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Overvoltage Protection

Input Capacitor Selection VINB, SUP, SUPN, AVIN, Inductor Input Terminal

Boost Converter Design Procedure

1. Converter Duty Cycle:

D + 1 *

Vin

h

Vout

2. Maximum output current:

Iout + Isw *

Vin

D

2

ƒs

L

(1 * D)

3. Peak switch current:

I

Vin

D

2

ƒs

L

)

1 * D

TPS65167

TPS65167A

SLVS760B – APRIL 2007 – REVISED OCTOBER 2007

With:

The main boost converter has an overvoltage protection of the main switch M1 if the feedback pin (FB) is floating

or shorted to GND causing the output voltage to rise. In such an event, the output voltage is monitored with the

overvoltage protection comparator on the SUP pin. As soon as the comparator trips at typically at 20 V then the

boost converter stops switching. The output voltage will fall below the overvoltage threshold and the converter

continues to operate. See Figure 4.

Note: During high voltage stress test the overvoltage protection is disabled.

For good input voltage filtering, low ESR ceramic capacitors are recommended. The TPS65167 has an analog

input AVIN as well as a power supply input SUP powering all the internal rails. A 1-

µF bypass capacitor is

required as close as possible from AVIN to GND as well as from SUP to GND. The SUPN pin needs to be

bypassed with a 470-nF capacitor. Depending on the overall load current two or three 22-

µF input capacitors are

required. For better input voltage filtering, the input capacitor values can be increased. To reduce the power

losses across the external isolation switch a filter capacitance at the input terminal of the inductor is required. To

minimize possible audible noise problems, two 10-

µF capacitors in parallel are recommended. More capacitance

will further reduce the ripple current across the isolation switch. See Table 2 and the typical applications for input

capacitor recommendations.

Table 2. Input Capacitor Selection

CAPACITOR

COMPONENT SUPPLIER

COMMENTS

22

µF/16 V

Taiyo Yuden EMK316BJ226ML

Pin VINB

2

×10 µF/25 V

Taiyo Yuden TMK316BJ106KL

Pin VINB (alternative)

2

×10 µF/25 V

Taiyo Yuden TMK316BJ106KL

Inductor input terminal

1

µF/35 V

Taiyo Yuden GMK107BJ105KA

Pin SUP

1

µF/25 V

Taiyo Yuden TMK107BJ105KA

Pin AVIN

470 nF/25 V

Taiyo Yuden TMK107BJ474MA

Pin SUPN

x

The first step in the design procedure is to verify whether the maximum possible output current of the boost

converter supports the specific application requirements. To simplify the calculation, the fastest approach is to

estimate the converter efficiency by taking the efficiency numbers from the provided efficiency curves or to use a

worst case assumption for the expected efficiency, e.g., 80%. With the efficiency number it is possible to

calculate the steady state values of the application.

With Isw = converter switch current (minimum switch current limit = 3.5 A)

fs = converter switching frequency (typical 750 kHz)

L = Selected inductor value

η = Estimated converter efficiency (use the number from the efficiency curves or 0.8 as an estimation)

18

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