R1

R4

R3 =

1 +

x

R4

R2

1.56

æ

ö

-

ç

÷

è

ø

1.25V

R4 =

300 A

1

R3

R1

1

=

1 +

x

R4

R2

1.56

æ

ö

+

ç

÷

è

ø

TLV62090

www.ti.com

SLVSBB9D – MARCH 2012 – REVISED SEPTEMBER 2015

Feature Description (continued)

In Figure 6, the output V2 will track the voltage applied to V1. Simultaneous voltage tracking is possible for

output voltages of V2

≥1.25 V. The voltage will track simultaneously when following conditions are met:

(3)

As the fraction of R3/R4 becomes larger the voltage V1 will ramp up faster than V2. If it gets smaller, then the

ramp will be slower than V2. R4 needs to be determined first using Equation 4.

(4)

In the calculation of R4, 300 µA current is used to achieve sufficient accuracy by taking into account the typical

7.5 µA soft-start current. For simultaneous tracking R3 is calculated using Equation 5.

(5)

8.3.3 Short Circuit Protection (Hiccup-Mode)

The device is protected against hard short circuits to GND and over-current events. This is implemented by a two

level short circuit protection. During start-up and when the output is shorted to GND the switch current limit is

reduced to 1/3 of its typical current limit of 4.6 A. Once the output voltage exceeds typically 0.6 V the current limit

is released to its nominal value. The full current limit is implemented as a hiccup current limit. Once the internal

current limits is triggered 32 times the device stops switching and starts a new start-up sequence after a typical

delay time of 66 µS passed by. The device will go through these cycles until the high current condition is

released.

8.3.4 Output Discharge Function

To make sure the device starts up under defined conditions, the output gets discharged via the VOS pin with a

typical discharge resistor of 200

Ω whenever the device shuts down. This happens when the device is disabled

or if thermal shutdown, undervoltage lockout or short circuit hiccup-mode is triggered.

8.3.5 Power Good Output (PG)

The power good output is low when the output voltage is below its nominal value. The power good will become

high impedance once the output is within 5% of regulation. The PG pin is an open drain output and is specified to

typically sink up to 1 mA. This output requires a pull-up resistor to be monitored properly. The pull-up resistor

cannot be connected to any voltage higher than the input voltage of the device.

8.3.6 Undervoltage Lockout (UVLO)

To avoid mis-operation of the device at low input voltages, an undervoltage lockout is included. UVLO shuts

down the device at input voltages lower than typically 2.2 V with a 200 mV hysteresis.

8.3.7 Thermal Shutdown

The device goes into thermal shutdown once the junction temperature exceeds typically 150°C with a 20°C

hysteresis.

8.4 Device Functional Modes

8.4.1 PWM Operation

At medium to heavy load currents, the device operates with pulse width modulation (PWM) at a nominal

switching frequency of 1.4 MHz. As the load current decreases, the converter enters the Power Save Mode

operation reducing its switching frequency. The device enters Power Save Mode at the boundary to

discontinuous conduction mode (DCM).

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