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ADP3806JRUZ-REEL7 View Datasheet(PDF) - Analog Devices

Part Name
Description
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ADP3806JRUZ-REEL7
ADI
Analog Devices ADI
ADP3806JRUZ-REEL7 Datasheet PDF : 16 Pages
First Prev 11 12 13 14 15 16
ADP3806
Typical values of RCS range from 25 mΩ to 50 mΩ, and the
input range of ISET is from 0 V to 4 V. If, for example, a 3 A
charger is required, RCS could be set to 40 mΩ and VISET = 3 V.
The power dissipation in RCS should be kept below 500 mW. In
this example, the power is a maximum of 360 mW. Once RCS
has been chosen, the charge current can be adjusted during
operation with VISET. Lowering VISET to 125 mV gives a charge
current of 125 mA for trickle charging. The R3, R4, and C13
component s provide high frequency filtering for the current
sense signal.
FINAL BATTERY VOLTAGE CONTROL
As the battery approaches its final voltage, the ADP3806
switches from CC mode to constant voltage (CV) mode. The
change is achieved by the common output node of gm1 and gm2.
Only one of the two outputs controls the voltage at the COMP
pin. Both amplifiers can only pull down on COMP, such that
when either amplifier has a positive differential input voltage,
its output is not active. For example, when the battery voltage,
VBAT, is low, gm2 does not control COMP. When the battery
voltage reaches the desired final voltage, gm2 takes control of the
loop, and the charge current is reduced.
Amplifier gm2 compares the battery voltage to the internal
reference voltage of 2.5 V. In the case of the ADP3806-12.5 and
ADP3806-12.6, an internal resistor divider sets the selectable
final battery voltage.
When BATSEL is high, the final battery voltage is set to three
cells (12.6 V or 12.525 V). BATSEL can be tied to REG for this
state. When BATSEL is tied to ground, VBAT equals four cells
(16.8 V or 16.7 V). BATSEL has a 2 μA pull-up current as a fail-
safe to select three cells when it is left open.
ADP3806
BOOTSTRAPPED
SYNCHRONOUS DRIVER
MIN
IN
OFF
TIME
The reference and internal resistor divider are referenced to the
AGND pin, which should be connected close to the negative
terminal of the battery to minimize sensing errors.
In contrast, the ADP3806 requires external, precision resistors.
The divider ratio should be set to divide the desired final
voltage down to 2.5 V at the BAT pin
R11 = VBATTERY 1
(2)
R12 2.5 V
These resistors should have a parallel impedance of approximately
80 kΩ to minimize bias current errors. When the ADP3806 is in
shutdown, an internal switch disconnects the BAT pin as shown
in Figure 19. This disconnects the resistor (R11) from the
battery and minimizes leakage. The resistance of the internal
switch is less than 200 Ω.
ADP3806
SD
gm2
+
VREF
BATSEL
BAT
RR11
412k
0.1%
BATTERY
R12
102k
0.1%
Figure 19. Battery Sense Disconnect Circuit
OSCILLATOR AND PWM
The oscillator generates a triangle waveform between 1 V and
2.5 V. This is compared to the voltage at the COMP pin, setting
the duty cycle of the driver stage. When VCOMP is below 1 V, the
duty cycle is zero. Above 2.5 V, the duty cycle reaches its
maximum.
BSTREG
CMP3
BST
CBST
DRVH
Q1
SD
DELAY
CMP2
+
1V
CMP1
+
1V
DRVLSD
DELAY
Figure 20. Bootstrapped Synchronous Driver
Rev. C | Page 11 of 16
SW
DRVL
Q2
PGND
 

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