MAX1809ETI+T Maxim Integrated Products, MAX1809ETI+T Datasheet - Page 9

• Manufacturer Part Number: MAX1809ETI+T
• Description: IC DDR TERMINATION 28-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1809ETI+T

• Applications: Converter, DDR
• Voltage - Input: 3 ~ 5.5 V
• Number Of Outputs: 1
• Voltage - Output: 1.1 ~ 5.5 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX1809 features a programmable PWM-mode
switching frequency, which is set by the input and out-
put voltage and the value of R
TOFF to GND. R
time in PWM mode. Use the following equation to select
the off-time while sourcing current according to the
desired switching frequency in PWM mode:
where:
Figure 3. Sourcing and Sinking Capabilities of the MAX1809
Programming the Switching Frequency
t
V
V
OFF
IN
OUT
= the input voltage
t
3A, 1MHz, DDR Memory Termination Supply
= the programmed off-time
OFF
= the output voltage
SYNCHRONOUS BOOST MODE
SYNCHRONOUS BUCK MODE
=
TOFF
(SOURCING CURRENT)
f
SW IN
(SINKING CURRENT)
_______________________________________________________________________________________
(
V
(
V
and Off-Time and On-Time
IN
sets the PMOS power switch off-
V
IN
−
−
V
V
OUT
PMOS
V
I
IN
SOURCE
I
SINK
−
TOFF
V
+
PMOS
V
NMOS
, connected from
)
V
V
OUT
SOURCE
)
> V
OUT
Make sure that t
when sourcing current. Select R
formula:
Recommended values for R
430kΩ for off-times of 0.4µs to 4µs.
When sinking current, the switching frequency increas-
es due to the on-resistances of the internal switches
adding to the voltage across the inductor, reducing the
on-time. Calculate t
equation:
Check that t
than 350ns.
The key inductor parameters must be specified: inductor
value (L) and peak current (I
tion includes a constant, denoted as LIR, which is the
ratio of peak-to-peak inductor AC current (ripple current)
Figure 4. Maximum Recommended Operating Frequency vs.
Input Voltage
V
PMOS power switch
V
NMOS synchronous-rectifier switch
R
f
SW
R
PMOS
NMOS
NMOS
TOFF
= switching frequency
1400
1200
1000
800
600
400
200
t
ON
ON
0
|
= (t
2.7
= the voltage drop across the internal
= the voltage drop across the internal
=
in the current sinking mode is greater
OFF
ON
t
OFF
3.1
ON
and t
- 0.07µs)
3.5



when sinking current using the
V
IN
V
OFF
3.9
|
I
−
OUT
OUT
V
V
PEAK
IN
TOFF
V
OUT
(V)
OUT
✕
4.3
are greater than 400ns
V
Inductor Selection
−
OUT
✕
(117kΩ /1.00µs)
TOFF
= 1.25V
V
). The following equa-
R
NMOS
+
range from 36kΩ to
= 2.5V
4.7
PMOS
V
PMOS
according to the
5.1
|
5.5



|
I
OUT
✕
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