ADP3806JRU-REEL7 View Datasheet(PDF) - Analog Devices
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ADP3806JRU-REEL7 Datasheet PDF : 16 Pages
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ADP3806
THEORY OF OPERATION
The ADP3806 combines a bootstrapped synchronous switching
driver with programmable current control and accurate final
battery voltage control in a constant-current, constant-voltage
(CCCV) Li-Ion battery charger. High accuracy voltage control
is needed to safely charge Li-Ion batteries, which are typically
specified at 4.2 V ± 1% per cell. For a typical notebook computer
battery pack, three or four cells are in series, giving a total
voltage of 12.6 V or 16.8 V. The ADP3806 is available in three
versions, a selectable 12.525 V or 16.7 V output, a selectable
12.6 V or 16.8 V output, and an adjustable output. The
adjustable output can be programmed for a wide range of
battery voltages using two external precision resistors.
Another requirement for safely charging Li-Ion batteries is
accurate control of the charge current. The actual charge
current depends on the number of cells in parallel within the
battery pack. Typically, this is in the range of 2 A to 3 A. The
ADP3806 provides flexibility in programming the charge
current over a wide range. An external resistor is used to sense
the charge current and this voltage is compared to a dc input
voltage. This programmability allows the current to be changed
during charging. For example, the charge current can be
reduced for trickle charging.
The synchronous driver provides high efficiency when charging
at high currents. Efficiency is important mainly to reduce the
amount of heat generated in the charger but also to stay within
the power limits of the ac adapter. With the addition of a boot-
strapped high side driver, the ADP3806 drives two external
power NMOS transistors for a simple, lower cost power stage.
The ADP3806 also provides an uncommitted current sense
amplifier. This amplifier provides an analog output pin for
monitoring the current through an external sense resistor. The
amplifier can be used anywhere in the system that high side
current sensing is needed.
CHARGE CURRENT CONTROL
AMP1 in Figure 18 has a differential input to amplify the
voltage drop across an external sense resistor RCS. The input
common-mode range is from ground to VCC, allowing current
control in short-circuit and low dropout conditions. The gain of
AMP1 is internally set to 25 V/V for low voltage drop across the
sense resistor. During constant current (CC) mode, gm1 forces
the voltage at the output of AMP1 to be equal to the external
voltage at the ISET pin. By choosing RCS and VISET appropriately,
a wide range of charge currents can be programmed.
ICHARGE
=
VREF
25 × RCS
(1)
VIN
C14
2.2µF
1/2 Q1
FD56990A
R13 C15 +
10Ω 22µF –
C9
L1
22µH +
1/2 Q1
FD56990A
C16
22µF
–
RCS
40mΩ
R3
249Ω
C13
22nF
R4
249Ω
C1
470nF
RSS
10mΩ
SYSTEM
DC/DC
R1
2.2Ω
R2
2.2Ω
C2
470nF
BATTERY
12.6V/16.8V
100nF
VCC BST DRV SW DRVL PGND
CS+
CS– SYS+ SYS–
ISYS
BSTREG
7.0V
C10
0.1µF
SD
VREF + VREG
UVLO
BIAS
LOGIC
CONTROL
BOOTSTRAPPED
SYNCHRONOUS
DRIVER
SD
VREF
IN DRVLSD
DRVLSD
–
+
+
–
+–
AMP1
VTH
–
gm1
+
AMP2
2.5V
LIMIT
R111
412kΩ
0.1%
ISET
BAT
LC
R72
100kΩ
ADP3806
OSCILLATOR
–
gm2
+
VREF
SELECT
12.6V/16.8V
AGND
REG REF SYNC
CT
6.0V 2.5V
C7
C6
200pF 180pF
COMP
C8
0.22µF
R8
56Ω
R121
412kΩ
0.1%
C17
100nF
NOTES
1 ADP3806-12.6, ADP3806-12.5: R11 = SHORT, R12 = OPEN;
ADP3806, R11 = 412kΩ, R12 = 102kΩ, R14 = OPEN.
2 R7, OPEN IF LC FUNCTION IS NOT USED.
Figure 18. Typical Application
Rev. C | Page 10 of 16
BATSEL
R141
0Ω
R5
6.81kΩ
R6
7.5kΩ
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