Datasheet

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m c m

B = 2 1 + m = 2 +

´ ¦ ´ ´ D¦ ¦

TPS82670, TPS82671, TPS82672, TPS82673, TPS82674

TPS82675, TPS82676, TPS82677, TPS826711, TPS826745, TPS826765

www.ti.com

SLVSAI0F –OCTOBER 2010–REVISED NOVEMBER 2012

The maximum switching frequency is limited by the process and by the parameter modulation ratio (δ), together

with f

, which is the bandwidth of the side-band harmonics around the carrier frequency f

. The bandwidth of a

frequency modulated waveform is approximately given by the Carson’s rule and can be summarized as:

(3)

< RBW: The receiver is not able to distinguish individual side-band harmonics; so, several harmonics are

added in the input filter and the measured value is higher than expected in theoretical calculations.

> RBW: The receiver is able to properly measure each individual side-band harmonic separately, so that the

measurements match the theoretical calculations.

SOFT START

The TPS8267x has an internal soft-start circuit that limits the in-rush current during start-up. This circuit limits

input voltage drop when a battery or a high-impedance power source is connected to the input of the MicroSiP™

DC/DC converter.

The soft-start system progressively increases the switching on-time from a minimum pulse-width of 35ns as a

function of the output voltage. This mode of operation continues for approximately 100μs after the enable. If the

output voltage does not reach its target value within the soft-start time, the soft-start transitions to a second mode

of operation.

If the output voltage rises above approximately 0.5V, the converter increases the input current limit and thus

enables the power supply to come up properly. The start-up time mainly depends on the capacitance present at

the output node and the load current.

ENABLE

The TPS8267x device starts operation when EN is set high and starts up with the soft start as previously

described. For proper operation, the EN pin must be terminated and must not be left floating.

Pulling the EN pin low forces the device into shutdown. In this mode, all internal circuits are turned off and the

current reduces to the device leakage current, which is typically a few hundred nanoamps.

The TPS8267x device can actively discharge the output capacitor when it turns off. The integrated discharge

resistor has a typical resistance of 100 Ω. The required time to ramp down the output voltage depends on the

load current and the capacitance present at the output node.

Product Folder Links: TPS82670 TPS82671 TPS82672 TPS82673 TPS82674 TPS82675 TPS82676 TPS82677

TPS826711 TPS826745 TPS826765