Margin Up/Down Controls

R

U or RD +

499

D %

* 99.8 kW

(2)

C

O

+

C

I

V

I

GND

MarginDown

L

O

A

D

Q2

+V

O

+V

O

Q1

+

MarginUp

0V

R

D

R

U

PT H12010W

(TopView)

1

2

10 9

8

7

6

5

4

3

GND

R

0.1W,1%

SET

PTH12020W/L

www.ti.com ............................................................................................................................................................. SLTS208I – MAY 2003 – REVISED MARCH 2009

The PTH12060, PTH12010, PTH12020, and PTH12030 products incorporate Margin Up and Margin Down

control inputs. These controls allow the output voltage to be momentarily adjusted [1], either up or down, by a

nominal 5%. This provides a convenient method for dynamically testing the operation of the load circuit over its

supply margin or range. It can also be used to verify the function of supply voltage supervisors. The ±5% change

is applied to the adjusted output voltage, as set by the external resistor, RSET at the VO Adjust pin.

The 5% adjustment is made by pulling the appropriate margin control input directly to the GND terminal [2]. A

low-leakage, open-drain device, such as an n-channel MOSFET or p-channel JFET is recommended for this

purpose [3]. Adjustments of less than 5% can also be accommodated by adding series resistors to the control

inputs. The value of the resistor can be selected from Table 6, or calculated using Equation 2.

Margin Up/Down Adjust Resistance Calculation

To reduce the margin adjustment to a value less than 5%, series resistors are required (See RD and RU in

Figure 19). For the same amount of adjustment, the resistor value calculated for RU and RD is the same. The

formula is as follows.

Where

Δ% = The desired amount of margin adjust in percent.

Notes:

1. The Margin Up and Margin Down controls were not intended to be activated simultaneously. If they are

activated simultaneously, the affect on the output voltage may not completely cancel, resulting in the

possibility of a slightly higher error in the output voltage set point.

2. The ground reference should be a direct connection to the module GND. This produces a more accurate

adjustment at the load circuit terminals. The transistors Q1 and Q2 should be located close to the regulator.

3. The Margin Up and Margin Down control inputs are not compatible with devices that source voltage. This

includes TTL logic. These are analog inputs and should only be controlled with a true open-drain device

(preferably a discrete MOSFET transistor). The device selected should have low off-state leakage current.

Each input sources 8 µA when grounded, and has an open-circuit voltage of 0.8 V.

Table 6. Margin Up/Down Resistor Values

PERCENTAGE ADJUST (%)

5

4

3

2

1

RU / RD(kΩ)

0.0

24.9

66.5

150.0

397.0

Figure 19. Margin Up/Down Application Schematic

Copyright © 2003–2009, Texas Instruments Incorporated

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