ADP3810/ADP3811

–11–

REV. 0

10

0%

100

90

50msec/DIV

2V/DIV

10V

6V

0V

Figure 27. Output Voltage Transient Response to Battery

Connect/Disconnect

NONISOLATED TOPOLOGIES

Buck Switching Regulators

The ADP3810/ADP3811 and the ADP1148 can be combined

to create a high efficiency buck regulator battery charger as

shown in Figure 28. The ADP1148 is a high efficiency, synchro-

nous, step-down regulator that controls two external MOSFETs

as shown. Similar to the previous flyback circuit, the ADP3810

controls the average charge current and the final battery voltage,

and the ADP1148 controls the cycle by cycle current. The fol-

lowing discussion explains the functionality of the circuit but

does not go into detail on the ADP1148. For more information,

the ADP1148 data sheet details the operation of the device and

gives formulas for choosing the external components.

which is far enough above the 1 A average current of the

ADP3810 loop to avoid interfering but still provides a safe

maximum current to protect the external components. The

ADP3810 uses a 0.25

Ω resistor, R

rent. As before, a 20 k

Ω resistor is needed between R

performs the dual function of filtering and compensation.

The voltage loop directly senses the battery voltage. Since the

is connected directly to the battery. The internal resistors set the

battery voltage to 8.4 V in this case. Of course, other voltage

options could be used, or the ADP3811 could be substituted

with external resistors for a user set voltage. Notice the two

grounds in the circuit. One ground is for the high current re-

keep them separate as shown.

The adjustable version of the ADP1148 is used in this circuit in-

stead of a fixed output version. The output voltage is fed back

Doing so provides a secondary, higher voltage limit without

interfering with normal circuit operation. The control output of

the ADP3810 is connected through a 560

Ω resistor to the

dc level on the SENSE+ pin, which is added to the current

SENSE+ and reduces the duty cycle of the 1148, giving nega-

tive feedback.

The circuit as shown can quickly and safely charge LiIon batter-

ies while maintaining high efficiency. The efficiency of the

ADP1148 is only degraded slightly by the addition of the

ADP3810 and external circuitry. The 1.5 mA of supply current

lowers the overall efficiency by approximately 1%–2% for maxi-

mum output current. The 0.25

Ω sense resistor further lowers

the efficiency due to the I

2

× R

rents. See the efficiency discussion in the ADP1148 data sheet

for more information.

Linear Regulator

A third charging circuit is shown in Figure 29. In this case, the

switching supply is replaced with a linear regulator. The ADP3811

drives the gate of an N-channel MOSFET using an external

2N3904. As before, the ADP3811 senses the charge current

through a 0.25

Ω resistor. When the current increases above the

limit, the internal GM amplifier causes the output to go high.

This puts more voltage across R8, increasing the current in Q1.

As the current increases, the gate of M1 is pulled lower, reduc-

ing the gate to source voltage and decreasing the charge current

to complete the feedback loop. Because the ADP3811 has a

current output, an external 1 k

Ω resistor is needed from the

OUT pin to ground in order to convert the current to a voltage.

20k

Ω

100

Ω

2k

Ω

50 m

Ω

100µF

1µF

0.1µF

68pF

0.1µF

220nF

* COILTRONICS CTX-68-4

** KRL SL-1-C1-0R068J

0.1µF

GND

COMP

OUT

ADP3810

(0V TO 1V)

REF & CTRL

RTN

560

Ω

SHUTDOWN

P DRIVE

SENSE+

SENSE–

N DRIVE

S GND

P GND

1000pF

N CH

IRF7403

P CH

IRF7204

0V = NORMAL

>1.5V = SHUTDOWN

560

Ω

L*

62µH

220µF

100

Ω

BATTERY

1µF

RTN

ADP1148

D1

10BQ040

0.25

Ω

75k

Ω

10

k

Ω

Figure 28. High Efficiency Buck Battery Charger