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Setting the Delay Times GDLY, EN delay

dly

5 A x td

5 A x td

C

=

=

Vref

1.23 V

m

m

(1)

dly

dly

5 A x 2.3 ms

C

=

= 9.3 nF

C

= 10 nF

1.23 V

m

Þ

(2)

Boost Converter

TPS65167

TPS65167A

SLVS760B – APRIL 2007 – REVISED OCTOBER 2007

Connecting an external capacitor to the GDLY and EN pin sets the delay time. To set the delay time, the external

capacitor is charged with a constant current source of typically 5

µA. The delay time is terminated when the

capacitor voltage has reached the threshold voltage of Vth = 1.230 V. The external delay capacitor is calculated:

Example for setting a delay time of 2.3 mS

The main boost converter operates in Pulse Width Modulation (PWM) and at a fixed switching frequency of 750

kHz The converter uses a unique fast response, voltage mode controller scheme with input voltage feedforward.

This achieves excellent line and load regulation (0.2% A load regulation typical) and allows the use of small

external components. To add higher flexibility to the selection of external component values the device uses

external loop compensation. Although the boost converter looks like a non-synchronous boost converter topology

operating in discontinuous conduction mode at light load, the device will maintain continuous conduction even at

light load currents. This is achieved with a novel architecture using an external Schottky diode with an integrated

MOSFET in parallel connected between SW and SUP. See the Functional Block Diagram. The intention of this

MOSFET is to allow the current to go below ground that occurs at light load conditions. For this purpose, a small

integrated P-Channel MOSFET with typically 10

external Schottky diode with the lower forward voltage will carry the current. This causes the converter to operate

with a fixed frequency in continuous conduction mode over the entire load current range. This avoids the ringing

on the switch pin as seen with standard non-synchronous boost converter, and allows a simpler compensation

for the boost converter.

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