0

100

200

300

400

500

600

700

800

900

0

0.5

1

1.5

2

2.5

3

f

- Switching Frequency - MHz

sw

R

k

f

OSC

SW

(

) = 239.13

W

·

-1.149

TPS65270

www.ti.com

SLVSAX7C – AUGUST 2011 – REVISED APRIL 2012

OVERVIEW

TPS65270 is a power management IC with two step-down buck converters. Both high-side and low-side

MOSFETs are integrated to provide fully synchronous conversion with higher efficiency. TPS65270 can support

4.5-V to 18-V input supply, 2-A continuous current for Buck 1 and 3 A for Buck 2. The buck converters have an

automatic PSM mode, which can improve power dissipation during light loads. Alternatively, the device

implements a constant frequency mode by connecting the LOW_P pin to ground. The wide switching frequency

of 300 kHz to 1.4 MHz allows for efficiency and size optimization. The switching frequency is adjustable by

selecting a resistor to ground on the ROSC pin. Input ripple is reduced by 180° out-of-phase operation between

Buck 1 and Buck 2.

Both buck converters have peak current mode control which simplifies the loop compensation. A traditional type

II compensation network can stabilize the system and achieve fast transient response. Moreover, an optional

capacitor in parallel with the upper resistor of the feedback divider provides one more zero and makes the

crossover frequency over 100 kHz. Each buck converter has an individual cycle-by-cycle current limit and low

side reverse current limit.

The device has a built-in LDO regulator. During a standby mode, the 6.5-V LDO can be used to drive MCU and

other active loads. with this LDO, system is able to turn off the two buck converters so as to reduce the power

consumption and improve the standby efficiency. Each converter has its own programmable soft start that can

reduce the input inrush current. The individual Enable pins for each independent control of each output voltage

and power sequence.

DETAILED DESCRIPTION

Adjustable Switching Frequency

To select the internal switching frequency connect a resistor from ROSC to ground. Figure 14 shows the required

resistance for a given switching frequency.

Figure 14. ROSC vs Switching Frequency

(1)

For operation at 800 kHz, a 300-k

Ω resistor is required.

Out-of-Phase Operation

In order to reduce input ripple current, Buck 1 and Buck 2 operate 180° out-of-phase. This enables the system

having less input ripple, then to lower component cost, save board space and reduce EMI.

Delayed Start-Up

If a delayed start-up is required on any of the buck converters fit a ceramic capacitor to the ENx pins. The delay

added is ~0.75 ms per nF connected to the pin. Note that the EN pins have a weak 1-M

Ω pull-up to the 5-V rail.

Copyright © 2011–2012, Texas Instruments Incorporated

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Product Folder Link(s): TPS65270