ADP3810AR-12.6 Просмотр технического описания (PDF) - Analog Devices

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производитель

ADP3810AR-12.6

Secondary Side, Off-Line Battery Charger Controllers

Analog Devices 

ADP3810/ADP3811

options could be used, or the ADP3811 could be substituted

= 00"" ....

9!1!!!!!!!!!

TA=+25'C

V'N 220VAC

= 10V !!!! !!!!! VCTRL 1V

. .... .... .... ....

II

II

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

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

turn to the VINsource and the other ground for the ADP3810

circuitry. Res separates the two grounds, and it is important to

keep them separate as shown.

01I%0 "" .... ........ .... ........ ........ ....

2VIDIV

OV

50mseclD..IV

The adjustable version of the ADPI148 is used in this circuit in-

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

into the VFBpin, which is set to regulate at VBATMAX+ 0.5 V.

Doing so provides a secondary, higher voltage limit without

interfering with normal circuit operation. The control output of

Figure 27. Output Voltage Transient Response to Battery

the ADP3810 is connected through a 560 Q resistor to the

Connect/Disconnect

SENSE+ input of the ADP1148. The current, loUT,adjusts the

OBSOLETE 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 ADPI148 is a high efficiency,synchro-

nous, step-down regulator that controls two external MOSFETs

as shown. Similar to the previous flyback circuit, the ADP38 10

controls the average charge current and the final battery voltage,

and the ADPI148 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

givesformulas for choosing the external components.

The resistor RSENSsEets the cycle by cycle current limit to 1.5 A,

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

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

ramp across RsENSE.Higher lOUTincreases the voltage on

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

tive feedback.

The circuit as shown can quickly and safely charge Lilon 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 Q sense resistor further lowers

the efficiency due to the 12x Res power loss at high output cur-

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

ADP3810 uses a 0.25 Q resistor, Res, to sense the battery cur-

through a 0.25 Q resistor. When the current increases above the

rent. As before, a 20 kQ resistor is needed between Res and the limit, the internal GM amplifier causes the output to go high.

Ves input of the ADP3810. The RC network from Ves to ground This puts more voltage across R8, increasing the current in Ql.

performs the dual function of filtering and compensation.

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

The voltage loop directly senses the battery voltage. Since the

ing the gate to source voltage and decreasing the charge current

ADP3810 is used in this circuit instead of the ADP3811, VSENSE to complete the feedback loop. Because the ADP3811 has a

is connected directly to the battery. The internal resistors set the current output, an external 1 ill resistor is needed from the

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

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

+V'N

VREF

VCTRL

(OV TO 1V)

VCC

VSENSE

OUT

VREF ADP3810

Vas

VCTRL

REF & CTRL

RTN

0.1pF

GND

V'N~

RTN \1

. COIL TRONICS CTX-684

..KRLSL.1-C1-0R068J

COMP

RC1

2kQ

CC1

1pF

+

;1PF

75kQ

V,N

P DRIVE

RC2

560Q

CC2

220nF

= OV NORMAL

>1.5V=SHUTDOWN

VFB

SHUTDOWN

SENSE+

ADP1148

SENSE-

C,

68pF

20kQ

N DRIVE

REV.0

Figure 28. High Efficiency Buck Battery Charger

-11-

t.L C'N

560Q ;100PF

L' RSENSE'

62pH 50 mQ I VBAT

100Q

I: 1000:F

-'N.

I

COUT'!:.

D1

1060040

220PF;

Rcs

0.25Q

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