ADP3810AR-16.8 Analog Devices Inc, ADP3810AR-16.8 Datasheet - Page 6

• Manufacturer Part Number: ADP3810AR-16.8
• Manufacturer: Analog Devices Inc
• Type: Battery Chargerr

Specifications of ADP3810AR-16.8

• Output Voltage: 16.8V
• Operating Supply Voltage (min): 2.7V
• Operating Supply Voltage (max): 16V
• Operating Temp Range: -40C to 85C
• Package Type: SOIC N
• Mounting: Surface Mount
• Pin Count: 8
• Operating Temperature Classification: Industrial
• Lead Free Status / Rohs Status: Not Compliant

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The ADP3810 and ADP3811 contain the following blocks
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ADP3810/ADP3811
APPLICATIONS SECTION
Functional Description
NiMH and Lilon batteries. Both parts provide accurate voltage
linear regulator. In all cases, the ADP38 I0/ADP38 I I maintains
use of a low cost, industry standard dc-dc converter without
compromising system performance. Detailed realizations of
complete circuits including the dc-dc converter are included
later in this data sheet.
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.
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The ADP3810 and ADP3811 are designed for charging NiCad,
sense and current sense circuitry to control the charge current
and final battery voltage. Figure I shows a simplified battery
charging circuit with the ADP3810/ADP3811 controlling an
external dc-dc converter. The converter can be one of many
different types such as a Buck converter, Flyback converter or a
accurate control of the current and voltage loops, enabling the
(shown in Figure I):
Figure
Distribution
A current limited buffer stage (GM3) provides a current out-
put, loUT,to control an external dc-dc converter. This out-
put can directly drive an optocoupler in isolated converter
such that higher lOUTresults in lower duty cycle. If this is
not the case, a simple, single transistor inverter can be used
for control phase inversion.
An amplifier buffers the charge current programming volt-
An UVLO circuit shuts down the GM amplifiers and the
output when the supply voltage (Vcd fallsbelow 2.7 V. This
protects the charging system from indeterminate operation.
A transient overshoot comparator quickly increases loUT
when the voltage on the "+" input of GM2 rises over 120 mV
above VREF'This clamp shuts down the dc-dc converter to
quickly recover from overvoltage transients and protect ex-
ternal circuitry.
580
Two "GM" type error amplifiers control the current loop
A common CaMP node is shared by both GM amplifiers
such that an RC netWork at this node helps compensate both
control loops.
A precision 2.0 V reference is used internally and is available
externally for use by other circuitry. The O.IIIF bypass ca-
pacitor shown is required for stability.
applications. The dc-dc converter must have a control scheme
age, VCTRL,to provide a high impedance input.
~
'"
~
1=
z
-0:
..
(GMI) and the voltage loop (GM2).
I
240
200
160
120
40
0
5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0
I- T
20.
VC='+10V
RL= 1kQ
A
OUTPUT GAIN
= +25°C
Output
r-U
r
(VOUr'VCDMP)
Gain (VouTNcOMP)
I
-
VN
Figure 21. Output Gain (VOUrlVCOMP)
vs. Vcc
-6-
The resistor Res converts the charge current into the voltage at
VRcs, and it is this voltage that GMI is regulating. The voltage
input of GMI goes slightly below ground. This causes the out-
put of GMI to source more current and drive the CaMP node
high, which forces the current, lOUT,to increase. A higher loUT
decreases the drive to the dc-dc converter, reducing the charg-
ing current and balancing the feedback loop.
As the battery approaches its final charge voltage, the voltage
loop takes over. The system becomes a voltage source, floating
the battery at constant voltage thereby preventing overcharging.
The constant voltage feature also protects the circuitry that is
actually powered by the battery from overvoltage if the battery is
removed. The voltage loop is comprised of RI, R2, GM2 and
the dc-dc converter. The [mal battery voltage is simply set by
the ratio of RI and R2 according to the following equation
If the battery voltage rises above its programmed
VSENSE is pulled above VREF' This causes GM2 to source more
current, raising the CaMP
feedback loop comprised of Res, R3, GMI, the external dc-dc
upon the choice for the values of Res and R3 according to the
formula below:
Typical values are Res
ground, forcing the Vcs pin to a virtual ground.
at VRcsis equal to -(R3/80 kQ) VCTRL'When VCTRL equals
grammed level (i.e., the charge current increases), the negative
(VREF
Description of Battery Charging Operation
The IC based system shown in Figure I charges a battery with a
dc current supplied by a dc-dc converter, which is most likely a
switching type supply but could also be a linear supply where
feasible. The value of the charge current is controlled by the
converter and a dc voltage at the VCTRL input. The actual
charge current is set by the voltage, VCTRL, and is dependent
in a charge current of 1.0 A for a control voltage of 1.0 V. The
80 kQ resistor is internal to the IC, and it is trimmed to its ab-
solute value. The positive input of GMI is referenced to
1.0 V, VRcsequals -250 mY. IfVRcs falls below its pro-
=
2.000 V):
IcHARGE =-x-xVC1RL
VBAT =2.000VX(;~+I)
=
z~
0'0
1=>
-0:1
II: I- 0.15
::>"
I- <II
-0:>
"'oj
!:i~
"'I-
I-.J
::>0
0>
0.25 Q and R3
Figure 22. VSATVS.Temperature
node voltage and loUT' As with the
Res 80 kQ
0.20
0.10
0.05
0.25
I
0
-SO
I
I
VCC+10VI
ILOAD
R3
-25
I
=
SmA
TEMPERATURE-oC
=
I
0
20 kg, which result
25
I
I
voltage,
50
I
REV. 0
75
I
100
I