Tr i p ath Technol ogy, I n c. - Techni cal In fo rma t io n

24

TK2150 – Rev. 1.0/12.02

Using the resistor values from above, the actual minimum over voltage turn off points will be:

RN_OFF)

(MIN_OV_TU

VPPSENSE

VPP1

N_OFF

MIN_OV_TUR

I

R

VPP

×

=

)

I

R

(

VNN

RN_OFF)

(MIN_OV_TU

VNNSENSE

VNN1

N_OFF

MIN_OV_TUR

×

−

=

The other three trip points can be calculated using the same formula but inserting the appropriate

between the minimum overvoltage turn off and maximum under voltage turn-off for both the VPP

and VNN supplies.

N_OFF

MAX_UV_TUR

N_OFF

MIN_OV_TUR

RANGE

VPP

-

VPP

VPP

=

N_OFF

MAX_UV_TUR

N_OFF

MIN_OV_TUR

RANGE

VNN

-

VNN

VNN

=

VN10 Supply and Switch Mode Power Supply Controller

VN10 is an additional supply voltage required by the TP2150. VN10 must be 10 volts more

positive than the nominal VNN. VN10 must track VNN. Generating the VN10 supply requires

some care.

The proper way to generate the voltage for VN10 is to use a 10V-postive supply voltage

referenced to the VNN supply. The TP2150 has an internal switch mode power supply

controller which generates the necessary floating power supply for the MOSFET driver stage

in the TP2150 (nominally 10V with the external components shown in Application / Test

Circuit). The SMPSO pin (pin 60) provides a switching output waveform to drive the gate of a

P channel MOSFET. The source of the P channel MOSFET should be tied to power ground

and the drain of the MOSFET should be tied to the VN10 through a 100uH inductor. The

performance curves shown in this datasheet as well as the efficiency measurements were

done using the internal VN10 generator. Tripath recommends using the internal VN10

generator to power the TP2150. Figure 6 shows how the VN10 generator should be

connected.

Q

P

+

VNN

VN10

VNN

C

SW

0.1uF

C

SW

100uF

L

SW

100uH

D

SW

B1100DICT

59

60

R

R

C

SW FB

0.1uF

SW-FB

SMPSO

VN10

Switchmode

Power Supply

TP2150

Figure 6: VN10 Generator

In some cases, though, a designer may wish to use an external VN10 generator.

The

specification for VN10 quiescent current (200mA typical, 250mA maximum) in the Electrical

Characteristics section states the amount of current needed when an external floating supply is

used. If the internal VN10 generator is not used, Tripath recommends shorting SMPSO(pin 60) to

VNN(pin 42) and SW-FB(pin 59) to VNN(pin 42).

One apparent method to generate the VN10 supply voltage is to use a negative IC regulator to

drop PGND down to 10V (relative to VNN). This method will not work since negative regulators