PC Chips M571 (V7.0A) undocumented voltage settings - Part 2
------------------------------------------------------------
Here are the details of my core voltage calculations.
The following schematic diagram shows the relevant section of the
on-board power supply (reverse engineered):
6K04 9K53 20K0 Resistor
12K4 8K20 15K8 values
2V2 3V5 3V3 3V2 2V9 2V8 Jumper ID
From _____ _____
Load | \/ |14 R88 R89 R90 R91 R92 R93 Circuit ref
| | |--------|---|---|---|---|---|
| 1| |\Error | Vref |-| |-| |-| |-| |-| |-|
Vout |----|-| \_Amp | +5V | | | | | | | | | | | | Resistors
____|_| / | |-| |-| |-| |-| |-| |-|
V | 2| |/ | | | | | | |
| | | | O O O O O Jumpers
| | KA7500B | | O O O O O JP6
| |__________| | | | | | |
| |---|---|---|---|---|
|_______________________|
|
R79 |-|
10K2 | |
|-|
|
_|_
The Samsung KA7500B (=TL494) is a PWM regulator. The error amp senses
the output voltage and compares it with a setpoint derived from an
internal 5.0V reference and an external potential divider.
Various undocumented voltages can be obtained by:
(1) using multiple jumpers
(2) using a resistor in place of a jumper
(3) a combination of jumper and resistor
In the following diagram R1 represents one of R89,R90,R91,R92,R93.
R2 is the resistor that must be added to achieve a particular voltage.
+5V ref
___
|
|---|
| |
|-| |-|
12K4 | | | | R1
|-| |-|
| | ______
| O---| R2 |----|
| |----| | R = R1 + R2
| O-------------|
| |
|---|
|
|-|
10K2 | |
|-|
|
_|_
The following formulae determine values for V and R (=R1+R2).
5
Vout = ------------------
(volt) 12.4/10.2
1 + ----------
1 + 12.4/R
12.4
R (kohm) = ----------------
12.4/10.2
--------- - 1
5/V - 1
Example calculation:
--------------------
A CPU core voltage of 2.5V is desired. Allow for 0.07V voltage drop from
regulator to CPU (as in original design). Solving the second equation
for V=2.57 gives R = 43.4K ohm. We can approximate this resistance by
placing a 22K resistor in the 2V8 jumper position, ie 20K + 22K = 42K.
Solving the first equation for R=42 gives 2.58V, ie 2.51V at the CPU.
The following table lists the voltages that are available for the
various multiple jumper combinations (0=no jumper, 1=jumper installed).
Jumpers nominal V V - 0.07
3V5-2V8 (at regulator) (at CPU socket)
00000 2.26 2.19
OOOO1 2.86 2.79
OOO1O 2.97 2.9
OO1OO 3.27 3.2
OOO11 3.32 3.25
O1OOO 3.37 3.3
OO1O1 3.53 3.46
1OOOO 3.58 3.51
OO11O 3.59 3.52
O1OO1 3.6 3.53
O1O1O 3.65 3.58
OO111 3.76 3.69
1OOO1 3.76 3.69
O11OO 3.79 3.72
1OO1O 3.8 3.73
O1O11 3.82 3.75
1O1OO 3.91 3.84
O11O1 3.92 3.85
1OO11 3.93 3.86
O111O 3.95 3.88
11OOO 3.95 3.88
1O1O1 4.02 3.95
1O11O 4.04 3.97
11OO1 4.05 3.98
O1111 4.06 3.99
11O1O 4.07 4
1O111 4.13 4.06
111OO 4.14 4.07
11O11 4.15 4.08
111O1 4.21 4.14
1111O 4.23 4.16
11111 4.28 4.21
The following program was used to print the previous table. It may be
useful for analysing similar configurations on other boards.
FOR i = 1 TO &H1F
r = 1 / 12.4
jump$ = "OOOOO"
IF (i AND &H1) = &H1 THEN r = r + 1 / 6.04 : MID$(jump$, 1) = "1"
IF (i AND &H2) = &H2 THEN r = r + 1 / 8.2 : MID$(jump$, 2) = "1"
IF (i AND &H4) = &H4 THEN r = r + 1 / 9.53 : MID$(jump$, 3) = "1"
IF (i AND &H8) = &H8 THEN r = r + 1 / 15.8 : MID$(jump$, 4) = "1"
IF (i AND &H10) = &H10 THEN r = r + 1 / 20 : MID$(jump$, 5) = "1"
r = 1 / r
v = 5 / (r / 10.2 + 1)
v = CINT(v * 100) / 100
PRINT jump$, v, v - .07
NEXT i
This page was last modified on 17 July 2002