ADP3810AR-12.6 データシートの表示（PDF） - Analog Devices
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ADP3810AR-12.6 Datasheet PDF : 14 Pages
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ADP3810/ADP3811
240
VC='+10V
I
200 I-
TA = +25°C
RL= 1kQ
~'.". 160
I
~ 120
1=
z
-0:
580
r
40
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r-U
5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0
- OUTPUT GAIN (VOUr'VCDMP)
VN
0.25
I VCC+10VI
ILOAD =SmA
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0I I I I I I I
-SO -25 0 25 50 75 100
TEMPERATURE-oC
OBSOLE= T= E Figure 20. Output Gain (VouTNcOMP)
Distribution
Figure 21. Output Gain (VOUrlVCOMP)
vs. Vcc
Figure 22. VSATVS.Temperature
APPLICATIONS SECTION
Functional Description
The ADP3810 and ADP3811 are designed for charging NiCad,
NiMH and Lilon batteries. Both parts provide accurate voltage
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
linear regulator. In all cases, the ADP38 I0/ADP38 I I maintains
accurate control of the current and voltage loops, enabling the
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
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
feedback loop comprised of Res, R3, GMI, the external dc-dc
converter and a dc voltage at the VCTRLinput. The actual
charge current is set by the voltage, VCTRLa,nd is dependent
upon the choice for the values of Res and R3 according to the
formula below:
I R3
IcHARGE=-Rxe-xsVC810RkLQ
Typical values are Res 0.25 Q and R3 20 kg, which result
later in this data sheet.
in a charge current of 1.0 A for a control voltage of 1.0 V. The
The ADP3810 and ADP3811 contain the following blocks
.(shown in Figure I):
Two "GM" type error amplifiers control the current loop
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
ground, forcing the Vcs pin to a virtual ground.
. (GMI) and the voltage loop (GM2).
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.
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
applications. The dc-dc converter must have a control scheme
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-
. age, VCTRL,to provide a high impedance input.
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
The resistor Res converts the charge current into the voltage at
VRcs, and it is this voltage that GMI is regulating. The voltage
at VRcsis equal to -(R3/80 kQ) VCTRL'When VCTRLequals
1.0 V, VRcsequals -250 mY. IfVRcs falls below its pro-
grammed level (i.e., the charge current increases), the negative
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
= (VREF 2.000 V):
VBAT =2.000VX(;~+I)
above VREF'This clamp shuts down the dc-dc converter to
If the battery voltage rises above its programmed voltage,
quickly recover from overvoltage transients and protect ex-
VSENSEis pulled above VREF' This causes GM2 to source more
ternal circuitry.
current, raising the CaMP node voltage and loUT' As with the
-6-
REV. 0
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