Preliminary

Rev.01

9/16

EP1551

Functional Block Diagram

Figure 7. Block Diagram for EP1551

Pin Description

PIN

NAME

FUNCTION

1

COMP1

Auxiliary Controller 1 Compensation Node. Connect a series RC from COMP1 to GND to

compensate the control loop. COMP1 is actively driven to GND in shutdown and thermal

limit.

2

FB1

Auxiliary Controller 1 Feedback Input. For 5V output, short FBSEL1 to GND and

connect FB1 to the output voltage. For other output voltages, connect FBSEL1 to

OUTSU and connect a resistive voltage-divider from the Step-up converter output to

FB1 to GND. The FB1 feedback threshold is then 1.25V. This pin is high impedance in

shutdown.

3

PGNDA

Power Ground. Connect PGNDA and PGNDB together and to GND with short trace as

close to the IC as possible.

4

LXSD

Step-down Converter Power-Switching Node. Connect LXSD to the Step-down

converter inductor. LXSD is the drain of the P-channel switch and N-channel

synchronous rectifier. LXSD is high impedance in shutdown.

5

INSD

Step-down Converter Input. INSD can connect to OUTSU, effectively making OUTSD a

buck-boost output from the battery. Bypass to GND with a 1µF ceramic capacitor if