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Application Notes

Operating Features of the Programmable

PT6700 “Excalibur™” Series ISRs

Power Good

Programmable versions of the PT6700 Series regulators

incorporate a PWR Good output (pin 2). This output is

open-drain and generates an acitve-high signal when the

sensed output from the ISR is within a nominal ±10% of

the programmed set point. When the regulated output is

outside this range, pin 2 asserts a logic low (typically <0.1V). A

10-k

Ω pull-up resistor to a valid bus voltage is required.

If the power good feature is not used, the pull-up resistor

can be omitted. The maximum voltage that may be ap-

plied to the pull-up resistor is 15V.

Over-Voltage Protection (OVP)

The PT6700 programmable regulators also incorporate

an OVP function. The OVP DRV (pin 1) normally has a

logic low output (typically <0.1V). When the ISR’s sensed

output exceeds the programmed output setting by 15%,

pin 1 produces a 60mA, +12V drive signal. This drive

signal can trigger an SCR, which can be used to disable

the input voltage (via a fuse), or alternatively interface to

another external monitoring device. When the ISR output

voltage returns to within 15% of its programmed setting,

pin 1 reverts back to its low state. If the OVP function is

not used, pin 1 may be left open circuit.

Stand-By Function

The PT6700 series ISRs incorporate a standby function.

This feature may be used for power-up sequencing, or

wherever there is a requirement for the output voltage

to be controlled by external circuitry.

If the STBY* input (pin 8) is left open-circuit the regulator

operates normally, providing a regulated output when a

current to typically 20mA (30mA max). Applying a ground

signal to pin 8 prior to power-up, will disable the output

during the period that input power is applied. To ensure

that the regulator output is properly enabled, pin 8 must

be open circuit.

Parameter

Min

Typ

Max

Enable

Disable

-0.1V

0.4V

1.0V

10µA

Figure 1

Figure 2

C

out

+

C

in

+

5V

COM

Inhibit

L

O

A

D

V

o

=2.5V

COM

Q1

BSS138

PT6700

76

543

2 3

19-22

13

8

14-18

2

10-12

Vo

Vin

GND

SNS(+)

SNS(-)

Pwr

Good

STBY

VID4 - VID0

1

OVP

R1

10k

OVP DRV

Pwr

Good

PT6701/6702/6703, & PT6721/6722

0

5

10

15

20

25

30

35

40

t (milli - secs)

Notes:

1. The standby on a PT6700 series regulator must be controlled

with an open-drain low-leakage (<100nA) MOSFET (See

fig. 1). Table 1 gives the threshold requirements. Do Not use a

pull-up resistor. The control input has an open-circuitvoltageof

between 4Vdc and 5Vdc. To set the regulator output to zero,

the control pin must be “pulled” to less than 1.0Vdc by sinking

current to ground.

2. When placed in the standby mode, the regulator output may

assert a low impedance to ground. If an external voltage is

applied to the output, it will sink current and possibly over-

stress the part.

Turn-On Time

at pin 8. After a 10-15ms delay the regulator output

rises and reaches full output voltage within 30ms. Fig. 2

shows the typical waveforms of a PT6701 following the

age was set to 2.5V, and the waveforms were measured

with a 5V input source, and 10A resistive load.