ADP3806JRU-12.6-RL Analog Devices Inc, ADP3806JRU-12.6-RL Datasheet - Page 12

• Manufacturer Part Number: ADP3806JRU-12.6-RL
• Description: IC CHARGER LI-ION 12.6V 24-TSSOP
• Manufacturer: Analog Devices Inc

Specifications of ADP3806JRU-12.6-RL

• Rohs Status: RoHS non-compliant
• Function: Charge Management
• Battery Type: Lithium-Ion (Li-Ion)
• Voltage - Supply: 13 V ~ 20 V
• Operating Temperature: 0°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 24-TSSOP (0.173", 4.40mm Width)
• Other names: ADP3806JRU-12.6RL

ADP3806
Shutdown
A high impedance CMOS logic input is provided to turn off the
ADP3806. When the voltage on SD is less than 0.8 V, the
ADP3806 is placed in low power shutdown. With the exception
of the system current sense amplifier, AMP2, all other circuitry
is turned off. The reference and regulators are pulled to ground
during shutdown and all switching is stopped. During this state,
the supply current is less than 5 mA. Also, the BAT, CS+, CS–,
and SW pins go to high impedance to minimize current drain
from the battery.
UVLO
Undervoltage lock-out, UVLO, is included in the ADP3806 to
ensure proper startup. As VCC rises above 1 V, the reference
and regulators will track VCC until they reach their final volt-
ages. However, the rest of the circuitry is held off by the UVLO
comparator. The UVLO comparator monitors both regulators
to ensure that they are above 5 V before turning on the main
charger circuitry. This occurs when VCC reaches 6 V. Monitor-
ing the regulator outputs makes sure that the charger circuitry
and driver stage have sufficient voltage to operate normally. The
UVLO comparator includes 300 mV of hysteresis to prevent
oscillations near the threshold.
Startup Sequence
During a startup from either SD going high or VCC exceeding
the UVLO threshold, the ADP3806 initiates a soft-start sequence.
The soft-start timing is set by the compensation capacitor at the
COMP pin and an internal 40 mA source. Initially, both DRVH
and DRVL are held low until VCOMP reaches 1 V. This delay
time is set by
For a 0.22 mF COMP capacitor, t
delay, the duty cycle is very low and then ramps up to its final
value with the same ramp rate given for t
V
duty cycle will be approximately 65%, corresponding to a V
of ~2 V. The time for the duty cycle to ramp from 0% at V
= 1 V to 65% at V
the charge current is equal to zero at first, DRVLSD is active
and DRVL will not turn on. However, if the BST capacitor is
discharged, DRVL will be forced on for a minimum on time
of 200 ns each clock period until the BST capacitor is charged
to greater than 4 V. Typically the BST capacitor is charged in five
to ten clock cycles.
Loop Feed Forward
As the startup sequence discussion shows, the response time at
COMP is slowed by the large compensation capacitor. To speed
up the response, two comparators can quickly feed forward around
the normal control loop and pull the COMP node down to limit
any overshoot in either short-circuit or overvoltage conditions.
The overvoltage comparator has a trip point set to 20% higher
than the final battery voltage. The overcurrent comparator thresh-
old is set to 180 mV across the CS pins, which is 15% above the
maximum programmable threshold. When these comparators
are tripped, a normal soft-start sequence is initiated. The over-
voltage comparator is valuable when the battery is removed
during charging. In this case, the current in the inductor causes
the output voltage to spike up, and the comparator limits the
maximum voltage. Neither of these comparators affects the loop
under normal charging conditions.
IN
is 16 V and the battery is 10 V when charging is started, the
t
DELAY
=
C
COMP
40 m
COMP
¥ 1
A
= 2 V is approximately 5 ms. Because
V
DELAY
is 5 ms. After this initial
DELAY
. For example, if
COMP
COMP
(4)
–12–
APPLICATION INFORMATION
Design Procedure
Refer to Figure 1, the typical application circuit, for the follow-
ing description. The design follows that of a buck converter.
With Li-Ion cells it is important to have a regulator with accu-
rate output voltage control.
Battery Voltage Settings
The ADP3806 has three options for voltage selection:
When using the fixed versions, R11 should be a short or 0 W
wire jumper and R12 should be an open circuit. When using the
adjustable version, the following equation gives the ratio of the
two resistors:
Often 0.1% resistors are required to maintain the overall accu-
racy budget in the design.
Inductor Selection
Usually the inductor is chosen based on the assumption that the
inductor ripple current is ± 15% of the maximum output dc
current at maximum input voltage. As long as the inductor used
has a value close to this, the system should work fine. The final
choice affects the trade-offs between cost, size, and efficiency.
For example, the lower the inductance, the size is smaller but
ripple current is higher. This situation, if taken too far, will lead
to higher ac losses in the core and the windings. Conversely, a
higher inductance results in lower ripple current and smaller
output filter capacitors, but the transient response will be slower.
With these considerations, the required inductance can be
found from
where the maximum input voltage V
minimum duty ratio D
of the output voltage to the input voltage, V
current is found from
the maximum peak-to-peak ripple is 30%, that is 0.3, and maxi-
mum battery current, I
For example, with V
3A, and T
Choosing the closest standard value gives L1 = 22 mH.
Output Capacitor Selection
An output capacitor is needed in the charger circuit to absorb
the switching frequency ripple current and smooth the output
voltage. The rms value of the output ripple current is given by
The maximum value occurs when the duty cycle is 0.5. Thus
1. 12.525 V/16.7 V as selectable fixed voltages
2. 12.6 V/16.8 V as selectable fixed voltages
3. Adjustable
L
DI
I
R
I
R
rms
rms_MAX
1 =
11
12
=
=
V
0 3 .
=
S
V
IN, MAX
fL
Ê
Á
Ë
= 4 ms, the value of L1 is calculated as 18.9 mH.
IN, MAX
V
¥
1 12
= 0 072
2 5
BAT
I
.
D
BAT, MAX
.
I
ˆ
˜
¯
–
D
IN, MAX
V
–
(
BAT
1
V
MIN
1–
BAT, MAX
IN, MAX
fL
. The duty ratio is defined as the ratio
D
¥
= 19 V, V
)
1
D
MIN
, is used.
¥
T
S
BAT
IN, MAX
= 12.6 V, I
BAT
is used with the
/V
IN
. The ripple
BAT,MAX
REV. B
=
(5)
(6)
(7)
(8)
(9)