ML4873CR 데이터 시트보기 (PDF) - Micro Linear Corporation

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ML4873CR

Battery Power Control IC

Micro Linear Corporation 

ML4873

RT

RT

OSCILLATOR

RF1

VOUT

R1 C1

COMP

PWM

R

Q

F1

S

RF2

CSS

BURST

VREF

FDBK

EA

SOFT START

+5

CS1

1V

Q1

R

Q F2 S

OUT1

A1

SHOOT-THRU

PROTECTION

OUT2

A2

200mV

– + VIN

ILIM

ISENSE

BURST

Figure 3. Buck Regulator Block Diagram

Regulator A includes a pin which puts Regulator A into

“Burst mode”. When in “Burst mode” the regulator comes

on when the burst comparator is below its lower threshold

and goes off again when the output capacitor has charged

to the burst comparator‘s upper threshold. Burst mode is

useful for running the regulator at light modes, such as

memory keep-alive or “suspend” mode.

BURST

BIAS CKTS

ON

BUCK

REGULATOR

A

FDBK A

2.5V

Figure 4. Burst Mode Comparator and Logic

When burst mode is enabled the CSS discharge circuit

(Figure 3) is disabled. CSS is floating until CS1 is enabled

when a burst occurs. When probing the CSS pin in burst

mode, use a high impedance probe to prevent discharge

of the CSS pin from disturbing the circuit operation.

Selection of the external MOSFETs, output inductor and

capacitor determine the output capabilities of the

regulator. Output voltage is set by RF1 and RF2 where.

VOUT

=

2.5 × (RF1+ RF2)

RF2

(1)

The short circuit limit is set by external resistor RS.

ISHORT

CKT

≈

0.2

RS

(2)

CSS is discharged when the regulator is off or when the

voltage across RS exceeds 200mV. F2 ensures that CSS is

fully discharged. This circuit provides reliable output short

circuit protection with very little power wasted in the

sensing element. The error amplifier‘s output voltage is

limited to the voltage on the SOFT START pin. When CSS

is discharged, the regulator‘s duty cycle is 0.

250

200

150

100

50

0

100

150

200

250

300

350

400

RT KΩ

Figure 5. Oscillator Frequency vs. RT

6

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