PT8A2704/04A
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Simple Fast Charger Controller
Product Features
Fast charge of nickel cadmium (NiCd) or nickel-
metal hydride (NiMH) batteries
Fast-charge termination by negative delta voltage,
maximum voltage, maximum temperature, and 90
minutes charging time
Support 1 to 8 cells fast charging
10% (PT8A2704) or 4% (PT8A2704A) of constant
charging current for trickle charging
On-chip 2.0V regulator
On chip precise ADC
Internal RC oscillator with external R&C
components
Low cost 8-pin DIP/SOIC package
Product Description
The PT8A2704/04A Fast-Charger IC is low-cost CMOS
battery-charge controller providing reliable charge
termination
for
both
NiCd
and
NiMH
battery
applications, such as Power tool and Consumer
electronics. A current-limited or constant–current supply
allows the PT8A2704/04A to be a cost-effective charger
with
only
a
few
external
components.
The
PT8A2704/04A has programmable charging time and
programmable trickle charging rate control by options in
a single IC for charging NiCd or NiMH battery cells.
For safety, fast or trickle charging is inhibited if the
battery temperature is over a safety threshold. Fast
charge is terminated by any of the following:
- Negative delta voltage/zero delta voltage
- Maximum voltage
- Maximum temperature
- Maximum time
Applications
Rechargeable shavers and hair cutters
Rechargeable RC cars
Rechargeable power tools
Pin Assignment and Pin Description
Pin Description
PT8A2704/04A
DIP-8 or SOIC-8
Package (Top View)
Pin
No.
1
2
3
4
5
6
7
8
Pin
Name
GND
VB
VT
OSC
CORD
VCC
CHARGE
VEE
I/O
-
I
I
I
I
-
O
O
Description
Power ground
Battery voltage input (1.6V – 1.8V)
NTC voltage input(1.6V – 1.8V)
RC oscillator input, external resistor
pull-up and capacitor pull-down
Cord detection input
Positive power supply voltage
Charging control enable
2.0v regulated voltage
12-07-0005
1
PT0199-8
07/05/12
PT8A2704/04A
Simple Fast Charger Controller
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Block Diagram
Functional Description
Voltage Regulator (2.0V Regulator):
Build-in voltage regulator used to power supply RC oscillator, precise ADC.
Oscillator:
Internal RC oscillator to generate a 64 kHz clock for internal system.
POR (Power-on Reset):
Power on reset to reset all internal logic while power on.
Charging Control:
Charging control enables output CHARGE pin which can be used to show charging status. It is logic high
during constant current charging and 12.5Hz with 10% (for PT8A2704) or 4% (for PT8A2704A) duty cycle during trickle current
charging
AC Cord Control:
CORD input is external cord detection pin (digital level), active high.
Precision ADC:
VB
measures the battery voltage. VB is a divide voltage from the battery voltage. When VB exceeds the maximum voltage
(0.9VEE), fast charging will be terminated. Moreover, VB detects the negative delta voltage during fast charging. It is suggested
to set the termination voltage of VB within the input range of the ADC which is 0.8VEE to 0.9VEE.
VT
measures the temperature of the battery with an external NTC (refer to
How to determine RX1 on page5).
Maximum
temperature termination occurs when the VT exceeds a temperature cut-off threshold voltage (eg. 50˚C which equivalent to
0.887VEE). Constant current or trickle charging will stop completely when the temperature exceeds another threshold voltage (eg.
55˚C which equivalent to 0.897VEE).
Charging Cycle Phases
No charging
Fast charging
Pulse-trickle
Stop charging
CORD
CHARGE
Fast charge is started when the CORD is high. If the battery voltage is over the limit or temperature exceeds 50˚C, pulse-trickle
charge begins and the device charges the battery with trickle charge till the CORD is low (see above Figure).
Fast charge will be termination by one or more of the four possible termination conditions:
negative delta voltage/delta voltage
maximum voltage
maximum temperature
maximum time
12-07-0005
2
PT0199-8
07/05/12
PT8A2704/04A
Simple Fast Charger Controller
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Maximum Ratings
Storage Temperature…………………………………………... -25oC to +85oC
Supply Voltage to Ground Potential (V
CC
)…………. ……………...…-0.5V to 6V
DC Input Voltage…………………… ……………..……… -0.5V to V
CC
+0.5V
DC Output Current……………………………………………....20mA
Power Dissipation…………………………………………...…500mW
Note:
Stresses greater than those listed under MAXIMUM
RATINGS may cause permanent damage to the
device. This is a stress rating only and functional
operation of the device at these or any other condi-
tions above those indicated in the operational sec-
tions of this specification is not implied. Exposure
to absolute maximum rating conditions for extended
periods may affect reliability.
Recommended Operation Condition
Parameters
V
CC
ADC V
IN
Fosc
T
A
Description
Operating Voltage
Input voltage range (VT, VB)
Frequency of oscillator (C=390pF, R=47kΩohm)
Operation Temperature
Min.
2.2
0.8
54.4
0
Type.
2.4
-
64
25
Max.
5.5
0.9
73.6
70
Unit
V
VEE
kHz
˚C
DC Electrical Characteristics
(T
A
= 0~70° V
CC
= 2.4V unless otherwise claims)
C,
Symbol Description
Input Low/HIGH leakage current for
I
IL
, I
IH
CORD pin
I
OH
Output HIGH current
I
OL
Output LOW current
VEE Regulator output voltage
Line Regulation of regulator
V
O
Load regulation
Maximum battery voltage to stop fast-
VBmax
charge
Maximum VT voltage for battery
VTmax temperature detection to stop fast-
charge
Rslt
Average A/D resolution of ADC
DNL ADC Differential nonlinearity
INL
ADC Integral nonlinearity
I
CC
Supply Current
V
LDR
Test Conditions
V
CC
=2.4V,V
IL
=0.2V, V
IH
=2.2V
CHARGE pin, V
OH
=2.2V
CHARGE pin, V
OL
=0.2V
No load
2.2VV
CC
3.0V,
No load
0mA
I
L
3mA
-
-
No load
No load
No load
R=47kΩ, C=390pF, no load
Min.
-1
-3
3
1.9
-
-
-
-
6.00
-
-
-
Typ.
-
-
-
2.0
-
-
0.9
0.897
6.25
1
1
-
Max.
1
-
1
2.1
50
50
-
-
6.50
-
-
380
Unit
μA
mA
V
mV
mV
VEE
VEE
mV
LSB
LSB
μA
AC Electrical Characteristics
(T
A
= 0~70° V
CC
= 2.2V~3.0V)
C,
Symbol Description
F
OSC
Oscillator Frequency
T
FC
Maximum fast-charge time
DC
Test Conditions
C=390pF, R=47kΩ
OSC=64kHz
Duty-cycle of charge pin output in PT8A2704
trickle charge mode
PT8A2704A
Min.
54.4
-
7
3
Typ.
64
90
10
4
Max.
73.6
-
13
5
Unit
kHz
Minutes
%
%
12-07-0005
3
PT0199-8
07/05/12
PT8A2704/04A
Simple Fast Charger Controller
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Typical Application Circuit
1. Application circuit for larger discharging current.
PT8A2704/04A Application Circuit for Shaver with Two Batteries
Note:
a. R1 value can be adjusted to make sure the CORD voltage is around 2.0V.
b. As the device is always powered by battery, the static consumption must be considered in application design.
12-07-0005
4
PT0199-8
07/05/12
PT8A2704/04A
Simple Fast Charger Controller
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2. Application circuit for smaller discharging current.
If discharging current is smaller, suggest using the following schematic:
PT8A2704/04A Application Circuit for Shaver with Two Batteries
PCB Layout Constraint
1. Cross angle between two Tracks should be larger than 90 degree.
2. Track should be short and wide enough to reduce voltage drop, especially Power supply and Ground as well as some tracks
flowing with large current, such as switch Q1.
3. A ceramic cap C6 about 103 need to add between VT and Ground of PT8A2704 in order to prevent detection circuit from noise.
4. A ceramic cap C7 about 103 and C8 10μF Tan cap need to add between VB to Ground.
How to determine RX1
Assuming Resistance of NTC at 55˚C is RT.
See right figure, below formula can be attained.
VT=RX1*VEE/ (RX1+RT) =1.8V
VEE=2.0V, finally
RX1=9*RT
VEE
NTC
VT
RX1
12-07-0005
5
PT0199-8
07/05/12
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