August 2005

11

MIC5156/5157/5158

MIC5156/5157/5158

Micrel, Inc.

GND

S

EA

MIC5158

G

EN

R1

R2

D

R3

R4

Figure 5. Battery Charger Concept

Uninterruptible Power Supply

The MIC5157 and two N-channel MOSFETs provide battery

switching for uninterruptible power as shown in figure (6).

Two MOSFETs are placed source-to-source to prevent cur-

rent flow through their body diodes when switched off. The

Super LDO regulator is continuously enabled to achieve

fast battery switch-in. Careful attention must be paid to the

ac-line monitoring circuitry to ensure that the output voltage

does not fall below design limits while the battery is being

switched in.

Line

Battery

S

G

MIC5158

D

EN

GND

EA

1N4148

Uninterruptable

DC

D

S

D

G

S

G

MOSFET body diodes

shown for clarity

Off-line

Power Supply

AC

Line

Q1

Q2

40V max.

Figure 6. UPS Power Supply Concept