1 Features

• Wide input range from 3.5V to 78V (85V absolute

maximum)

– Minimum 2.8V when V(BIAS) > 3.5V

• Output voltage from 3.3V to 78V

• Low shutdown IQ of 3μA

• Low operating IQ of 60μA

• 3% reverse current limit accuracy for precise

charging currents

• Average input and output current monitor or limiter

• Dynamic output voltage tracking for PWM or

analog input signals

• Power save mode (PSM) selectable for high light

load efficiency

• Two integrated high-voltage supply LDOs with

automatic selection

• Fixed frequency across all operating modes

(boost, buck-boost, buck)

– Forced PWM mode selectable

– Switching up to 1.8MHz for small solution and

component size

– External clock synchronization

• Spread spectrum operation selectable

• Adjustable undervoltage protection

• Hiccup overcurrent and short protection

2 Applications

• Non-isolated DC/DC supply (merchant DC/DC,

remote radio unit, motor drive control)

• Backup power systems (battery backup, fire

safety)

• Industrial PC (single board computer)

• Medical PSU (oxygen concentrator)

• Power over Ethernet (router)

• Solar power (solar charge controller)

3 Description

The LM51770x is a four switch buck-boost controller.

The device provides a regulated output voltage if

the input voltage is higher, equal, or lower than

the adjusted output voltage. In power save mode,

the device supports high efficiency with low output

loads due to its low quiescence currents. In power

save mode, the device supports high efficiency close

to 99% efficiency over the full range of the output

current. The LM51770x runs at a fixed switching

frequency, which is set through the RT or SYNC pin.

The switching frequency remains the same during

buck, boost, and buck-boost operation. The integrated

and optional average current monitor helps monitor

and limit input and output current of the LM51770x.

This feature also supports charging backup power

elements, like batteries or capacitors, with constant

current (CC) and constant voltage (CV).