MIC79050 datasheet(12/20 Pages) MICREL

12 / 20 page

MIC79050

Micrel

MIC79050

June 2000

below the nominal output voltage, the output will follow the

input, less the saturation voltage drop of the pass element. If

the cell draws more than the maximum output current of the

device, the output will be pulled low, charging the cell at

600mA to 700mA current. If the input is a fixed source with a

low output impedance, this could lead to a large drop across

the MIC79050 and excess heating. By driving the feedback

pin with an external PWM-circuit, the MIC79050 can be used

to pulse charge the battery to reduce power dissipation and

bring the device and the entire unit down to a lower operating

temperature. Figure 5 shows a typical configuration for a

PWM-based pulse-charging topology. Two circuits are shown

in Figure 5: circuit a uses an external PWM signal to control

the charger, while circuit b uses the MIC4417 as a low duty-

cycle oscillator to drive the base of Q1. (Consult the battery

manufacturer for optimal pulse-charging techniques).

Li-Ion

Cell

4.7

µF

BAT

GND

MIC79050-4.2BMM

VIN

External PWM

Figure 5A.

Li-Ion

Cell

4.7

µF

200pF

Ω

40k

Ω

BAT

GND

MIC79050-4.2BMM

VIN=4.5V to 16V

MIC4417

Figure 5B. PWM Based Pulse-charging

Applications

Figure 6 shows another application to increase the output

current capability of the MIC79050. By adding an external

PNP power transistor, higher output current can be obtained

while maintaining the same accuracy. The internal PNP now

becomes the driver of a darlington array of PNP transistors,

obtaining much higher output currents for applications where

the charge rate of the battery is much higher.

BAT

4.7

µF

GND

MIC79050-4.2BMM

Figure 6. High Current Charging

Regulated Input Source Charging

When providing a constant-current, constant-voltage, charger

solution from a well-regulated adapter circuit, the MIC79050

can be used with external components to provide a constant

voltage, constant-current charger solution. Figure 7 shows a

configuration for a high-side battery charger circuit that

monitors input current to the battery and allows a constant

current charge that is accurately terminated with the

MIC79050. The circuit works best with smaller batteries,

charging at C rates in the 300mA to 500mA range. The

MIC7300 op-amp compares the drop across a current sense

resistor and compares that to a high-side voltage reference,

the LM4041, pulling the feedback pin low when the circuit is

in the constant-current mode. When the current through the

resistor drops and the battery gets closer to full charge, the

output of the op-amp rises and allows the internal feedback

network of the regulator take over, regulating the output to

4.2V.

BAT

GND

MIC79050-4.2BMM

SD101

4.7

µF

0.01

µF

MIC7300

LM4041CIM3-1.2

16.2k

221k

10k

Figure 7. Constant Current,

Constant Voltage Charger

Simple Charging

The MIC79050 is available in a three-terminal package,

allowing for extremely simple battery charging. When used

with a current-limited, low-power input supply, the MIC79050-

4.2BS completes a very simple, low-charge-rate, battery-

charger circuit. It provides the accuracy required for termina-

tion, while a current-limited input supply offers the constant-

current portion of the algorithm.

Thermal Considerations

The MIC79050 is offered in three packages for the various

applications. The SOT-223 is most thermally efficient of the

three packages, with the power SOP-8 and the power MSOP-8

following suit.

Power SOP-8 Thermal Characteristics

One of the secrets of the MIC79050’s performance is its

power SO-8 package featuring half the thermal resistance of

a standard SO-8 package. Lower thermal resistance means

more output current or higher input voltage for a given

package size.

Lower thermal resistance is achieved by joining the four

ground leads with the die attach paddle to create a single-

piece electrical and thermal conductor. This concept has

MIC79050 датащи(PDF) 12 Page - Micrel Semiconductor

MIC79050 датащи(HTML) 12 Page - Micrel Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

датащи скачать

ссылки URL