of the internal resistors of the control transistor. Table 3: contains the bill of material for the full board. The connection of the demo board is done by soldering wires from the related pad to the application circuit or test setup. Grooves allow to break the circuit into single loadswitch circuits which simplifies their use in the final application. <12NC> Application note © Koninklijke Philips Electronics N.V. 2005. All rights reserved. Rev. 01.00 — 20 June 2005 5 of 12 AN10361 Philips Semiconductors BISS loadswitch solutions Fig 5. The SOT666 BISS loadswitch demo board Fig 6. Demo board layout Fig 7. Demo board circuit Table 3: Bill of materials Part reference Qty Type, Value Package Vendor Remark Q 1 PBLS1501V (2k2 / 2k2) SOT666 Philips 1 PBLS1502V (4k7 / 4k7) Counted from the top left to the bottom right 1 PBLS1503V (10k / 10k) 1 PBLS4001V (2k2 / 2k2) 1 PBLS4002V (4k7 / 4k7) 1 PBLS4003V (10k / 10k) R1 1 220R 0603[1] R2 1 10k 0603 C1, C2 [1] 1206 not mounted Note: R1 of the bottom right loadswitch circuit is 1206 sized to improve power dissipation capability <12NC> Application note © Koninklijke Philips Electronics N.V. 2005. All rights reserved. Rev. 01.00 — 20 June 2005 6 of 12 AN10361 Philips Semiconductors BISS loadswitch solutions 5. Measurement results This chapter discusses selected test results. Measurements were done for the 40 V-type PBLS4001V and the 15 V-type PBLS1501V. The internal resistance values are 2.2 kΩ for both types. Opposed to the demo board configuration described above, R1 was set to 100 Ω, 220 Ω and 470 Ω, respectively. R2 was kept open. Table 4: through Table 6: contain the measured values. The following paragraphs reflect the outcome. BISS loadswitches with a lower breakdown voltage (VCEO) feature a lower voltage drop and power dissipation. Comparing the 40 V PBLS4001V and the 15 V PBLS1501V (Table 4: and Table 6:) results in VCEsat = 214 mV, PC = 88 mW compared to VCEsat = 127 mV, PC = 52 mW of the latter one. As a guidance the user should select the lowest possible VCEO value. The lower the forced current gain IC/IB the lower the voltage drop VCEsat. Table 5: exemplarily shows that VCEsat decreases from 159 mV to 127 mV if IC/IB decreases from 46 to 10. In turn, the circuit needs more drive power (Pdrive = Vin x IB) which reduces the efficiency. As a consequence the user needs to balance voltage drop and acceptable power dissipation by selecting R1. If the Vdrop requirement can not be met by using a 500 mA BISS loadswitch the 1 A versions in SOT457 (SC-74) with lower saturation voltage values might be an alternative (see Table 7: below). The collector-emitter saturation resistance depends on the collector current. Opposed to the RDS(on) of MOSFETs the RCEsat of bipolar transistors depends on the collector current. This can be seen in Table 6: where RCEsat decreases with increasing collector current operating with constant forced current gain IC/IB. The total power dissipation sums up from drive and collector power dissipation. As Fig 9 shows the total power dissipation Ptot can be reduced by reducing the drive power dissipation Pdrive, i.e. the PNP transistor’s base current. However, the saturation voltage increase – indicated by the increasing collector power dissipation PC – must be watched to meet the Vdrop requirement. If the 500 mA PBLS-series is not sufficient, check the 1 A PBLS-series (see Table 7: below). Vdrop = VCEsat mW 300 IB 250 200 150 Pdrive 100 Rint PC 50 0 100R Rint Fig 8. Parameter definition for chapter 5 470R PBLS1501V Fig 9. Total power dissipation as a result of drive power dissipation Pdrive and collector power dissipation PC <12NC> Application note 220R © Koninklijke Philips Electronics N.V. 2005. All rights reserved. Rev. 01.00 — 20 June 2005 7 of 12 AN10361 Philips Semiconductors BISS loadswitch solutions Table 4: PBLS4001V, IC/IB = constant VCEO = 40 V, Rint = 2.2 kΩ, R2 = open IC VCEsat RCEsat IB IC/IB R1 PC Ptot 412 mA 214 mV 519 Ω 41 mA 10 100 Ω 88 mW 293 mW 232 mA 133 mV 573 Ω 19 mA 12 220 Ω 31 mW 126 mW 105 mA 72 mV 686 Ω 9 mA 11 470 Ω 8 mW 53 mW Table 5: PBLS1501V, IC = constant VCEO = 15 V, Rint = 2.2 kΩ, R2 = open IC VCEsat RCEsat IB IC/IB R1 PC Ptot 412 mA 127 mV 308 Ω 41 mA 10 100 Ω 52 mW 257 mW 412 mA 140 mV 340 Ω 19 mA 22 220 Ω 58 mW 153 mW 412 mA 159 mV 386 Ω 9 mA 46 470 Ω 66 mW 111 mW Table 6: PBLS1501V, IC/IB = constant VCEO = 15 V, Rint = 2.2 kΩ, R2 = open IC VCEsat RCEsat IB IC/IB R1 PC Ptot 412 mA 127 mV 308 Ω 41 mA 10 100 Ω 52 mW 257 mW 232 mA 77 mV 332 Ω 19 mA 12 220 Ω 18 mW 113 mW 105 mA 39 mV 371 Ω 9 mA 12 470 Ω 4 mW 49 mW <12NC> Application note © Koninklijke Philips Electronics N.V. 2005. All rights reserved. Rev. 01.00 — 20 June 2005 8 of 12 AN10361 Philips Semiconductors BISS loadswitch solutions 6. Calculating and selecting BISS loadswitches Typically, there are three application based parameters: Maximum input voltage, switch current and maximum voltage drop. Further, there might be a limitation for Tr2’s base current and for the maximum power dissipation of the loadswitch circuit (parameter definition refers to Fig 1). Selection criteria: • VCEO (Tr1) ≥ Vin determining breakdown voltage (Tr1) • IC (Tr1) ≥ I determining collector current (Tr1) • IB (Tr1) = IC (Tr1) / (IC/IB) (Tr1) setting base current (Tr1), IC/IB := 10 – 100 • R3 = (Vin - VBEsat (Tr1) - VCEsat (Tr2)) / IB calculating resulting resistance value (R3) • PR3 = IB² x R3 calculating resistor’s power dissipation (R3) • (IC/IB) (Tr2) = IB (Tr1) / IB (Tr2) IC/IB ≤ 100, transistor saturated? • R1 = (Vctrl - VBEsat (Tr2)) / IB (Tr2) calculating base resistor (R1) The data sheet contains all relevant information like limiting values and VCEsat curves. Example: Vin = 5 V; I = 200 mA; Vctrl = 3,3 V; Ictrl = 0,5 mA; Vdrop = 100 mV typical • VCEO (Tr1) := 15 V • IC (Tr1) := 0.5 A Î PBLS15xxV • IB (Tr1) = 200 mA / 20 = 10 mA Î IC/IB = 20 sufficient for Vdrop requirement • R3 = (5 V – 1 V – 0.5 V) / 10 mA = 350 Ω • PR3 = (10 mA)² x 330 Ω = 33 mW Î 330 Ω (next lower E24 value), size 0603 • (IC/IB) (Tr2) = 10 mA / 0.5 mA = 20 • R1 = (3.3 V – 0.8 V) / 0.5 mA = 5 kΩ Î PBLS1502V (R1 = 4.7 kΩ) This example is based on nominal values and yet disregards parameter spread of the resistance values and saturation voltage. Table 7: gives an overview about the released BISS loadswitch types (June 2005). Table 7: The BISS loadswitch portfolio contains 0,5 A and 1 A types IC Tr1 VCEO Tr1 0.5 A 1A [2] SOT457 (SC-74) SOT363 (SC-88) SOT666 VCEsat @ IC = 0,5 A 15 V PBLS15xxY PBLS15xxV 250 mV 40 V PBLS40xxY PBLS40xxV 350 mV 20 V PBLS20xxD 150 mV 40 V PBLS40xxD 170 mV 60 V PBLS60xxD 180 mV Note: “xx” indicates a sequential number used to distinguish between different internal resistance values R1 and R2: 01 – 2.2 kΩ, 02 – 4.7 kΩ, 03 – 10 kΩ, 04 – 22 kΩ <12NC> Application note © Koninklijke Philips Electronics N.V. 2005. All rights reserved. Rev. 01.00 — 20 June 2005 9 of 12 AN10361 Philips Semiconductors BISS loadswitch solutions 7. Applications for BISS loadswitches Beside standard applications like a supply line switch (e.g. camera module in a mobile phone) in Fig 10 or as high side switch (e.g. fan driver in a notebook) in Fig 11 the BISS loadswitches can be used to realize a voltage selector or a switchable constant current source. Fig 12 shows a voltage selector which switches either 3.3 V or 5 V to Vout depending on the logic signal at Vsel as it could be used to manage 3.3 V and 5 V SIM cards. The voltage drop of both input rails is minimized by applying a BISS loadswitch for the 5 V rail and a low VF (MEGA) Schottky rectifier2 or a low VF small signal Schottky diode for the 3.3 V rail. If other voltages are used, please note that always the higher voltage needs to be connected to the Schottky diode. A generic constant current source is given in Fig 13. R1 sets the current through D1 and D2, which must be much higher than the base current through Tr1 to achieve an unloaded voltage divider. R2 is used to set the output current Iout. The output current can be switched off by connecting Ven to ground. Relays or fan (1) Tr1, Tr2, Rint: 1x PBLS-series R1: 1x standard resistor (2) Tr1, Tr2, Rint: 1x PBLS-series R1: 1x standard resistor Fig 10. Supply line switch uses only two components Fig 11. Two component loadswitch Iout = 0.7 V / R4 (3) Tr1, Tr2, Rint: 1x PBLS-series D1: 1x PMEG-series or 1x BAT754 R1: 1x standard resistor Fig 12. Voltage selector needs only three instead of six single components 2. (4) Tr1, Tr2, Rint: 1x PBLS-series D1, D2: 1x BAV99W R1, R2: 2x standard resistors Fig 13. Switchable constant current source only requires four instead of eight single components see also AN10230: “The PMEG1020EA and PMEG2010EA MEGA Schottky diodes – a pair designed for high efficiency rectification” <12NC> Application note © Koninklijke Philips Electronics N.V. 2005. All rights reserved. Rev. 01.00 — 20 June 2005 10 of 12 AN10361 Philips Semiconductors BISS loadswitch solutions 8. Disclaimers Life support — These products are not designed for use in life support appliances, devices, or systems where malfunction of these products can reasonably be expected to result in personal injury. Philips Semiconductors customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify Philips Semiconductors for any damages resulting from such application. Right to make changes — Philips Semiconductors reserves the right to make changes in the products - including circuits, standard cells, and/or software - described or contained herein in order to improve design and/or performance. When the product is in full production (status ‘Production’), relevant changes will be communicated via a Customer Product/Process Change Notification (CPCN). Philips Semiconductors assumes no responsibility or liability for the use of any of these products, conveys no licence or title under any patent, copyright, or mask work right to these products, and makes no representations or warranties that these products are free from patent, copyright, or mask work right infringement, unless otherwise specified. Application information — Applications that are described herein for any of these products are for illustrative purposes only. Philips Semiconductors make no representation or warranty that such applications will be suitable for the specified use without further testing or modification. <12NC> Application note © Koninklijke Philips Electronics N.V. 2005. All rights reserved. Rev. 01.00 — 20 June 2005 11 of 12 AN10361 Philips Semiconductors BISS loadswitch solutions 9. Contents 1. Introduction .........................................................3 2. The loadswitch circuit.........................................3 3. Bipolar transistor products for loadswitch applications .........................................................4 4. The SOT666 BISS loadswitch demo board .......5 5. Measurement results ..........................................7 6. Calculating and selecting BISS loadswitches ..9 7. Applications for BISS loadswitches ................10 8. Disclaimers ........................................................11 9. Contents.............................................................12 © Koninklijke Philips Electronics N.V. 2005 All rights are reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. No liability will be accepted by the publisher for any consequence of its use. Publication thereof does not convey nor imply any license under patent- or other industrial or intellectual property rights. Date of release:20 June 2005 Document number: <12NC> Published in Germany