Tracking, Sinking and Sourcing, Synchronous Buck
Controller for DDR Memory and Termination Supplies
MAX1917
Typical Operating Characteristics (continued)
(V+ = 12V, V
OUT
= 1.25V, T
A
= +25°C, unless otherwise noted.)
CURRENT LIMIT vs. TEMPERATURE
MAX1917 toc16
INDUCTOR PEAK AND VALLEY CURRENT
vs. INPUT VOLTAGE AT CURRENT LIMIT
R
ILIM
= 400kΩ
16
INDUCTOR CURRENT (A)
MAX1917 toc17
18
16
14
CURRENT LIMIT (A)
12
10
8
6
4
2
0
-40
-20
0
20
40
60
80
R
ILIM
= 200kΩ
R
ILIM
= 402kΩ
18
14
I
PEAK
12
I
VALLEY
10
CIRCUIT OF FIGURE 3
8
100
1
3
5
7
9
11
13
15
TEMPERATURE (°C)
V
IN
(V)
Pin Description
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
NAME
EN/HSD
DDR
POK
VTT
ILIM
FSEL
REF
GND
VTTR
V+
VL
DL
PGND
BST
DH
LX
FUNCTION
Enable/High-Side Drain. Connect to the high-side N-FET drain for normal operation. Leave unconnected or
connect to GND for low-power shutdown.
DDR Reference Input. An applied voltage at DDR sets V
VTT
and V
VTTR
to 1/2V
DDR
. DDR voltage range is
from 0 to 3.6V.
Power-OK Output. POK is an open-drain output and is logic high when both VTT and VTTR are within 12%
of regulation. POK is pulled low in shutdown.
VTT Feedback Input. Connect to VTT output.
Current-Limit Threshold Adjustment. Connect a resistor from ILIM to GND to set the current-limit threshold,
or connect ILIM to VL for default setting. See the
Setting the Current Limit
section.
Frequency Select. Selects the switching frequency of the MAX1917. See Table 1 for configuration of FSEL.
Reference Bypass. Connect a 0.22µF or larger capacitor from REF to GND.
Ground
VTTR Reference Output. Connect a 1µF or larger capacitor from VTTR to GND. VTTR is capable of
sourcing and sinking up to 25mA.
Input Supply Voltage. Supply input for the VL regulator and the VTTR regulator. Bypass with a 0.22µF or
larger capacitor.
Internal Regulator Output. Connect a 2.2µF or larger capacitor from VL to GND. VL can be connected to
V+ if the operating range is 4.5V to 5.5V.
Low-Side MOSFET Gate Drive. Connect to the gate of the low-side N-channel MOSFET.
Power Ground
Bootstrapped Supply to Drive High-Side N-Channel MOSFET. Connect a 0.47µF or larger capacitor from
BST to LX.
High-Side MOSFET Gate Drive. Connect to the high-side N-channel MOSFET gate.
Inductor Switching Node
8
_______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
