LTC4123
Low Power
Wireless Charger for Hearing Aids
FeaTures
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DescripTion
The
LTC
®
4123
is a low power wireless receiver and a
constant-current/constant-voltage linear charger for NiMH
batteries. An external programming resistor sets the charge
current up to 25mA. The temperature compensated charge
voltage feature protects the NiMH battery and prevents
overcharging.
Wireless charging with the LTC4123 allows products to
be charged while sealed within enclosures and eliminates
bulky connectors in space constrained environments. The
LTC4123 also makes it possible to charge NiMH batteries
used in moving or rotating equipment.
The LTC4123 prevents charging of Zinc-Air batteries as well
as batteries inserted with reverse polarity. The LTC4123
pauses charging if its temperature is too hot or too cold.
An internal timer provides time-based charging termination.
The 2mm
×
2mm DFN package and low external compo-
nent count make the LTC4123 well-suited for hearing aid
applications or other low power portable devices where
small solution size is mandatory.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Complete Low Power Wireless NiMH Charger
Low Minimum Input Voltage: 2.2V
Small Total Solution Volume
1.5V, 25mA Linear Single-Cell NiMH Charger
Temperature Compensated Charge Voltage
Integrated Rectifier with Overvoltage Limit
Zinc-Air Battery Detection
Reverse Polarity Protection
Thermally Enhanced 6-Lead (2mm
×
2mm)
DFN package
applicaTions
n
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n
Hearing Aids
Smart Cards
Fitness Devices
Moving and/or Rotating Equipment
Typical applicaTion
25mA NiMH Wireless Battery Charger
AIR GAP
T
x
COIL
TRANSMITTER
CIRCUIT
L
RX
13µH
LED
C
RX
33nF
CHRG
C
IN
4.7µF
GND PROG
R
PROG
953
4123 TA01
Complete Wireless Charging Solution for a Hearing Aid
ACIN
BAT
V
CC
LTC4123
I
CHARGE
=
25mA MAX
V
IN
+
–
+
1.5V
NiMH
BATTERY
For more information
www.linear.com/LTC4123
1
4123f
LTC4123
absoluTe MaxiMuM raTings
(Notes 1, 3)
pin conFiguraTion
TOP VIEW
ACIN 1
V
CC
2
CHRG
3
7
GND
6 GND
5 BAT
4 PROG
Input Supply Voltages
V
CC
........................................................ –0.3V to 5.5V
ACIN .................................................. –10V to V
CC
+1V
Input Supply Currents
I(ACIN) ............................................................ 200mA
BAT ................................................................. –2V to 2V
PROG,
CHRG.....................................
–0.3V to V
CC
+0.3V
Operating Junction Temperature Range
(Note 2)........................................................ –20 to 85°C
Storage Temperature Range ......................–65 to 150°C
DC PACKAGE
6-LEAD (2mm
×
2mm) PLASTIC DFN
T
JMAX
= 85°C,
θ
JA
= 80.6°C/W
EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LTC4123EDC#PBF
TAPE AND REEL
LTC4123EDC#TRPBF
PART MARKING*
LGSY
PACKAGE DESCRIPTION
6-Lead (2mm
×
2mm) Plastic DFN
TEMPERATURE RANGE
–20°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
ACIN
= 0V, V
CC
= 5V unless otherwise noted (Notes 2, 3, 4).
SYMBOL
V
CC
I
VCC
V
UVLO
V
BAT
PARAMETER
Input Supply Operating Range
Input Quiescent Operating Current
Hysteresis
Battery Charge Voltage
T
A
= 25°C
T
A
= –10°C (Note 4)
T
A
= 75°C (Note 4)
I
BAT(LEAK)
V
PROG
h
PROG
I
CHG
V
UVCL
T
CHG
Battery Pin Discharge Current
PROG Pin Servo Voltage
Ratio of BAT Current to PROG Current
Constant-Current Mode Charge Current
Undervoltage Current Limit
Charge Termination Period
R
PROG
= 23.7kΩ
R
PROG
= 953Ω
R
PROG
= 4.99kΩ
4.8
l
l
elecTrical characTerisTics
CONDITIONS
l
MIN
2.2
l
TYP
125
MAX
5
200
2.02
1.5195
1.610
1.3975
100
UNITS
V
µA
V
mV
V
V
V
nA
V
mA/mA
Charging Terminated. I
BAT
and I
PROG
= 0A
Input Supply Undervoltage Lockout Threshold V
CC
Rising
1.88
1.4955
1.580
1.3675
1.95
40
1.5075
1.595
1.3825
0.25
96
Charger Terminated or V
CC
< V
UVLO
, V
BAT
= 2V
0.73
22
1
25
2.2
6
1.27
28
7.2
mA
mA
V
Hours
2
4123f
For more information
www.linear.com/LTC4123
LTC4123
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
ACIN
= 0V, V
CC
= 5V unless otherwise noted (Notes 2, 3, 4).
SYMBOL
PARAMETER
Cold Temperature Fault Threshold
Hysteresis
Hot Temperature Fault Threshold
Hysteresis
Zinc-Air Battery Detection
V
Zn-AIR
T
Zn-AIR
Zinc-Air Fault Threshold Voltage
Hysteresis
Zinc-Air Detection Period
Charge Voltage Limit
Zinc-Air Detection Charge Current
Reverse Polarity Detection
V
REVPOL
Reverse Polarity Threshold Voltage
Hysteresis
AC Rectification
V
CC(HIGH)
V
CC(LOW)
V
CC
High Voltage Limit
V
CC
Low Voltage Limit
ACIN to V
CC
Voltage Drop
Status Pin (CHRG)
I
CHRG
CHRG
Pin Pull-Down Current
CHRG
Leakage Current
V
CHRG
= 450mV
CHRG
= 5V
250
340
430
1
µA
µA
V
CC
Rising
V
CC
Falling
I
VCC
= –20mA, Charger Terminated
5
3
0.65
V
V
V
V
BAT
Falling
–50
40
mV
mV
During Zinc-Air Battery Detection
R
PROG
= 23.7kΩ
V
BAT
Rising
1.60
1.65
40
80
1.8
1
V
mV
s
V
mA
Die Temperature Rising
CONDITIONS
Die Temperature Falling
MIN
TYP
–5
5
70
5
MAX
UNITS
°C
°C
°C
°C
Thermal Sensing
elecTrical characTerisTics
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC4123 is tested under conditions such that T
J
≈ T
A
. The
LTC4123E is guaranteed to meet specifications from 0°C to 85°C junction
temperature. Specifications over the –20°C to 85°C operating junction
temperature are assured by design, characterization and correlation with
statistical process controls. Note that the maximum ambient temperature
consistent with these specifications is determined by specific operating
conditions in conjunction with board layout, the rated package thermal
impedance and other environmental factors. The junction temperature
(T
J
, in °C) is calculated from the ambient temperature (T
A
, in °C) and
power dissipation (PD, in Watts) according to the following formula:
T
J
= T
A
+ (P
D
•
θ
JA
), where
θ
JA
(in °C/W) is the package thermal
impedance.
Note 3:
All currents into pins are positive; all voltages are referenced to
GND unless otherwise noted.
Note 4:
These parameters are guaranteed by design and are not 100%
tested. The battery charge voltage variation over temperature is guaranteed
in a ±15mV band as shown in the Typical Performance Characteristics curve.
For more information
www.linear.com/LTC4123
3
4123f
LTC4123
Typical perForMance characTerisTics
Battery Charge Current
vs Battery Charge Voltage
12.0
10.0
8.0
I
CHG
(mA)
V
BAT
(V)
6.0
4.0
2.0
R
PROG
= 2.49kΩ
0
1.30
1.35
1.40
1.45 1.50
V
BAT
(V)
1.55
1.60
4123 G01
T
A
= 25°C, unless otherwise noted.
Battery Charge Voltage
vs Supply Voltage
1.520
Battery Charge Voltage
vs Temperature
1.600
1.580
1.560
1.540
1.520
1.500
1.480
1.460
1.440
1.420
1.400
1.380
–5
R
PROG
= 23.7kΩ
10
25
40
TEMPERATURE (°C)
55
70
4123 G02
CHARGE VOLTAGE
CHARGE VOLTAGE MAX
CHARGE VOLTAGE MIN
1.515
V
BAT
(V)
1.510
1.505
1.500
R
PROG
= 23.7kΩ
3
3.5
4
4.5
SUPPLY VOLTAGE (V)
5
4123 G03
1.495
2.5
PROG Pin Voltage vs Temperature
(Constant Current Mode)
260
12.0
10.0
255
8.0
V
PROG
(mV)
250
I
CHG
(mA)
6.0
4.0
245
2.0
240
R
PROG
= 23.7k
–5
10
25
40
TEMPERATURE (°C)
55
70
4123 G04
Undervoltage Current Limit:
Charge Current vs Supply Voltage
1.00
R
PROG
= 2.49kΩ
0.80
Charge Current
vs PROG Pin Voltage
I
CHG
(mA)
0.60
0.40
0.20
R
PROG
= 23.7kΩ
0
2
2.2
2.4
2.6
2.8
SUPPLY VOLTAGE (V)
3.0
4123 G05
0
0
50
100
150
V
PROG
(mV)
200
250
4123 G06
Input Quiescent Current
vs Supply Voltage
150
V
BAT
= –100mV
140
I
BAT(LEAK)
(nA)
100
80
60
Battery Leakage Current
vs Temperature
2.00
1.98
SUPPLY VOLTAGE (V)
1.96
1.94
1.92
1.90
1.88
10
25
40
55
TEMPERATURE (°C)
70
85
4123 G08
UVLO Threshold vs Temperature
(Rising and Falling)
40
I
VCC
(µA)
130
20
0
–20
–40
110
–60
–80
100
2
2.5
3
3.5
4
SUPPLY VOLTAGE (V)
4.5
5
4123 G07
120
–100
–20
V
CC
= 0V
V
BAT
= 2V
–5
1.86
–20
UVLO FALLING
UVLO RISING
–5
10
25
40
55
TEMPERATURE (°C)
70
85
4123 G09
4
4123f
For more information
www.linear.com/LTC4123
LTC4123
Typical perForMance characTerisTics
V
CC
High and Low Thresholds
vs Temperature
5.00
380
T
A
= 25°C, unless otherwise noted.
CHRG
Pull-Down Current
vs Temperature
4.50
SUPPLY VOLTAGE (V)
360
I
CHRG
(µA)
V
CC(HIGH)
V
CC(LOW)
–5
10
25
40
55
TEMPERATURE (°C)
70
85
4123 G10
4.00
340
3.50
320
3.00
300
2.50
–20
280
–20
–5
10
25
40
55
TEMPERATURE (°C)
70
85
4123 G11
Charge Termination Period
vs Temperature
7.20
CHARGE TIMER ACCURACY (%)
20.0
15.0
10.0
5.0
0
–5.0
–10.0
–15.0
Charge Timer Accuracy
vs Supply Voltage
6.60
T
CHG
(Hours)
6.00
5.40
4.80
–5
10
25
40
TEMPERATURE (°C)
55
70
4123 G12
–20.0
2.2
2.9
3.6
4.3
SUPPLY VOLTAGE (V)
5.0
4123 G13
Maximum Available Wireless
Power vs Coil Spacing
125
MAXIMUM AVAILABLE POWER (mW)
MAX POWER
MAX CHARGE CURRENT
30
260
MAXIMUM CHARGE CURRENT AVAILABLE (mA)
Typical Wireless Charging Cycle
1.6
V
BAT
195
V
PROG
(mV)
1.2
V
BAT
(V)
100
24
75
18
130
See Figure 4
P675 NiMH
R
PROG
=976
f
DRIVE
=244kHz
L
TX
=760308103206
L
RX
=760308101208
0
1
2
3
0.8
50 R
PROG(MIN)
= 953Ω
L
RX
= 760308101208
25 L
TX
= 760308103206
f
DRIVE
= 244kHz
See Figure 4
0
1.5
3.5
5.5
7.5
9.5
COIL SPACING (mm)
12
6
65
V
PROG
0.4
0
11.5
4123 G14
0
4
5
6
4123 G15
0.0
TIME (HOURS)
For more information
www.linear.com/LTC4123
5
4123f
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