Application Note 32 Issue 1 January 2000 Features and Applications of the ZDS1009 Current Mirror/Level Translator Neil Chadderton Introduction The ZDS1009 current mirror has been developed specifically for high side, current sense plus level translation applications and as such will find a broad applications base including battery charge management, DC motor control and over current monitoring functions. It is of particular interest for current sense applications for feedback purposes in fast battery chargers for Li-Ion cell based systems. The device f unctions by sensing t he voltage developed across an external (user d ef i ne d) h ig h s id e c ur r e nt s ens e resistor, and by an arrangement of current mirrors refers this sensed voltage, with or without multiplication, to a low side referenced signal. This signal can then be used to close the control loop to the controller IC, for the DC-DC converter providing the charge to the battery. Features and Benefits High side Current Sense and Referencing to Low Side Signal Multiplication Excellent Temperature Tracking Characteristic C o m p a c t , C o st E f f ec t iv e Solution Only Four Connections Required Low Component Count Simplifies Circuit Implementation Broad Application Base from Single cell Li-Ion chargers to Multi-cell Lead-Acid systems DC Motor Control Over Current Monitors Typical End Products Battery c hargers, particularly AN 32 - 1 Li-Ion based systems, for either stand alone units or support units for portable systems including: Cellphones, GPS systems, POS t e r m i n a l s , m e d i c a l monitors, dataloggers, test equipment and instrumentation DC motor controller systems Over current monitors Battery conditioning and monitoring systems Applications Note 32 Issue1 January 2000 Description The part is supplied in an eight lead package, the SM8, (see Appendix B) and requires only four connections into the circuit and four external resistors to effect a complete, accurate and cost effec tive current sense plus level t ranslation circuit. The maximum operating ratings of the part are 30V and 1A, though in practice the operating current is likely to be of the order of a few mA at most. The part is connected into the circuit using the E1, E2, E3 and E4 pins, corresponding to the Emitter nodes on the functional diagram shown in Figure 1. The other pins of the ZDS1009 are normally unused, though some applications may use the X2 or Y2 nodes (see Applications considerations later). For most applications all pins other than the E1-4 pins are left open circuit. Figure 1 Functional Diagram Figure 2 Typical Application Circuit. The device operates by current mirror action. The voltage developed across the current sense resistor (R2 in Figure 2) for example, by the charging current in a battery charging system,is also developed across R1 due to the inherent matching of the PNPs (defining the same IC for a given VBE ). As the current flowing through R1 also flows through R4 (less the base current of E3 and E1) then if R4 equals R1, R4 will also develop the same voltage across it as R2, but referenced to the low side of R3 and R4. Therefore the high side sensed voltage (representing the current) has been referred to the low side. By adjustment of the R1 and R4 ratio, multiplication factors can be introduced into the loop, to provide the scaled value as required for a controller IC for example. AN 32 - 2 Applications Note 32 Issue1 January 2000 Typical Application Circuit The part is used as shown in the typical application circuit of Figure 2. For example, with R2=200m a n d R1=R3=R4=100, t his circuit would provide a current to voltage sensitivity of 200mV/A. The components used with the ZDS1009 are detailed below: 1. R2 is an high side current sense resistor through which the current to be sensed is passed. In the case of a fast battery charger, R2 would be placed after the switching regulator that provides the constant current/voltage as required by the battery chemistry being employed. For other applications, the power supply input would be applied to the junction of R1 and R2. The junction of R2 and E2 being connected to the load/battery. 2. The scaling resistors R1 and R4 are used to set the multiplication factor required, to provide the full scale input voltage as defined by the charge current I, R2 and the sensitivity of the controller’s feedback pin. The transfer equation is: Vsense=I x R2 x R4/R1 (R4=R3) 3. R3 is used for balancing purposes, to ensure that the current passing through each limb of the device is equal, thereby reducing the offset voltage at the output pin. The offset voltage produced by the part potentially introduces inaccuracies into the control loop, so an appreciation of the likely magnitude of the offset voltage is important to gauge the effects on a particular circuit. The chart shown in Figure 3 shows the offset voltage Figure 3 Offset Voltage Obtained at the Output Pin (E4) with Zero Current Flowing Through R1. obtained at the output pin (E4) with zero current flowing through R2. This is for a circuit configured similarly to that of Figure 2, but with R2 having a value of 330m, p r ov iding a sensit ivity of 330mV/A. R1, R3 and R4 are again equal to 100. This shows that 71% of parts have an offset less than 300V, and 89% have an offset less than 1.48mV. Internal process changes have reduced the percentage of parts with higher offset values such that the internal test limit used at Production Test is now set to guarantee a 4mV maximum for this parameter. 4. A suggested layout for an evaluation PCB with suggested components is given in Appendix A. AN 32 - 3 Applications Note 32 Issue1 January 2000 Figure 4 The ZDS1009 Supporting the Benchmarq bq2954 Charge Management IC. Li-Ion Charger Circuit Figure 4 shows the ZDS1009 supporting the Benchmarq bq2954 Charge Management IC. Most of the support components for the bq2954 are omitted for clarity. This design also uses the Zetex FZT789A high current Super- PNP as the switching transistor in the DC-DC step down converter and the FMMT451 as the drive NPN for the FZT789A. The evaluation circuit as presented in reference 2 Appendix C, can be configured to charge up to four Li-Ion cells at a charge current of 1.25A. Charge can be terminated on maximum voltage, selectable minimum current, or maximum time out. Switching frequency of the PWM loop is approximately 120kHz. Complete details of the bq2954 and its supporting evaluation board can be found via the references given in Appendix C. Application Considerations 1. It is desirable to minimize the current through the two limbs of the mirror to prevent internal temperature differentials and to maintain the desired output current - the output current can be reduced by the ZDS1009 (outer) limb current depending on resistor values, and so this may introduce a slight error. This can be corrected if desired with an additional offset. 2. Observe the minimum operation voltage, (termed Output cut-off voltage on the datasheet). This should not be problem in the majority of circuits as this minimum is lower than common single cell voltages. AN 32 - 4 Applications Note 32 Issue1 January 2000 4. For operation at very low t emperat ures ( <-20° C) , it may be necessary to include an additional resistor connected between Y2 and ground. See Figure 6. This is to kick-start the normal self feeding (initiated by transistor leakage current) current mirror action - at low temperatures, the transistor leakage may be reduced below the value where the current mirrors can self-start. Figure 5 Minimising Quiescent Current. 3. In some battery life critical applications, the quiescent current of the ZDS1009 (~50A for the circuit shown in Figure 2 and when the charger is not operating) may be considered an undesirable current drain on the system battery. In these circumstances, an N Channel MOSFET may be used to disconnect the low side terminals of the mirror, when the current sense function is not required. See Figure 5. Figure 6 Operation at Low Temperature. AN 32 - 5 APPENDIX A Applications Note 32 Issue1 January 2000 Suggested Evaluation PCB. A suggested PCB layout to permit evaluation of the ZDS1009 is shown in Figure 8 (derived from the schematic of Figure 7). Of course it is likely that this subcircuit would likely be reproduced as part of the intended system, but is included here for interest. Figure 8 S uggested PC B Layout to Allow Evaluation of the ZDS1009 Current Mirror and Level Translator. Figure 7 Typical Application Circuit for the ZDS1009. Designation Quantity Description Package Source U1 1 ZDS1009 Current Mirror + Level Translator SM8 Zetex R2 1 LR2010-01-R200-F 2010 IRC R1,R3,R4 3 PCF-W1206R-03-1000-B 1206 IRC 200m , 1% Component Suppliers Resistors IRC, Corpus Christi, TX 78411 Tel: (361)-992-7900 FAX: (361)-992-3377 http://www.irctt.com AN 32 - 6 100, 0.1% APPENDIX B Applications Note 32 Issue1 January 2000 ZDS1009 SM-8 COMPLEMENTARY CURRENT MIRROR DESCRIPTION The ZDS1009 current mirror has been developed specifically for high side, current sense plus level translation applications and as such will find a broad applications base including battery charge management, DC motor control and over current monitoring functions. It is of particular interest for current sense applications for feedback purposes in fast battery chargers for Li-Ion cell based systems. The device functions by sensing the voltage developed across an external (user defined) high side current sense resistor, and by an arrangement of current mirrors refer this sensed voltage, with or without multiplication, to a low side referenced signal. This signal can then be used, for example, to close the control loop to a controller IC, for a DC-DC converter providing charge to a battery. FEATURES • Excellent Temperature Tracking Characteristics • Compact Cost Effective Solution • Simplifies Circuit Implementation • Broad application base from Single Cell Li-ion High Side Current sense chargers to Multi-cell Lead-Acid systems • Only 4 Connections required SCHEMATIC DIAGRAM SM-8 (8 LEAD SOT223) TYPICAL APPLICATION CIRCUIT Vsense = IR2 R 4 R1 For balance R3=R4 eg R2=100mΩ R1=R3=R4=100Ω Vsense sensitivity = 100mV/A CONNECTION DIAGRAM ISSUE 2 - JANUARY 2000 1 AN 32 - 7 APPENDIX B Applications Note 32 Issue1 January 2000 ZDS1009 ABSOLUTE MAXIMUM RATINGS. PARAMETER SYMBOL VALUE UNIT Maximum Operating Voltage V y1-x1 120 V Maximum Voltage (E1-E2,E3-E4) V E-E’ 10 V Peak Pulse Current IM 4 A Continuous Current (E1-E4,E2-E3) IC 1 A Total Power Dissipation at T amb = 25°C* P tot 2 W Operating and Storage Temperature Range T j :T stg -55 to +150 °C * The power which can be dissipated assuming the device is mounted in a typical manner on a PCB with copper equal to 2 inches square. ELECTRICAL CHARACTERISTICS (at Tamb=25°C) Parameter Symbol Min Breakdown Voltage BV Y1-X1 120 Max Breakdown Voltage BV X1-E1 -30 V I X1 =-10mA Breakdown Voltage BV Y1-E3 30 V I Y1 =10mA Breakdown Voltage BV E1-Y1 -12 V I E1 =-100µA Breakdown Voltage BV E2-Y1 -6 V I E2 =-100µA Breakdown Voltage BV E3-X1 12 V I E3 =100µA Breakdown Voltage BV E4-X1 6 V I E4 =100uA Leakage I Y1 50 nA V Y1-X1 =100V Leakage I X1 -10 µA V X1-E1 =-30V, V y1 =V E1 Leakage I Y1 10 µA V Y1-E3 =30V,V X1 =V E3 Leakage I E1 -100 nA V E1-Y1 =-8V Leakage I E2 -100 nA V E2-Y1 =-4V Leakage I E3 100 nA V E3-X1 =8V Leakage I E4 100 nA V E4-X1 =4V Input Voltage V Y1-E2 -1.45 -1.65 V I Y1 =-1A Input Voltage V Y1-E3 1.45 1.75 V I Y1 =1A,V X1 =V Y1 Input Voltage V X1-E1 -1.45 -1.75 V I X1 =-1A,V X1 =V Y1 Input Voltage V X1-E4 1.45 1.65 V I X1 =1A Transfer Characteristic V OUT 0.99 1.01 V See Fig 1.V CC =5V R1=R3=R4=100Ω, V IN =1V Transfer Characteristic V OUT 1 mV See Fig 1.V CC =5V R1=R3=R4=100Ω, V IN =5mV Output Zero-Offset Voltage V OFFSET mV See Fig 2.V CC =5V,R 2 <1Ω R1=R3=R4=100Ω 4 Unit Conditions V I Y1 =100µA ISSUE 2 - JANUARY 2000 2 AN 32 - 8 APPENDIX B Applications Note 32 Issue1 January 2000 ZDS1009 TYPICAL CHARACTERISTICS 1.20 1.3 +25°C Vin = 0.1V Vcc=5V 1.10 1.05 R = 10⍀ R = 100⍀ R = 1 k⍀ 1.00 1.1 Voltage Transfer Voltage Transfer +25°C 1.2 1.15 1.0 0.8 0.95 0 5 10 15 20 25 30 R = 10⍀ R = 100⍀ R = 1 k⍀ 0.9 0.7 10m 35 100m Vcc - Supply Voltage(V) Voltage Transfer v Supply Voltage Phase Change (Degrees) Voltage Transfer 0.90 R = 10k⍀ R = 1k⍀ R = 100⍀ 0.70 Vin = 1V Vcc = 5V 0.60 10 Voltage Transfer v Input Voltage 1.00 0.80 1 Vin - Input Voltage (V) VAC = 0.1V 180 200 220 R = 10k⍀ 240 R = 1k⍀ R = 100⍀ 260 280 Vin = 1V 300 Vcc = 5V VAC = 0.1V 320 340 T = 25°C T = 25°C 0.50 100 1k 10k 100k 360 1k 1M Frequency (Hz) 10k 100k 1M Frequency (Hz) Phase Change v Frequency Response Voltage Transfer v Frequency Response TEST CIRCUITS Figure 2 Output Zero-Offset Voltage Test Circuit Figure 1 Transfer Characteristic Test Circuit ISSUE 2 - JANUARY 2000 3 AN 32 - 9 APPENDIX B Applications Note 32 Issue1 January 2000 ZDS1009 TYPICAL CHARACTERISTICS NPN 1.4 PNP 1.4 +25°C +25°C Iout = 0.95Iin Iout = 0.95Iin 1.2 Voltage - (V) Voltage - (V) 1.2 1.0 0.8 Vin Vcutoff 0.6 0.4 100µA 1mA 10mA 100mA 1.0 0.8 Vin Vcutoff 0.6 0.4 100µ 1A 1m Iin - Input Current (A) 10m NPN Iin = 1mA Iout = 0.95mA 1.4 1.2 1.2 1.0 0.8 0.6 Vcutoff 0.4 1.0 Voltage (V) Voltage (V) PNP 1.6 Iin = 1mA Iout = 0.95mA 1.4 0.8 0.6 0.4 Vcutoff 0.2 Vin Vin 0.2 0 -55 -35 -15 5 25 45 65 85 105 0 -60 125 -40 Temperature (°C) 0 20 40 60 80 100 120 Input/Output Voltage v Temperature PNP NPN 1.05 1.05 +25°C 25 C 1.04 1.03 1.03 1.02 1.02 Current Transfer Current Transfer -20 Temperature (°C) Input/Output Voltage v Temperature 1.04 1A Input/Cutoff Voltage v Iin Input/Cutoff Voltage v Iin 1.6 100mA Iin - Input Current (A) 1.01 1.00 0.99 10mA 1mA 100µA 0.98 0.97 0.96 0.95 1.01 1.00 0.99 0.98 10mA 0.97 1mA 100µA 0.96 0.95 1m 1 10 0.1 100 Vce (V) - Collector-Emitter Voltage (V) 1 10 Vce - Collector-Emitter Voltage(V) Current Transfer v Vce Current Transfer v Vce ISSUE 2 - JANUARY 2000 4 AN 32 - 10 APPENDIX B Applications Note 32 Issue1 January 2000 ZDS1009 PACKAGE DIMENSIONS He A E DIM A1 Millimetres Inches Typ Max Min Typ Max A - - 1.7 - - 0.067 A1 0.02 - 0.1 0.0008 - 0.004 b - 0.7 - - 0.028 - c 0.24 - 0.32 0.009 - 0.013 D 6.3 - 6.7 0.248 - 0.264 E 3.3 - 3.7 0.130 - 0.145 e1 - 4.59 - - 0.180 - e2 - 1.53 - - 0.060 - He 6.7 - 7.3 0.264 - 0.287 Lp 0.9 - - 0.035 - - α - - 15° - - 15° β - 10° - - 10° - e1 e2 3 6 4 5 Min 8 1 2 7 o 45° c Lp ORDERING INFORMATION DEVICE PARTMARKING ZDS1009 S1009 ISSUE 2 - JANUARY 2000 5 AN 32 - 11 APPENDIX C Applications Note 32 Issue1 January 2000 REFERENCES 1. Unitrode/Benchmarq bq2954 d a t a s h e e t - “ L i t h i u m I o n C h ar g e Management IC with Integrated Switching Controller” 2. Unitrode/Benchmarq bq2954 demonstration PCB support literature “DV2954S1H: Li-Ion Charger Development System - Control of On-board PNP Switch Mode Regulator with High Side Current Sensing”. Zetex plc. Fields New Road, Chadderton, Oldham, OL9-8NP, United Kingdom. Telephone: (44)161 622 4422 (Sales), (44)161 622 4444 (General Enquiries) Fax: (44)161 622 4420 Zetex GmbH Streitfeldstraße 19 D-81673 München Germany Telefon: (49) 89 45 49 49 0 Fax: (49) 89 45 49 49 49 Zetex Inc. 47 Mall Drive, Unit 4 Commack NY 11725 USA Telephone: (631) 543-7100 Fax: (631) 864-7630 Zetex (Asia) Ltd. 3510 Metroplaza, Tower 2 Hing Fong Road, Kwai Fong, Hong Kong Telephone:(852) 26100 611 Fax: (852) 24250 494 These are supported by agents and distributors in major countries world-wide Zetex plc 2000 Internet:http://www.zetex.com This publication is issued to provide outline information only which (unless agreed by the Company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. The Company reserves the right to alter without notice the specification, design, price or conditions of supply of any product or service. AN 32 - 12