MAX8550-MAX8551 MAXIM [Maxim Integrated Products], MAX8550-MAX8551 Datasheet - Page 9

• Manufacturer Part Number: MAX8550-MAX8551
• Description: Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards
• Manufacturer: MAXIM [Maxim Integrated Products]

*The MAX8551 has no OVP or discharge-mode feature. Only UVP is available.
PIN
10
1
2
3
4
5
6
7
8
9
Integrated DDR Power-Supply Solutions for
(MAX8550)
(MAX8551)
NAME
POK1
POK2
STBY
OVP/
VTTS
VTTR
TON
N.C.
UVP
ILIM
REF
Desktops, Notebooks, and Graphic Cards
SS
_______________________________________________________________________________________
On-Time Selection-Control Input. This four-level logic input sets the nominal DH on-time. Connect to
GND, REF, AV
TON = AV
TON = OPEN (300kHz)
TON = REF (450kHz)
TON = GND (600kHz)
Overvoltage/Undervoltage-Protection Control Input. This four-level logic input enables or disables the
overvoltage and/or undervoltage protection. The overvoltage limit is 116% of the nominal output
voltage. The undervoltage limit is 70% of the nominal output voltage. Discharge mode is enabled when
OVP is also enabled. Connect the OVP/UVP pin to the following pins for the desired function:
OVP/UVP = AV
OVP/UVP = OPEN (Enable OVP and discharge mode, disable UVP.)
OVP/UVP = REF (Disable OVP and discharge mode, enable UVP.)
OVP/UVP = GND (Disable OVP and discharge mode, disable UVP.)
Do not connect; leave open.*
+2.0V Reference Voltage Output. Bypass to GND with a 0.1µF (min) capacitor. REF can supply 50µA
for external loads. Can be used for setting voltage for ILIM. REF turns off when SHDNA, SHDNB, and
STBY are low.
Valley Current-Limit Threshold Adjustment for Buck Regulator. The current-limit threshold across PGND
and LX is 0.1 times the voltage at ILIM. Connect ILIM to a resistive divider, typically from REF to GND,
to set the current-limit threshold between 25mV and 200mV. This corresponds to a 0.25V to 2V range at
ILIM. Connect ILIM to AV
Current Limit section.
Buck Power-Good Open-Drain Output. POK1 is low when the buck output voltage is more than 10%
above or below the normal regulation point or during soft-start. POK1 is high impedance when the
output is in regulation and the soft-start circuit has terminated. POK1 is low in shutdown.
LDO Power-Good Open-Drain Output. In normal mode, POK2 is low when either VTTR or VTTS is more
than 10% above or below the normal regulation point, which is typically REFIN / 2. In standby mode,
POK2 responds only to the VTTR input. POK2 is low in shutdown, and when V
Standby. Connect to high for low-quiescent mode where the VTT output is disabled, but the VTTR
buffer is kept alive if SHDNB is high. POK2 takes input from only VTTR in this mode. PWM output can
be on or off, depending on the state of SHDNA.
Soft-Start Control for VTT and VTTR. Connect a capacitor (C9 in the Typical Applications Circuit) from
SS to ground (see the Soft-Start Capacitor Selection section). Leave SS open to disable soft-start.
SS discharges to ground when SHDNB is low. See the POR, UVLO, and Soft-Start section.
Sensing Pin for Termination Supply Output. Normally connected to VTT pin to allow accurate regulation
to half the REFIN voltage. Connected to a resistive divider from VTT to GND to regulate VTT to higher
than half the REFIN voltage.
Termination Reference Voltage. VTTR tracks V
DD
(200kHz)
DD
DD
, or leave TON unconnected to select the following nominal switching frequencies:
(Enable OVP and discharge mode, enable UVP.)
DD
to select the 50mV default current-limit threshold. See the Setting the
FUNCTION
REFIN
/ 2.
Pin Description
REFIN
is less than 0.8V.
9