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an6069_01.0

November 2005 Application Note AN6069

Programmable Comparator Options

for the ispPAC-POWR1220AT8

Introduction

Lattice’s ispPAC

-POWR1220AT8 offers a wide range of features for managing multiple power supplies in a com-

plex system. This application note outlines the key features associated with the voltage monitoring functions. In

order to better understand the ﬂexible architecture of the front end, the circuitry will be broken down into sections to

be discussed individually. The relationships of these blocks is also discussed, along with how they interact with the

PLD and other functional blocks within the ispPAC-POWR1220AT8.

The ispPAC-POWR1220AT8 provides 24 independently programmable trip point comparators connected to 12 volt-

age monitoring pins. Each of the comparators has 368 programmable trip points, ranging from .664V to 5.734V. In

addition to these, there is a low level trip point for powered down supplies that trips at 75mV. The 75mV setting is

used to determine if a given supply has decayed all the way down and is safely off, before recycling it back on or

starting another sequence or event.

Differential Input Comparator

The ispPAC-POWR1220AT8 has 24 comparators, each independently programmable. Each set of VMON pins or

voltage monitors is tied to a pair of comparators (see Figure 1). The VMON pins themselves are a pair of differential

inputs to minimize measurement error in a noisy environment. The differential pair for each VMON, allows the

designer to monitor the voltage at a remote point on the board with a pair of pins, one the positive VMON and the

other the sense line or ground sense (VMONGS). Figure 1 below shows a simpliﬁed diagram of the ispPAC-

POWR1220AT8 controlling and monitoring a 1.5V supply. Note the remote sense line and location of the VMON1

voltage monitor line. The physical location on the net where the voltage is to be measured is critical if there is high

current for the supply rail or noise on the board. Each VMON has a ground sense line, these must be connected in

all cases. If the sense line is not hooked directly to the ground near the load, connect it to the local ground plane.

The ground sense lines can have a maximum voltage of -200mV to +300mV with respect to the ground of the isp-

PAC-POWR1220AT8.

Figure 1. Simpliﬁed Interface Showing VMON Groundsense

1.5V

Load

Side

Circuit

3.3V

VMON1

VMON1GS

ispPAC-POWR1220AT8

OUT5

VCCD

TRIM1

Resistor

Network

Trim

DC/DC

1.5V

Supply A

Programmable Comparator Options

Lattice Semiconductor for the ispPAC-POWR1220AT8

Trip Points

The 368 programmable trip points allow the user to select voltages around popular power supply ranges. The trip

points range from .664V (Table 1) to 5.734V (Table 2). In addition there is a low-level trip point at 75mV to deter-

mine if a power supply has discharged all the way down. Each VMON pin has the 368 programmable trip points

plus the 75mV trip point setting. To monitor supplies outside the range of these voltages such as 12V or 24V, a sim-

ple voltage divider can be placed in front of the VMON pins. See Lattice application note AN6041,

Extending the

VMON Input Range of ispPAC Power Manager Devices

for further information. The VMON input impedance, which

is typically 65k Ohms, must be considered when designing this voltage divider.

ispPAC-POWR12220AT8 Trip Point Tables

Table 1. Trip Points for Under-Voltage Detection

Fine

Range

Setting

Coarse Range Setting

123456789101112

1 0.786 0.936 1.114 1.326 1.571 1.874 2.232 2.650 3.139 3.738 4.792 5.703

2 0.782 0.930 1.108 1.319 1.563 1.864 2.220 2.636 3.123 3.718 4.766 5.674

3 0.778 0.926 1.102 1.312 1.554 1.854 2.209 2.622 3.106 3.698 4.741 5.643

4 0.773 0.921 1.096 1.305 1.546 1.844 2.197 2.607 3.089 3.678 4.715 5.612

5 0.769 0.916 1.090 1.298 1.537 1.834 2.185 2.593 3.072 3.657 4.689 5.581

6 0.765 0.911 1.084 1.290 1.529 1.825 2.173 2.579 3.056 3.637 4.663 5.550

7 0.761 0.906 1.078 1.283 1.520 1.815 2.161 2.565 3.039 3.618 4.638 5.520

8 0.756 0.901 1.072 1.276 1.512 1.805 2.149 2.550 3.022 3.598 4.612 5.489

9 0.752 0.896 1.066 1.269 1.503 1.795 2.137 2.536 3.005 3.578 4.586 5.459

10 0.748 0.891 1.060 1.262 1.495 1.785 2.125 2.522 2.988 3.558 4.561 5.428

11 0.744 0.886 1.054 1.255 1.486 1.774 2.113 2.507 2.971 3.537 4.535 5.397

12 0.739 0.881 1.048 1.248 1.478 1.764 2.101 2.493 2.954 3.517 4.509 5.366

13 0.735 0.876 1.042 1.240 1.470 1.754 2.089 2.479 2.937 3.497 4.483 5.336

14 0.731 0.871 1.036 1.233 1.461 1.744 2.077 2.465 2.920 3.477 4.457 5.305

15 0.727 0.866 1.030 1.226 1.453 1.734 2.064 2.450 2.903 3.457 4.431 5.274

16 0.723 0.861 1.024 1.219 1.444 1.724 2.052 2.436 2.886 3.437 4.406 5.244

17 0.718 0.856 1.018 1.212 1.436 1.714 2.040 2.422 2.869 3.416 4.380 5.213

18 0.714 0.851 1.012 1.205 1.427 1.704 2.028 2.407 2.852 3.396 4.355 5.183

19 0.710 0.846 1.006 1.198 1.419 1.694 2.016 2.393 2.836 3.376 4.329 5.152

20 0.706 0.841 1.000 1.190 1.410 1.684 2.004 2.379 2.819 3.356 4.303 5.121

21 0.701 0.836 0.994 1.183 1.402 1.673 1.992 2.365 2.802 3.336 4.277 5.090

22 0.697 0.831 0.988 1.176 1.393 1.663 1.980 2.350 2.785 3.316 4.251 5.059

23 0.693 0.826 0.982 1.169 1.385 1.653 1.968 2.337 2.768 3.296 4.225 5.030

24 0.689 0.821 0.976 1.162 1.376 1.643 1.956 2.323 2.752 3.276 4.199 4.999

25 0.684 0.816 0.970 1.155 1.369 1.633 1.944 2.309 2.735 3.256 4.174 4.968

26 0.680 0.810 0.964 1.148 1.361 1.623 1.932 2.294 2.718 3.236 4.149 4.937

27 0.676 0.805 0.958 1.140 1.352 1.613 1.920 2.280 2.701 3.216 4.123 4.906

28 0.672 0.800 0.952 1.133 1.344 1.603 1.908 2.266 2.684 3.196 4.097 4.876

29 0.668 0.795 0.946 1.126 1.335 1.593 1.896 2.251 2.667 3.176 4.071 4.845

30 0.664 0.790 0.940 1.119 — 1.583 1.884 2.236 — 3.156 4.045 4.815

Low-V

Sense

75mV