LTC4010 datasheet(13/24 Pages) LINER

13 / 24 page

LTC4010

4010fb

the average current through RSENSE. The ITH output of

the error amplifier is a scaled control current for the input

of the PWM comparator CC. The ITH • R3 product sets a

peak current threshold for CC such that the desired aver-

age current through RSENSE is maintained. The current

comparator output does this by switching the state of the

SR latch at the appropriate time.

At the beginning of each oscillator cycle, the PWM clock

sets the SR latch and the external P-channel MOSFET is

switched on (N-channel MOSFET switched off) to refresh

the current carried by the external inductor. The inductor

current and voltage drop across RSENSE begin to rise

linearly. During normal operation, the PFET is turned

off (NFET on) during the cycle by CC when the voltage

difference across RSENSE reaches the peak value set by

the output of EA. The inductor current then ramps down

linearly until the next rising PWM clock edge. This closes

the loop and maintains the desired average charge current

in the external inductor.

Low Dropout Charging

After charging is initiated, the LTC4010 does not require

that VCC remain at least 500mV above BAT because situ-

ations exist where low dropout charging might occur. In

one instance, parasitic series resistance may limit PWM

headroom (between VCC and BAT) as 100% charge is

reached. A second case can arise when the DC adapter

selected by the end user is not capable of delivering the

current programmed by RSENSE, causing the output volt-

age of the adapter to collapse. While in low dropout, the

LTC4010PWMrunsnear100%dutycyclewithafrequency

that may not be constant and can be less than 550kHz.

The charge current will drop below the programmed value

to avoid generating audible noise, so the actual charge

delivered to the battery may depend primarily on the

LTC4010 charge timer.

Internal Die Temperature

The LTC4010 provides internal overtemperature detection

to protect against electrical overstress, primarily at the

FET driver outputs. If the die temperature rises above this

thermal limit, the LTC4010 stops switching and indicates

a fault as previously discussed.

operaTion (Refer to Figure 1)

LTC4010 датащи(PDF) 13 Page - Linear Technology

LTC4010 датащи(HTML) 13 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

датащи скачать

ссылки URL