ML4873CR データシートの表示（PDF） - Micro Linear Corporation

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ML4873CR

Battery Power Control IC

Micro Linear Corporation 

ML4873

150

120

125

100

100

tRISE

75

80

tRISE

60

50

tFALL

25

40

tFALL

20

0

0

500

1000

1500

LOAD CAPACITANCE (pF)

Figure 6. OUT1 Rise and Fall Time vs. Load CLOAD

ADAPTER SWITCH

This function is provided by a comparator whose output

(VG5) is pulled to VGT when VADAPTER goes above 2.5V.

By connecting an N-Channel MOSFET gate to VG5, the

system can run from the battery without the loss

associated with a diode. When the AC adapter is plugged

in, the voltage on pin 3 goes high, VG5 swings low, and

the system runs from the AC adapter. This circuit functions

in all modes of IC operation except SLEEP, when the VG5

output goes low.

12V LINEAR REGULATOR

The 12V regulator includes a shut-off pin. To operate the

regulator as a low drop-out regulator, a separate 12VBIAS

pin is provided. If this pin is 1.5V higher than V12 IN, the

output transistor can be driven to saturation. Input for this

regulator may come from either VIN (for high voltage

battery packs) or from a coupled inductor winding as

shown in Figure 8. If the low drop-out feature is not

necessary, V12 BIAS can be tied to V12 IN.

VGT

OUT1

B1

VIN

B2

OUT2

VIN

RS

V12 IN

D1

L2

VOUT

0

0

500

1000

1500

LOAD CAPACITANCE (pF)

Figure 7. OUT2 Rise and Fall Time vs. Load CLOAD

APPLICATIONS

BUCK REGULATOR INDUCTOR

Inductors are specified with three main parameters;

inductance (L), maximum current (IOUT(MAX)), and DC

resistance (RL).

Inductance for a given set of requirements can be

calculated using the following:

L = (VIN − VOUT) ×  DF 

(3)

(2) × (IOUT(MIN))

In this equation, D is the duty cycle, and F is the switching

frequency.

Selecting the inductor value using this formula ensures

that the inductor stays in the continuous current mode,

and never goes discontinuous at light loads (IOUT(MIN)).

This is important, as high current spikes occur and losses

go up when operating in the discontinuous mode.

A good rule of thumb for choosing inductor core size is to

make sure that the maximum output current of the

regulator doesn‘t exceed 80% of the maximum current

rating of the inductor. Otherwise, core saturation may

occur. This is especially important for ferrites, which have

a harder saturation characteristic than powdered iron

cores.

In order to distribute conduction losses evenly among all

components, the DC resistance should be selected to be

1/4 of the sum of the RDSONs of the power MOSFETs.

Figure 8. Coupled Inductor to generated V12 IN

7

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