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).