UC2909
UC3909
DESCRIPTION
The UC3909 family of Switchmode Lead-Acid Battery Chargers accurately
controls lead acid battery charging with a highly efficient average current
mode control loop. This chip combines charge state logic with average current PWM control circuitry. Charge state logic commands current or voltage
control depending on the charge state. The chip includes undervoltage
lockout circuitry to insure sufficient supply voltage is present before output
switching starts. Additional circuit blocks include a differential current sense
amplifier, a 1.5% voltage reference, a –3.9mV/°C thermistor linearization
circuit, voltage and current error amplifiers, a PWM oscillator, a PWM comparator, a PWM latch, charge state decode bits, and a 100mA open collector output driver.
Switchmode Lead-Acid Battery Charger
FEATURES
• Accurate and Efficient Control of
Battery Charging
• Average Current Mode Control from
Trickle to Overcharge
• Resistor Programmable Charge
Currents
• Thermistor Interface Tracks Battery
Requirements Over Temperature
• Output Status Bits Report on Four
Internal Charge States
• Undervoltage Lockout Monitors VCC
and VREF
1/99
BLOCK DIAGRAM
UDG-95007-1
Pin numbers refer to J, N, DW packages.
2
UC2909
UC3909
DIL-20, (Top View)
J or N, DW Packages
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC), OUT, STAT0, STAT1 . . . . . . . . . . . 40V
Output Current Sink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.1A
CS+, CS-. . . . . . . . . . . . . . . . . . . . . . . . . . -0.4 to VCC (Note 1)
Remaining Pin Voltages. . . . . . . . . . . . . . . . . . . . . . -0.3V to 9V
Storage Temperature . . . . . . . . . . . . . . . . . . . -65°C to +150°C
Junction Temperature . . . . . . . . . . . . . . . . . . . -55°C to +150°C
Lead Temperature (Soldering, 10 sec.). . . . . . . . . . . . . +300°C
All currents are positive into, negative out of the specified terminal. Consult Packaging Section of Databook for thermal limitations and considerations of packages.
Note 1: Voltages more negative than -0.4V can be tolerated if
current is limited to 50mA.
CONNECTION DIAGRAMS
ELECTRICAL CHARACTERISTICS:
Unless otherwise stated these specifications apply for TA= –40°C to +85°C for
UC2909; °0C to +70°C for UC3909; CT= 330pF, R
SET
= 11.5k, R10 = 10k, R
THM
= 10k, VCC= 15V, Output no load, R
STAT0
=
R
STAT1
= 10k, CHGENB = OVCTAP = VLOGIC, TA= TJ.
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Current Sense AMP (CSA) Section
V
ID
= CS+ – CS–
DC Gain CS– = 0, CS+ = -50mV; CS+ = –250mV 4.90 5 5.10 V/V
CS+ = 0, CS– = 50mV; CS–- = 250mV 4.90 5 5.10 V/V
V
OFFSET(VCSO
– V
CAO
) CS+ = CS– = 2.3V, CAO = CA– 15 mV
CMRR VCM= –0.25 to VCC – 2, 8.8 < VCC < 14 50 dB
VCM= –0.25 to VCC, 14 < VCC < 35 50 dB
V
OL
VID= –550mV, –0.25V < VCM < VCC–2,
IO= 500µA
0.3 0.6 V
V
OH
VID= +700mV, –0.25V < VCM < VCC–2,
IO= –250µA
5.2 5.7 6.2 V
Output Source Current V
ID
= +700mV, CSO = 4V –1 –0.5 mA
Output Sink Current VID= –550mV, CSO = 1V 3 4.5 mA
3dB Bandwidth VID= 90mV, VCM= 0V 200 kHz
LCC-28, PLCC-28 (Top View)
L, Q Packages
3
UC2909
UC3909
ELECTRICAL CHARACTERISTICS: Unless otherwise stated these specifications apply for T
A
= –40°C to +85°C for
UC2909; °0C to +70°C for UC3909; CT= 330pF, R
SET
= 11.5k, R10 = 10k, R
THM
= 10k, VCC= 15V, Output no load, R
STAT0
=
R
STAT1
= 10k, CHGENB = OVCTAP = VLOGIC, TA= TJ.
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Current Error Amplifier (CEA) Section
I
B
8.8V < VCC < 35V, V
CHGENB
= V
LOGIC
0.1 0.8 µA
V
IO
(Note 2) 8.8V < VCC < 35V, CAO = CA– 10 mV
A
VO
1V < VAO < 4V 60 90 dB
GBW TJ= 25°C, F = 100kHz 1 1.5 MHz
V
OL
IO= 250µA 0.4 0.6 V
V
OH
IO= –5mA 4.5 5 V
Output Source Current CAO = 4V –25 –12 mA
Output Sink Current CAO = 1V 2 3 mA
ICA–, I
TRCK_CONTROL
V
CHGENB
= GND 8.5 10 11.5 µA
Voltage Amplifier (CEA) Section
I
B
Total Bias Current; Regulating Level 0.1 1 µA
VIO(Note 2) 8.8V < VCC < 35V, VCM = 2.3V, VAO = VA– 1.2 mV
A
VO
1V < CAO < 4V 60 90 dB
GBW TJ= 25°C, F = 100kHz 0.25 0.5 MHz
V
OL
IO= 500µA 0.4 0.6 V
V
OH
IO= –500µA 4.75 5 5.25 V
Output Source Current CAO = 4V –2 –1 mA
Output Sink Current CAO = 1V 2 2.5 mA
VAO Leakage: High Impedance State V
CHGENB
= GND, STAT0 = 0 & STAT1 = 0,
VAO = 2.3V
–1 1 µA
Pulse Width Modulator Section
Maximum Duty Cycle CAO = 0.6V 90 95 100 %
Modulator Gain CAO = 2.5V, 3.2V 63 71 80 %/V
OSC Peak 3V
OSC Valley 1V
Oscillator Section
Frequency 8.8V < VCC < 35V 198 220 242 kHz
Thermistor Derived Reference Section
V
ID
= V
RTHM
– V
R10
Initial Accuracy, VAO (RTHM = 10k) VID= 0, R10 = RTHM =10k (Note 3) 2.2655 2.3 2.3345 V
VID= 0, R10 = RTHM =10k, –40°C ≤TA< 0°C
(Note 3)
2.254 2.3 2.346 V
Line Regulation V
CC
= 8.8V to 35V 3 10 mV
VAO RTHM = 138k, R10 = 10k 2.458 2.495 2.532 V
RTHM = 138k, R10 = 10k, -40°C ≤ TA< 0°C 2.445 2.495 2.545 V
RTHM = 33.63k, R10 = 10k 2.362 2.398 2.434 V
RTHM = 33.63k, R10 = 10k, -40°C ≤ T
A
< 0°C 2.350 2.398 2.446 V
RTHM = 1.014k, R10 = 10k 2.035 2.066 2.097 V
RTHM = 1.014k, R10 = 10k, -40°C ≤ TA< 0°C 2.025 2.066 2.107 V
Charge Enable Comparator Section (CEC)
Threshold Voltage As a function of VA– 0.99 1 1.01 V/V
Input Bias Current CHGENB = 2.3V –0.5 –0.1 µA
4
UC2909
UC3909
ELECTRICAL CHARACTERISTICS: Unless otherwise stated these specifications apply for T
A
= –40°C to +85°C for
UC2909; °0C to +70°C for UC3909; CT= 330pF, R
SET
= 11.5k, R10 = 10k, R
THM
= 10k, VCC= 15V, Output no load, R
STAT0
=
R
STAT1
= 10k, CHGENB = OVCTAP = VLOGIC, TA= TJ.
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Voltage Sense Comparator Section (VSC)
Threshold Voltage STAT0 = 0, STAT1 = 0, Function of V
REF
0.945 0.95 0.955 V/V
STAT0 = 1, STAT1 = 0, Function of V
REF
0.895 0.9 0.905 V/V
Over Charge Taper Current Comparator Section (OCTIC)
Threshold Voltage Function of 2.3V REF, CA- = CAO 0.99 1 1.01 V/V
Input Bias Current OVCTAP = 2.3V –0.5 –0.1 µA
Logic 5V Reference Section (VLOGIC)
VLOGIC VCC = 15V 4.875 5.0 5.125 V
Line Regulation 8.8V < V
CC
< 35V 3 15 mV
Load Regulation 0 < IO< 10mA 3 15 mV
Reference Comparator Turn-on Threshold 4.3 4.8 V
Short Circuit Current V
REF
= 0V 30 50 80 mA
Output Stage Section
I
SINK
Continuous 50 mA
I
PEAK
100 mA
V
OL
IO=50mA 1 1.3 V
Leakage Current V
OUT
=35V 25 µA
STAT0 & STAT1 Open Collector Outputs Section
Maximum Sink Current V
OUT
= 8.8V 6 10 mA
Saturation Voltage I
OUT
= 5mA 0.1 0.45 V
Leakage Current V
OUT
= 35V 25 µA
STATLV Open Collector Outputs Section
Maximum Sink Current V
OUT
= 5V 2.5 5 mA
Saturation Voltage I
OUT
= 2mA 0.1 0.45 V
Leakage current V
OUT
= 5V 3 µA
UVLO Section
Turn-on Threshold 6.8 7.8 8.8 V
Hysteresis 100 300 500 mV
I
CC
Section
I
CC
(run) (See Fig. 1) 13 19 mA
ICC(off) VCC = 6.5V 2 mA
Note 2: VIO is measured prior to packaging with internal probe pad.
Note 3: Thermistor initial accuracy is measured and trimmed with respect to VAO; VAO = VA–.
CA–: The inverting input to the current error amplifier.
CAO: The output of the current error amplifier which is
internally clamped to approximately 4V. It is internally
connected to the inverting input of the PWM comparator.
CS–, CS+: The inverting and non-inverting inputs to the
current sense amplifier. This amplifier has a fixed gain of
five and a common-mode voltage range of from –250mV
to +VCC.
CSO: The output of the current sense amplifier which is
internally clamped to approximately 5.7V.
CHGENB: The input to a comparator that detects when
battery voltage is low and places the charger in a trickle
charge state. The charge enable comparator makes the
output of the voltage error amplifier a high impedance
while forcing a fixed 10µA into CA– to set the trickle
charge current.
PIN DESCRIPTIONS
5
UC2909
UC3909
GND: The reference point for the internal reference, all
thresholds, and the return for the remainder of the device. The output sink transistor is wired directly to this
pin.
OVCTAP: The overcharge current taper pin detects
when the output current has tapered to the float threshold in the overcharge state.
OSC: The oscillator ramp pin which has a capacitor (C
T
)
to ground. The ramp oscillates between approximately
1.0V to 3.0V and the frequency is approximated by:
frequency
CR
TSET
=
••
1
12.
OUT: The output of the PWM driver which consists of an
open collector output transistor with 100mA sink capability.
R10: Input used to establish a differential voltage corresponding to the temperature of the thermistor. Connect
a 10k resistor to ground from this point.
RSET: A resistor to ground programs the oscillator
charge current and the trickle control current for the oscillator ramp.
The oscillator charge current is approximately
175.
R
SET
.
The trickle control current (I
TRCK_CONTROL
) is approxi-
mately
0115.
R
SET
.
RTHM: A 10k thermistor is connected to ground and is
thermally connected to the battery. The resistance will
vary exponentially over temperature and its change is
used to vary the internal 2.3V reference by –3.9mV/°C.
The recommended thermistor for this function is part
number L1005-5744-103-D1, Keystone Carbon Company, St. Marys, PA.
STAT0: This open collector pin is the first decode bit
used to decode the charge states.
STAT1: This open collector pin is the second decode bit
used to decode the charge states.
STATLV: This bit is high when the charger is in the float
state.
VA–: The inverting input to the voltage error amplifier.
VAO: The output of the voltage error amplifier. The up-
per output clamp voltage of this amplifier is 5V.
VCC: The input voltage to the chip. The chip is opera-
tional between 7.5V and 40V and should be bypassed
with a 1µF capacitor. A typical I
CC
vs. temperature is
shown in Figure 1.
VLOGIC: The precision reference voltage. It should be
bypassed with a 0.1µF capacitor.
Charge State Decode Chart
STAT0 and STAT1 are open collector outputs. The output is approximately 0.2V for a logic 0.
STAT1 STAT0
Trickle Charge 0 0
Bulk Charge 0 1
Over Charge 1 0
Float Charge 1 1
PIN DESCRIPTIONS (cont.)
Figure 1. ICCvs. temperature.
6
UC2909
UC3909
APPLICATION INFORMATION
A Block Diagram of the UC3909 is shown on the first
page, while a Typical Application Circuit is shown in Figure 2. The circuit in Figure 2 requires a DC input voltage
between 12V and 40V.
The UC3909 uses a voltage control loop with average
current limiting to precisely control the charge rate of a
lead-acid battery. The small increase in complexity of
average current limiting is offset by the relative simplicity
of the control loop design.
CONTROL LOOP
Current Sense Amplifier
This amplifier measures the voltage across the sense resistor RS with a fixed gain of five and an offset voltage of
2.3V. This voltage is proportional to the battery current.
The most positive voltage end of RS is connected to CSensuring the correct polarity going into the PWM comparator.
CSO = 2.3V when there is zero battery current.
RS is chosen by dividing 350mV by the maximum allow-
able load current. A smaller value for RS can be chosen
to reduce power dissipation.
Maximum Charge Current, Ibulk, is set by knowing the
maximum voltage error amplifier output, V
OH
= 5V, the
maximum allowable drop across RS, and setting the resistors RG1 and RG2 such that;
(1)
RG
RGVVLOGIC CA
V
VV
V
V
RS RS
RS
1
2
55
523
5
27
185
=
•
=
•
=
•
=
–– –.
.
.2••
IRS
BULK
The maximum allowable drop across RS is specified to
limit the maximum swing at CSO to approximately 2.0V
to keep the CSO amplifier output from saturating.
No charge/load current: V
CSO
= 2.3V,
Max charge/load current: V
max(CSO)
= 2.3V–2.0V = 0.3V
Voltage Error Amplifier:
The voltage error amplifier (VEA) senses the battery
voltage and compares it to the 2.3V – 3.9mV/°C thermis-
tor generated reference. Its output becomes the current
command signal and is summed with the current sense
amplifier output. A 5.0V voltage error amplifier upper
clamp limits maximum load current. During the trickle
charge state, the voltage amplifier output is opened (high
impedance output) by the charge enable comparator. A
trickle bias current is summed into the CA– input which
sets the maximum trickle charge current.
The VEA, VOH= 5V clamp saturates the voltage loop
and consequently limits the charge current as stated in
Equation 1.
During the trickle bias state the maximum allowable
charge current (ITC) is similarly determined:
(2)
ITC
IRG
RS
TRICK CONTROL
=
•
•
_
1
5
I
TRCK_CONTROL
is the fixed control current into CA–.
I
TRCK_CONTROL
is 10µA when R
SET
= 11.5k. See RSET
pin description for equation.
Current Error Amplifier
The current error amplifier (CA) compares the output of
the current sense amplifier to the output of the voltage
error amplifier. The output of the CA forces a PWM duty
cycle which results in the correct average battery current.
With integral compensation, the CA will have a very high
DC current gain, resulting in effectively no average DC
current error. For stability purposes, the high frequency
gain of the CA must be designed such that the magnitude of the down slope of the CA output signal is less
than or equal to the magnitude of the up slope of the
PWM ramp.
CHARGE ALGORITHM
Refer to Figure 3 in UC3906 Data Sheet in the data
book.
A) Trickle Charge State
STAT0 = STAT1 = STATLV = logic 0
When CHGNB is less than VREF (2.3V – 3.9mV/°C),
STATLV is forced low. This decreases the sense voltage
divider ratio, forcing the battery to overcharge (VOC).
(3)
()
VOC VREF
RS RS RS RS
RS RS
=•
++
()
()
||
123 4
34
||
During the trickle charge state, the output of the voltage
error amplifier is high impedance. The trickle control current is directed into the CA– pin setting the maximum
trickle charge current. The trickle charge current is defined in Equation 2.
B) Bulk Charge State
STAT1 = STATLV = logic 0, STAT0 = logic 1
As the battery charges, the UC3909 will transition from
trickle to bulk charge when CHGENB becomes greater
than 2.3V. The transition equation is
(4)
VT VREF
RS RS RS RS
RS RS RS
=•
++
+
(||)
(||)
1234
234
STATLV is still driven low.
7
UC2909
UC3909
UDG-95008-1
APPLICATION INFORMATION (cont.)
Figure 2. Typical application circuit
Pin numbers refer to J, N, DW packages.
8
UC2909
UC3909
During the bulk charge state, the voltage error amplifier
is now operational and is commanding maximum charge
current (I
BULK
) set by Equation 1. The voltage loop at-
tempts to force the battery to VOC.
C) Overcharge State
STAT0 = STATLV = logic 0, STAT1 = logic 1
The battery voltage surpasses 95% of VOC indicating
the UC3909 is in its overcharge state.
During the overcharge charge state, the voltage loop becomes stable and the charge current begins to taper off.
As the charge current tapers off, the voltage at CSO increases toward its null point of 2.3V. The center connection of the two resistors between CSO and VLOGIC sets
the overcurrent taper threshold (OVCTAP). Knowing the
desired overcharge terminate current (I
OCT
), the resistors
R
OVC1
and R
OVC2
can be calculated by choosing a value
of R
OVC2
and using the following equation:
(5)
()
RIRSR
OVC OCT OVC
12
18518=•••.
D) Float State
STAT0 = STAT1 = STATLV = logic 1
The battery charge current tapers below its OVCTAP
threshold, and forces STATLV high increasing the voltage sense divider ratio. The voltage loop now forces the
battery charger to regulate at its float state voltage (V
F
).
(6)
()
()
VV
RS RS RS
RS
FREF
=
++123
3
If the load drains the battery to less than 90% of VF, the
charger goes back to the bulk charge state, STATE 1.
OFF LINE APPLICATIONS
For off line charge applications, either Figure 3 or Figure
4 can be used as a baseline. Figure 3 has the advantage of high frequency operation resulting in a small isolation transformer. Figure 4 is a simpler design, but at
the expense of larger magnetics.
APPLICATION INFORMATION (cont.)
Figure 3. Off line charger with primary side PWM
UDG-95009
9
UC2909
UC3909
Figure 4. Isolated off line charger
APPLICATION INFORMATION (cont.)
UNITRODE CORPORATION
7 CONTINENTALBLVD. • MERRIMACK, NH 03054
TEL. (603) 424-2410 • FAX (603) 424-3460
UDG-95010
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