Dual step-down controller with adjustable voltages PM6686

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Dual step-down controller with adjustable voltages, adjustable LDO and auxiliary charge pump controller for notebook.

Description
PM6686 is a dual step-down controller specifically designed to provide extremely high efficiency
conversion, with lossless current sensing technique. The constant on-time architecture assures fast load transient response and the embedded voltage feed-forward provides nearly constant switching frequency operation. Pulse skipping technique increases efficiency at very light load. Moreover a minimum switching frequency of 33 kHz is selectable to avoid audio noise issues. The PM6686 provides a selectable switching frequency, allowing three different values of switching frequencies for the two switching sections. The output voltages OUT1 and OUT2 can be programmed to regulate 1.5 V/5 V and 1.05 V/3.3 V outputs respectively or
can deliver two adjustable output voltages. An optional external charge pump can be monitored. This device embeds a linear regulator that can provide 3.3 V/5 V or an adjustable voltage from 0.7 V to 4.5 V output. The linear regulator provides up to 100 mA output current. LDO can be bypassed with the switching regulator outputs or with an external power supply (switchover function).
When in switchover, the LDO output can source up to 200 mA.

Features

■ 5.5 V to 28 V input voltage range
■ Dual fixed OUT1 = 1.5 V/5 V and OUT2 = 1.05 V / 3.3 V outputs or adjustable OUT1 = 0.7 V to 5.5 V and OUT2 = 0.7 V to 2.5 V outputs, ± 1.5% accuracy over valley regulation
■ Low-side MOSFETs' RDS(on) current sensing and programmable current limit
■ Constant ON-time control
■ Frequency selectable
■ Soft-start internally fixed at 2 ms and soft-stop
■ Selectable pulse skipping at light loads
■ Selectable minimum frequency (33 kHz) in pulse skip mode
■ Independent Power Good and EN signals
■ Latched OVP and UVP
■ Charge pump feedback
■ Fixed 3.3 V/5.0 V, or adjustable output 0.7 V to 4.5 V, ± 1.5% (LDO): 200 mA
■ 3.3 V reference voltage ± 2.0%: 5 mA
■ 2.0 V reference voltage ± 1.0%: 50 μA

Applications
■ Notebook computers
■ Main (3.3 V/5 V), chipset (1.5 V/1.05 V), DDR1/2/3, graphic cards power supply
■ PDAs, mobile devices, tablet PC or slates
■ 3-4 cells Li+ battery powered devices
PM6686.png
Typical operating characteristics
(TON = VCC (200 / 300 kHz), SKIP = GND (skip mode), LDOREFIN = SGND (LDO = 5 V), LDO_SW = OUT1, PVCC connected to LDO, VIN = 12 V, EN1-EN2-EN_LDO are high, no load unless specified). Measures performed on the demonstration kit (PM6686_SYSTEM and PM6686_CHIPSET) Efficiency traces: Green: VIN = 7 V, red: VIN = 12 V, blue: VIN = 19 V.


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