MAX1711 Maxim, MAX1711 Datasheet - Page 12

• Manufacturer Part Number: MAX1711
• Description: High-Speed / Digitally Adjusted Step-Down Controllers for Notebook CPUs
• Manufacturer: Maxim

High-Speed, Digitally Adjusted
Step-Down Controllers for Notebook CPUs
Table 1. MAX1710 FB Output Voltage
DAC Codes
low-side switch current is below the current-limit thresh-
old, and the minimum off-time one-shot has timed out.
The heart of the PWM core is the one-shot that sets the
high-side switch on-time. This fast, low-jitter, adjustable
one-shot includes circuitry that varies the on-time in
response to battery and output voltage. The high-side
switch on-time is inversely proportional to the battery
voltage as measured by the V+ input, and directly pro-
portional to the output voltage as set by the DAC code.
This algorithm results in a nearly constant switching fre-
quency despite the lack of a fixed-frequency clock gen-
erator. The benefits of a constant switching frequency
are twofold: first, the frequency can be selected to avoid
noise-sensitive regions such as the 455kHz IF band;
second, the inductor ripple-current operating point
remains relatively constant, resulting in easy design
methodology and predictable output voltage ripple.
where K is set by the TON pin-strap connection and
0.075V is an approximation to accommodate for the
expected drop across the low-side MOSFET switch.
One-shot timing error increases for the shorter on-time
12
D3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
______________________________________________________________________________________
On-Time = K (V
D2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
D1
On-Time One-Shot (TON)
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
OUT
+ 0.075V) / V
D0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
VOLTAGE (V)
IN
OUTPUT
2.00
1.95
1.90
1.85
1.80
1.75
1.70
1.65
1.60
1.55
1.50
1.45
1.40
1.35
1.30
1.25
settings due to fixed propagation delays and is approxi-
mately ±12.5% at 550kHz and 400kHz, and ±10% at the
two slower settings. This translates to reduced switch-
ing-frequency accuracy at higher frequencies. (see
Table 5). Switching frequency increases as a function of
load current due to the increasing drop across the low-
Table 2. MAX1711 FB Output Voltage
DAC Codes
* See Table 3
D4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
D3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
D2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
D1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
D0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
VOLTAGE (V)
Shutdown 3*
Shutdown 3*
OUTPUT
1.275
1.250
1.225
1.200
1.175
1.150
1.125
1.100
1.075
1.050
1.025
1.000
0.975
0.950
0.925
2.00
1.95
1.90
1.85
1.80
1.75
1.70
1.65
1.60
1.55
1.50
1.45
1.40
1.35
1.30