ADP3810AR-16.8 Analog Devices Inc, ADP3810AR-16.8 Datasheet - Page 10

• Manufacturer Part Number: ADP3810AR-16.8
• Manufacturer: Analog Devices Inc
• Type: Battery Chargerr

Specifications of ADP3810AR-16.8

• Output Voltage: 16.8V
• Operating Supply Voltage (min): 2.7V
• Operating Supply Voltage (max): 16V
• Operating Temp Range: -40C to 85C
• Package Type: SOIC N
• Mounting: Surface Mount
• Pin Count: 8
• Operating Temperature Classification: Industrial
• Lead Free Status / Rohs Status: Not Compliant

battery voltage is at least 1.5 V with a programmed charge cur-
The voltage limit of 10 V is approximately 10% above the maxi-
This limit gives a second level of protection without interfering
with -I1V/l1tcharge termination.
The final voltage and charge current accuracy is dependent
The charger circuit properly executes the charging algorithm ex-
hibiting stable operation regardless of battery conditions, includ-
voltages by modifying only the battery voltage sense divider. As
would be expected, circuit efficiency is best at high battery volt-
ADP3810/ADP3811
rent of 0.1 A. For a higher programmed charge current, the
battery voltagecan drop below 1.5 V, and Vee is stilI maintained
above 2.7 V. This is because of the additional energy in the
flyback transformer, which transfers more energy through the
stores the energy transferred through the 10 nF capacitor.
Secondary Side Component Calculations
Design Criteria:
Charging a 6 cell NiCad battery.
Max Individual Cell Voltage:
Max Battery Stack Voltage:
Max Charge Current:
Max Control Voltage:
RsFixedValue:
Picka Valuefor Rl:
mum fully charged voltage when -!:N/l1t termination is used.
Component Value Calculations:
Current Sense Resistor:
Battery Divider, R2:
upon the resistor tolerances. Choose appropriate tolerances for
the desired accuracy. One percent accuracy is recommended.
Charger Performance Summary
ing an open circuit load. The circuit can charge to other battery
ages. Replacing the output blocking rectifier diode with a
Schottky would improve efficiency if the Schottky's leakage
could be tolerated, and its reverse voltage rating met the appli-
cation requirement.
Figure 24. Charge Current vs. Battery Voltage at Four Set-
10 nF capacitor to Vee. The 22
tings for the Flyback Charger in Figure 23
J
....
0.9
0.8
0.7
0.6
0.4
0.3
0.2
0.1
0.0
1.0
0.5
2
-
-
3
VCTRL
VCTRL = 0.5V
VCTRL
VCTRL=0.125V
4
I
I
I
I
= 1.0V
=0.25V
.J.
Res
=
R2 = VREFX R1/(VOMAX-VREF)
R2
20.15 kQ, Pick 20.0 k.Q
I
0.25 W, 1%, 0.5 W
=
=
VeElLMAX
VOMAX
10MAX
VeTRL
Rs
Rl
6
2 x 80.6 k.Q/(lOV-2 V)
VeTRLI(4
Your
~
=
=
bypass capacitor on Vee
20 k.Q
7
80.6 k.Q
=
=
=
1A
1 V (for IoMAX
6 x 1.67 V
=
8
x 10MAx)
1.67 V
10
=
=
10 V
=
1/(4 xl)
11
=
1 A)
-10-
The Battery Charge Current vs. Battery Voltage characteristics
for four different charge current settings are given in Figure 24.
The high gain of the internal amplifiers ensures the sharp transi-
fast charging times.
The transient performance for various turn-on and turn-off con-
nected. As shown, the output voltage quickly rises and over-
battery is connected, but the loop quickly takes control and lim-
battery is removed, the current quickly returns to zero. The
with the switching of the PWM. The time scale is too slow to
when a battery stack charged to 6 V is connected and then dis-
voltage immediately goes to 6 V. When the battery is discon-
nected, the voltage returns to the programmed float voltage of
tion between current mode and voltage mode regardless of the
charge current setting. The fact that the current remains at full
charging until the battery is very close to its final voltage ensures
ditions is detailed in Figures 25, 26 and 27. Figure 25 shows
the output voltage when power is applied with no battery con-
shoots its set voltage. The internal comparator responds to this
and clamps the voltage giving a quick recovery. Without the in-
ternal comparator, an external zener would be required to clamp
the voltage to the LED anode. Figure 26 shows the battery cur-
rent when connecting and disconnecting a battery. The actual
trace shown is the voltage across Res, which is negative for cur-
rent flowing into the battery. There is an overshoot when the
its the average current to the programmed 0.75 A. When the
solid band on the scope is due to the current rising and falling
show the detail of this. Figure 27 shows the output voltage
connected. As expected, when the battery is connected, the
internal comparator.
10 V. Again, a small overshoot is present that is clamped by the
Figure 25. Flyback Charger Output Voltage Transient at
Power Turn On, No Battery Attached
Figure 26. Charge Current Transient Response to Battery
Connect/Disconnect
-200mV
O.OV
10V
OV
10
9
o...
00....
9=;
10
0
I
",...
!
.... ....... ........ .... .... ........ ....
.... .... .... .... .... .... .... .... ....
O.2V1DD!I
'V,N=220VAC ..
.... .... .... .... .... .... .... ....
TA
2VIDIV
NO BATTERY
=
+25°C
....
TA=+25°C
VCTRL
V,N=220VAC
....
II
20mseclDIV
= O.775V
.... ....
O.I..seclDIV
n
II
II:
-==
....
....
REV. 0