AN32

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
Similar pages