MAX1717 查看數據表（PDF） - Maxim Integrated
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MAX1717 Datasheet PDF : 33 Pages
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Dynamically Adjustable, Synchronous
Step-Down Controller for Notebook CPUs
A/B Internal Mux
The MAX1717 contains an internal mux that can be used
to select one of two programmed DAC codes and output
voltages. The internal mux is controlled with the A/B pin,
which selects between the A mode and the B mode. In
the A mode, the voltage levels on D0–D4 select the out-
put voltage according to Table 4. Do not leave D0–D4
floating; there are no internal pull-up resistors.
The B mode is programmed by external resistors in
series with D0–D4, using a unique scheme that allows
two sets of data bits using only one set of pins (Figure
7). When A/B goes low (or during power-up with A/B
low), D0–D4 are tested to see if there is a large resis-
tance in series with the pin. If the voltage level on the
pin is a logic low, an internal switch connects the pin to
an internal 40kΩ pull-up for about 4µs to see if the pin
voltage can be forced high (Figure 8). If the pin voltage
cannot be pulled to a logic high, the pin is considered
low impedance and its B-mode logic state is low. If the
pin can be pulled to a logic high, the impedance is
considered high and so is the B-mode logic state.
Similarly, if the voltage level on the pin is a logic high,
an internal switch connects the pin to an internal 8kΩ
pull-down to see if the pin voltage can be forced low. If
so, the pin is high-impedance and its B-mode logic
state is high. Otherwise, its logic state is low.
A high pin impedance (and logic high) is 100kΩ or
greater, and a low impedance (and logic low) is 1kΩ or
less. The Electrical Characteristics guaranteed levels for
these impedances are 95kΩ and 1.05kΩ to allow the use
of standard 100kΩ and 1kΩ resistors with 5% tolerance.
If the output voltage codes are fixed at PC board
design time, program both codes with a simple combi-
nation of pin-strap connections and series resistors
(Figure 7). If the output voltage codes are chosen dur-
ing PC board assembly, both codes can be indepen-
dently programmed with resistors (Figure 9). This
matrix of 10 resistor-footprints can be programmed to all
possible A-mode and B-mode code combinations with
only five resistors.
Often, one or more output-voltage codes are provided
directly by the CPU’s VID pins. If the CPU actively dri-
ves these pins, connect A/B high (A mode) and let the
CPU determine the output voltages. If the B mode is
needed for startup or other reasons, insert resistors in
series with D0–D4 to program the B-mode voltage. Be
sure that the VID pins are actively driven at all times.
If the CPU’s VID pins float, the open-circuit pins can
present a problem for the MAX1717’s internal mux. The
Table 4. Output Voltage vs. DAC Codes
D4
D3
D2
D1
D0
VOUT (V)
0
0
0
0
0
2.00
0
0
0
0
1
1.95
0
0
0
1
0
1.90
0
0
0
1
1
1.85
0
0
1
0
0
1.80
0
0
1
0
1
1.75
0
0
1
1
0
1.70
0
0
1
1
1
1.65
0
1
0
0
0
1.60
0
1
0
0
1
1.55
0
1
0
1
0
1.50
0
1
0
1
1
1.45
0
1
1
0
0
1.40
0
1
1
0
1
1.35
0
1
1
1
0
1.30
0
1
1
1
1
No CPU
1
0
0
0
0
1.275
1
0
0
0
1
1.250
1
0
0
1
0
1.225
1
0
0
1
1
1.200
1
0
1
0
0
1.175
1
0
1
0
1
1.150
1
0
1
1
0
1.125
1
0
1
1
1
1.100
1
1
0
0
0
1.075
1
1
0
0
1
1.050
1
1
0
1
0
1.025
1
1
0
1
1
1.000
1
1
1
0
0
0.975
1
1
1
0
1
0.950
1
1
1
1
0
0.925
1
1
1
1
1
No CPU
Note: In the no-CPU state, DH and DL are held low and the
slew-rate controller is set for 0.9V.
processor’s VID pins can be used for the A-mode set-
ting, together with suitable pull-up resistors. However,
the B-mode VID code is set with resistors in series with
D0–D4, and in order for the B-mode to work, any pins
intended to be B-mode logic low must appear to be low
impedance, at least for the 4µs sampling interval.
20 ______________________________________________________________________________________
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