TPS65281, TPS65281-1

SLVSBH7B – JULY 2012 – REVISED DECEMBER 2012

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TERMINAL FUNCTIONS

NAME

NO.

DESCRIPTION

SS

1

Soft-start and tracking input for buck converter. An internal 5-µA current source is connected to this pin. An

external soft-start can be programmed by connecting a capacitor between this pin and ground. Leave the pin

floating to have a default 1-ms of soft-start time. This pin allows the start-up of buck output to track an

external voltage using an external resistor divider at this pin.

COMP

2

Error amplifier output and Loop compensation pin for buck. Connect a series RC to compensate the control

loop of buck converter.

ROSC

3

Oscillator clock frequency control pin. Connect the pin to ground for a fixed 300-kHz switching frequency.

Connect the pin to V7V or float the pin for a fixed 600-kHz switching frequency. Other switch frequencies

between 300 kHz to 1.4 MHz can be programmed using a resistor connected from this pin to ground. A

internal 10-µA pull-up current develops a voltage to be used in oscillator. Directly applying the voltage to the

ROSC pin can linearly adjust the switching frequency.

RLIM

4

Power switch current limit control pin. An external resistor used to set current limit threshold of power switch.

Recommended 15 k

Ω ≤ RLIM ≤ 232 kΩ.

EN_SW

5

Enable pin of power switch. Logic high turns on power switch. Forcing the pin below 0.4 V shuts down power

switch. Not recommend floating this pin, though there is a 2.5-M

Ω pull-up resistor connecting this pin.

nFAULT

6

Active low open drain output, asserted in conditions when over-current happens for more than 10 ms or

reverse-voltage of power switch for more than 4 ms.

AGND

7

Analog ground common to buck controller and power switch controller. It must be routed separately from

high current power grounds to the (-) terminal of bypass capacitor of internal V7V LDO output.

SW_OUT

8

Power switch output pin

SW_IN

9

Power switch input pin

FB

10

Feedback sensing pin for buck output voltage. Connect this pin to the resistor divider of buck output. The

feedback reference voltage is 0.8 V±1%.

LX

11

Switching node connection to the internal power FETs, inductor and bootstrap capacitor for buck converter.

BST

12

Bootstrapped supply to the high side floating gate driver in buck converter. Connect a capacitor (recommend

47 nF) from BST pin to LX pin.

PGND

13

Power ground connection. Connect PGND pin as close as practical to the (-) terminal of input ceramic

capacitor.

VIN

14

Input power supply for buck. Connect VIN pin as close as practical to the (+) terminal of a input ceramic

capacitor (suggest 10 µF).

V7V

15

Internal LDO output. The internal gate driver for low side power MOSFET and control cirduits are powered

from this voltage. Decouple this pin to power ground with a minimum 1-µF ceramic capacitor. The output

voltage level of LDO is regulated to typical 6.3 V for optimal conduction on-resistances of internal power

MOSFETs.

EN

16

Enable for buck converter and the device. Logic high enables buck converter and bias supply to power

switches. Forcing the pin below 0.4 V shuts down the entire device, reducing the quiescent current to

approximate typical 7 µA. Not recommend floating this pin. The device can be automatically started up with

connecting EN pin to VIN though a 10 k

Ω resistor.

Power PAD

Exposed pad beneath the IC. Connect to the ground. Always solder power pad to the board, and have as

many thermal vias as possible on the PCB to enhance power dissipation. There is no ground or any other

electric signal downbonded to the pad inside the IC package.

6

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Product Folder Links: TPS65281 TPS65281-1