LTC4012-1 datasheet(17/28 Pages) LINER

17 / 28 page

4012f

LTC4012/

LTC4012-1/LTC4012-2

APPLICATIONS INFORMATION

The value of RPROG controls the maximum value of charge

current which can be programmed (Q1 continuously on).

PWM of the Q1 gate voltage changes the value of RPROG

to produce lower currents. The frequency of this modula-

tion should be higher than a few kHz, and CPROG must be

increased to reduce the ripple caused by switching Q1. In

addition, it may be necessary to increase loop compensa-

tion capacitance connected to ITH to maintain stability or

prevent large current overshoot during start-up. Selecting

a higher Q1 PWM frequency (≈10kHz) will reduce the need

to change CPROG or other compensation values.Charge

current will be proportional to the duty cycle of the PWM

input on the gate of Q1.

Programming LTC4012 Output Voltage

See Table 2 for approximate resistor values for R2.

RR A R B

12085

⎛

⎝

⎜

⎞

⎠

⎟

VBAT

–,

Selecting R2 to be less than 50k and the sum of R1 and

R2 at least 200k or above, achieves the lowest possible

error at the VFB sense input. Note that sources of error

such as R1 and R2 tolerance, FBDIV RON or VFB input

impedance are not included in the speciﬁcations given in

the Electrical Characteristics. This leads to the possibil-

ity that very accurate (0.1%) external resistors might be

required. Actually, the temperature rise of the LTC4012 will

rarely exceed 50°C at the end of charge, because charge

current will have tapered to a low level. This means that

0.25% resistors will normally provide the required level of

overall accuracy. Table 2 gives recommended values for

R1 and R2 for popular lithium-ion battery voltages. For

values of R1 above 200k, addition of capacitor CZ may

improve transient response and loop stability. A value of

10pF is normally adequate.

Table 2. Programming Output Voltage

VBAT

(V)

R1 (0.25%)

(kΩ)

R2A (0.25%)

(kΩ)

R2B (1%)*

(Ω)

4.1

165

–

4.2

167

67.3

200

8.2

162

–

8.4

169

28.4

–

12.3

301

32.8

–

12.6

294

31.2

–

16.4

284

22.6

–

16.8

271

–

20.5

316

19.8

–

298

18.2

–

24.6

298

15.4

–

25.2

397

–

*To Obtain Desired Accuracy Requires Series Resistors For R2.

Figure 5. Programming Output Voltage

BAT

FBDIV

85Ω

TYPICAL

VFB

LTC4012

R2A

R2B*

4012 F05

GND

(EXPOSED PAD)

*OPTIONAL TRIM RESISTOR

Figure 5 shows the external circuit for programming the

charger voltage when using the LTC4012. The voltage is

then governed by the following equation:

RR A R B

BAT =

()

120851

.•

LTC4012-1 bảng dữ liệu(PDF) 17 Page - Linear Technology

LTC4012-1 bảng dữ liệu(HTML) 17 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

bảng dữ liệu tải về

Link URL