peak

Vin

I

66 mA

80

=

+

W

skip

Vin

I

66 mA

160

£

+

W

(

)

min

max

max

ds

max

L

Vin

Vout

Iout

r (ON)

R

=

+

´

+

TPS62200, TPS62201, TPS62202, TPS62203

TPS62204, TPS62205, TPS62207, TPS62208

www.ti.com

SLVS417F – MARCH 2002 – REVISED JUNE 2015

Feature Description (continued)

7.3.3 Soft Start

The TPS6220x has an internal soft start circuit that limits the inrush current during start-up. This prevents

possible voltage drops of the input voltage in case a battery or a high-impedance power source is connected to

the input of the TPS6220x.

The soft start is implemented as a digital circuit increasing the switch current in steps of typically 60 mA, 120 mA,

240 mA, and then the typical switch current limit of 480 mA. Therefore the start-up time mainly depends on the

output capacitor and load current. Typical start-up time with a 10-µF output capacitor and 200-mA load current is

800 µs.

7.3.4 Low Dropout Operation 100% Duty Cycle

The TPS6220x offers a low input to output voltage difference, while still maintaining operation with the 100% duty

cycle mode. In this mode, the P-channel switch is constantly turned on. This is particularly useful in battery

powered applications to achieve longest operation time by taking full advantage of the whole battery voltage

range. The minimum input voltage to maintain regulation, depending on the load current and output voltage, can

be calculated as:

where

•

Ioutmax = maximum output current plus inductor ripple current.

•

rds(ON)max = maximum P-channel switch rds(ON).

•

RL = DC resistance of the inductor.

•

Voutmax = nominal output voltage plus maximum output voltage tolerance.

(1)

7.3.5 Enable

Pulling the enable low forces the part into shutdown, with a shutdown quiescent current of typically 0.1 µA. In this

mode, the P-channel switch and N-channel rectifier are turned off, the internal resistor feedback divider is

disconnected, and the whole device is in shutdown mode. If an output voltage, which could be an external

voltage source or super capacitor, is present during shutdown, the reverse leakage current is specified under

Electrical Characteristics. For proper operation the enable pin must be terminated and must not be left floating.

Pulling the enable high starts up the TPS6220x with the soft start as previously described.

7.4 Device Functional Modes

7.4.1 Power Save Mode Operation

As the load current decreases, the converter enters the power save mode operation. During power save mode,

the converter operates with reduced switching frequency in PFM mode and with a minimum quiescent current to

maintain high efficiency.

Two conditions allow the converter to enter the power save mode operation. One is when the converter detects

the discontinuous conduction mode. The other is when the peak switch current in the P-channel switch goes

below the skip current limit. The typical skip current limit can be calculated as

(2)

During the power save mode, the output voltage is monitored with the comparator by the thresholds comparator

low and comparator high. As the output voltage falls below the comparator low threshold set to typically 0.8%

above Vout nominal, the P-channel switch turns on. The P-channel switch is turned off as the peak switch

current is reached. The typical peak switch current can be calculated:

(3)

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