Data Sheet

LTM8060F

analog.com

Rev. 0

21 of 43

Figure 51. Dual Channel Derating, VOUT = 5V CH1/CH3 ON, CH2/CH4 OFF, BIAS = 5V,

DC2820A-B Demo Board, TJ = 120°C, Burst Mode Operation

THEORY OF OPERATION

LTM8060F Overview

The LTM8060F is a quad standalone non-isolated step-down switching dc-to-dc power supply that can deliver a

peak current of up to 4A per channel. The continuous current is determined by the internal operating temperature.

It provides a precisely regulated output voltage programmable through one external resistor from 0.8V to 8V. The

input voltage range for VIN1 and VIN34 is 3V to 40V, while the input voltage range for VIN2 is 2V to 40V.

Given that the LTM8060F is a step-down converter, make sure that the input voltage is high enough to support the

desired output voltage and load current. The LTM8060F has a fixed fSW peak current mode architecture which

supports reliable clock interleaving. See Figure 52 for the Simplified Block Diagram.

The LTM8060F contains current mode controllers, power switching elements, power inductors, and a modest

amount of input and output capacitance. The LTM8060F is a fixed frequency pulse-width modulation (PWM)

regulator. The switching frequency is set by simply connecting the appropriate resistor value from the RTn pin

to GND.

Internal regulators provide power to the control circuitries. Bias regulators normally draw power from the VINn pin,

but if the BIASn pin is connected to an external voltage higher than 3.2V, bias power is drawn from the external

source (typically the regulated output voltage). This improves efficiency. Connect BIASn to GND if it is not used.

To enhance efficiency, the LTM8060F automatically switches to Burst Mode operation in light or no-load situations.

Between bursts, all circuitry associated with controlling the output switch is shut down, reducing the input supply

current to just a few µA.

The TRSSn node acts as an auxiliary input to the error amplifier. The voltage at FBn servos to the TRSSn voltage

until TRSSn goes above 0.8V. Soft start is implemented by generating a voltage ramp at the TRSSn pin using an

external capacitor, which is charged by an internal 2μA constant current. Alternatively, driving the TRSSn pin with a

signal source or resistive network provides a tracking function. Do not drive the TRSSn pin with a low-impedance

voltage source. See the Applications Information section for more details.

0LFM

AMBIENT TEMPERATURE (°C)

0

25

50

75

100

125

0

1

2

3

4

5

6

7

12VIN

24VIN

36VIN