PM6686 datasheet(24/50 Pages) STMICROELECTRONICS

24 / 50 page

Device description

PM6686

24/50

Doc ID 15281 Rev 4

Device description

The PM6686 is a dual step down controller dedicated to provide logic voltages for notebook

computers. It offers several operating configurations: it combines two synchronous buck

controllers, an internal linear regulator (LDO), two voltage references and a charge pump

controller.

Each buck controller is based on constant on time (COT) architecture. This type of control

offers a very fast load transient response with a minimum external components count.

The two switching sections (SMPS) generate two output voltages OUT1 and OUT2 that

regulate adjustable voltages. A fixed output voltage configuration can also be selected,

reducing further the external components count because no external resistor divider is

needed.

In fixed mode, OUT1 provides 5 V or 1.5 V; in adjustable mode OUT1 can regulate an output

voltage between 0.7 V and 5.5 V. In fixed mode, OUT2 provides 3.3 V or 1.05 V, in

adjustable mode OUT2 can regulate an output between 0.7 V to 2.5 V by tracking an

external reference.

The switching frequencies of both switching controllers can be adjusted to 200 kHz/300 kHz,

400 kHz/300 kHz or 400 kHz/500 kHz respectively. To maximize the efficiency at light loads

a pulse skipping mode can be selected. Moreover a pulse skipping mode with a minimum

switching frequency of 33 kHz (non audible skip operation mode) can be selected to avoid

audible noise issue. The linear regulator can provide a fixed (5 V or 3.3 V) or an adjustable

output voltage. In order to reduce the power consumption the internal LDO can be turned off

and the LDO output can be supplied with an external voltage applied at LDO_SW pin

(switch-over function).

The PM6686 supplies two voltage references: 3.3 V and 2 V. The charge pump controller

can be programmed to regulate a 14 V output. The switching sections and the LDO have

independent enable signals. Moreover the switching sections have a selectable power up

sequence and a turn off management.

The device is protected against overvoltage, undervoltage and over temperature. Two

independent Power Good signals monitor the output voltage range of each switching

sections.

8.1

Switching sections

8.1.1

Output voltage set up

The switching sections can be configured in several ways.

OUT1 output voltage is configured with FB1 pin. If FB1 pin is tied to GND the PM6686

regulates 5 V while if FB1 is connected to VCC the controller set OUT1 at 1.5 V. Using an

external resistor divider the output can be adjusted following this equation:

Equation 1

⎟

⎠

⎞

⎜

⎝

⎛

⋅

OUT

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