ADP3804 Analog Devices, ADP3804 Datasheet - Page 5

• Manufacturer Part Number: ADP3804
• Description: High Frequency Switch Mode Li-Ion Battery Charger
• Manufacturer: Analog Devices

THEORY OF OPERATION
The ADP3804 combines a boosted synchronous switching
driver with programmable current control and accurate final
battery voltage control in a Constant Current, Constant Volt-
age (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 note-
book computer battery pack, three cells are in series giving a
total voltage of 12.6 V. The ADP3804 is available in three
versions, a fixed 12.525 V output, a fixed 12.6 V output and an
adjustable output. The adjustable output is useful for charging
batteries with slightly different chemistry that result in a final
battery voltage slightly higher or lower than 4.2 V/ cell.
Another requirement for safely charging Li-Ion batteries is
accurate control of the charge current. The actual charge cur-
rent depends on the number of cells in parallel within the bat-
tery pack. Typically this is in the range of 2 A to 3 A. The
ADP3804 provides flexibility in programming the charge cur-
rent 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 re-
duced for trickle charging.
The synchronous driver provides high efficiency when charging
at high currents. Efficiency is important mainly to reduce the
REV. PrI
BSTREG
0.1 F
100k
**R7
7.0V
C10
CCCV
VIN
SD
* ADP3804-12.6: R11 = SHORT, R12 = OPEN
** R7, OPEN IF CCCV FUNCTION IS NOT USED
2.2 F
C14
ADP3804
AGND
VREF + VREG
10
VCC
R13
CONTROL
LOGIC
UVLO
BIAS
220 F
BST
C15
100nF
C17
REG
6.0V
DRVH
+
0.1 F
C9
VREF
IRF7807
Q1
SYNCHRONOUS
REF
2.5V
SW
BOOSTED
DRIVER
DRVL
C7
200pF
SYNC
OSCILLATOR
PGND
200pF
Q2
IRF7807D2
CT
C6
Figure 1. Typical Application
COMP
22 H
L1
1 F
220 F
C8
C16
CS+
R8
56
+
–5–
g m 1
g m 2
R3
249
R CS
50m
22nF
C13
+
AMP
amount of heat generated in the charger, but also to stay within
the power limits of the AC adapter. With the addition of a
boosted high side driver, the ADP3804 drives two external
power NMOS transistors for a simple, lower cost power stage.
The ADP3804 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 1 has a differential input to amplify the voltage
drop across an external sense resistor R
mode range is from ground to VCC allowing current control in
short circuit and low drop-out conditions. The gain of AMP1 is
internally set to 25 V/V for low voltage drop across the sense
resistor. During CC mode, g
of AMP1 to be equal to the external voltage at the ISET pin.
By choosing R
charge currents can be programmed:
1
CS-
VREF
I
CHARGE
470nF
ADJ
R4
249
C1
SYS+
R1
10
CS
R SS1
10m
AMP
SYS-
25
2
V
and V
+
ISET
R
CS
R2
10
ISET
ADP3804-12.5
ADP3804-12.6
C2
470nF
2.5V
ISYS
SD
appropriately, a wide range of
m1
SYSTEM
DC/DC
forces the voltage at the output
6.81k
R5
7.5k
ISET
BAT
LIMIT
CS
R6
. The input common
ADP3804
*R11
412k
0.1%
*R12
102k
0.1%
BATTERY
12.6V
(1)