A multiphase DC/DC controller with 6-bit VID, ±1% VOUT accuracy and ±2.5%
phase current matching, the LTC3877 operates over an input voltage range of 4.5V to 38V and produces a fixed output voltage from 0.6V to 1.23V when using VID and up to 5V without VID. Up to 12 phases can be paralleled and clocked out-of-phase to minimize filtering. When outputs are paralleled, the LTC3877 maintains better than ±2.5% current mismatch between phases, making it appropriate for very high current requirements up to 300A. Applications include high current power distribution, redundant (n+1) supplies, industrial systems and processor power.
The device maintains ±1% output voltage accuracy (including internal resistor divider and differential remote sense amplifier errors) over a -40°C to 125°C temperature range. Dual onboard differential amplifiers enable remote output voltage sensing for both outputs. High step-down ratios at high operating frequencies are possible with its 40 nsec minimum on-time. The LTC3877 has a selectable fixed operating frequency from 250 kHz to 1MHz or it can be synchronised to an external clock. Onboard, 1.1-Ω all N-channel gate drivers minimise MOSFET switching losses.
The LTC3877 operates with true current mode control and can be used with very low DC resistance (DCR) power inductors down to 0.3 mΩ with its sensing scheme that enhances the signal-to-noise ratio of the current sense signal. This sensing scheme dramatically reduces the switching jitter normally associated with low DCR resistance applications and its adjustable current limit can be configured for very low sense voltages from 10 mV to 30 mV to minimise power loss. DCR temperature compensation maintains a constant current limit threshold over a broad temperature range. Additional features include adjustable soft-start or tracking, foldback current limit, short-circuit soft recovery, output overvoltage protection and two power-good output voltage signals.
In a 44-lead 7 x 7 mm QFN package, pricing starts at $3.94 (1000)
Linear Technology; www.linear.com/product/LTC3877
next page; feature list
Summary of Features: LTC3877
6-bit parallel VID inputs provides 10 mV output voltage resolution & ±1% accuracy over temperature
Less than ±2.5% current mismatch when both outputs are paralleled
Dual high speed differential remote VOUT sense amplifiers
Wide VIN range: 4.5V to 38V
VOUT range: 0.6V to 1.23V with VID control
VOUT range: 0.6V to 5V without VID control
Up to 12-phase operation
Selectable fixed operating frequency from 250 kHz to 1 MHz
40 nsec minimum on-time
Sub-milliohm DCR current sensing as low as 0.3 milliohms
Novel DCR sensing current mode control provides very low jitter
Adjustable current sense threshold from 10 mV to 150 mV
Output voltage tracking or programmable soft-start
Overvoltage protection and short-circuit soft recovery
Two power-good output signals
7 x 7 mm QFN-44 package