MAX1809EEE+T Maxim Integrated Products, MAX1809EEE+T Datasheet - Page 8

• Manufacturer Part Number: MAX1809EEE+T
• Description: IC DDR TERMINATION 16-QSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX1809EEE+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

3A, 1MHz, DDR Memory Termination Supply
where C = 2.5nF and f
Resistive losses in the two power switches are approxi-
mated by:
where R
The junction-to-ambient thermal resistance required to
dissipate this amount of power is calculated by:
where:
For typical applications, use the recommended compo-
nent values in Figure 1. For other applications, take the
following steps:
1) Select the desired PWM-mode switching frequency.
2) Select the constant off-time as a function of input
3) Select R
4) Select the inductor as a function of output voltage,
Figure 2. Functional Diagram
8
See Figure 4 for maximum operating frequency.
voltage, output voltage, and switching frequency.
off-time, and peak-to-peak inductor current.
_______________________________________________________________________________________
θ
θ
T
T
JA
JA
J,MAX
A,MAX
PMOS
= (T
= junction-to-ambient thermal resistance
TOFF
= maximum junction temperature
= maximum ambient temperature
J,MAX
is the on-resistance of the PMOS switch.
P
V
D(RES)
IN
as a function of off-time.
- T
2.2µF
A,MAX
1µF
= I
SW
EXTREF
SHDN
OUT
V
Design Procedure
REF
CC
is the switching frequency.
) / (P
2 ✕
D(CAP)
R
PMOS
REF
GND
+ P
MAX1809
D(RES)
TIMER
)
R
TOFF
PWM LOGIC
CURRENT
DRIVERS
SS
SENSE
AND
The output voltage of the MAX1809 is set by an external
voltage applied to the EXTREF pin. This can come directly
from another voltage source or external reference.
As an active termination supply in DDR applications
(see Active Bus Termination in the Applications
Information section), the output of the MAX1809 is reg-
ulated at half the DDR supply voltage. In mobile sys-
tems, the DDR supply voltage is 2.5V, and the
termination voltage is 1.25V ±40mV. To regulate to
1.25V, an external divide-by-2 resistor network is
placed across the DDR supply voltage to generate
1.25V. This 1.25V is connected to EXTREF, which sets
the output voltage of the MAX1809. When FB is directly
tied to the output (Figure 5), the output voltage range is
limited by the external reference’s input voltage limits
(see EC table). External reference may not be set within
1.7V of the minimum supply voltage. V
be limited to less than 1.4V for 3.3V input voltage.
Failure to comply can cause the part to operate abnor-
mally and may cause part damage.
Alternatively, the output can be adjusted up to V
connecting FB to a resistor-divider between the output
voltage and ground (Figure 6). Use 50kΩ for R1. R2 is
given by:
0.01µF
PGND
IN
LX
FB
R
2
=
C
CERAMIC
L
R
IN
Setting the Output Voltage
1
C
OUT



V
EXTREF
V
OUT
V
(3.0V TO 5.5V)
IN
−
1



EXTREF
should
IN
by