Datasheet

TPS53315

www.ti.com

SLUSAE6 –DECEMBER 2010

General Description

The TPS53315 is a high-efficiency, single channel, synchronous buck converter suitable for low output voltage

point-of-load applications in computing and similar digital consumer applications. The device features proprietary

D-CAP™ mode control combined with an adaptive on-time architecture. This combination is ideal for building

modern low duty ratio, ultra-fast load step response DC-DC converters. The output voltage ranges from 0.6 V to

5.5 V. The conversion input voltage range is from 3 V up to 15 V. The D-CAP™ mode uses the ESR of the

output capacitor(s) to sense the device current. One advantage of this control scheme is that it does not require

an external phase compensation network. This allows a simple design with a low external component count.

Eight preset switching frequency values can be chosen using a resistor connected from the RF pin to ground or

the VREG pin. Adaptive on-time control tracks the preset switching frequency over a wide input and output

voltage range while allowing the switching frequency to increase at the step-up of the load.

The TPS53315 has a MODE pin to select between auto-skip mode and forced continuous conduction mode

(FCCM) for light load conditions. The MODE pin also sets the selectable soft-start time ranging from 0.7 ms to

5.6 ms.

Enable and Soft Start

When the EN pin voltage rises above the enable threshold voltage (typically 1.2 V), the controller enters its

start-up sequence. The internal LDO regulator starts immediately and regulates to 5 V at the VREG pin. The

controller then uses the first 250 ms to calibrate the switching frequency setting resistance attached to the RF pin

and stores the switching frequency code in internal registers. However, switching is inhibited during this phase. In

the second phase, an internal DAC starts ramping up the reference voltage from 0 V to 0.6 V. Depending on the

MODE pin setting, the ramping up time varies from 0.7 ms to 5.6 ms. Smooth and constant ramp-up of the

output voltage is maintained during start-up regardless of load current.

Table 1. Soft-Start and MODE

SOFT-START TIME R

MODE

MODE SELECTION ACTION

(ms) (kΩ)

0.7 39

1.4 100

Auto Skip Pull down to GND

2.8 200

5.6 475

0.7 39

1.4 100

Forced CCM

(1)

Connect to PGOOD

2.8 200

5.6 475

(1) The device transitions into FCCM after the PGOOD pin goes high.

Product Folder Link(s): TPS53315