MAX8550AETI+ Maxim Integrated Products, MAX8550AETI+ Datasheet - Page 17

• Manufacturer Part Number: MAX8550AETI+
• Description: IC PWR SUP DDR INTEG 28TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8550AETI+

• Applications: Controller, DDR
• Voltage - Input: 2 ~ 28 V
• Number Of Outputs: 2
• Voltage - Output: 1.8V, 2.5V, 0.7 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-TQFN Exposed Pad
• Output Voltage: 0.7 V to 5.5 V, 1.8 V, 2.5 V
• Output Current: 1.5 A
• Input Voltage: 2 V to 28 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

When the output voltage rises above 116% of the nomi-
nal regulation voltage and OVP is enabled (OVP/UVP =
AV
shuts down the PWM controller, and immediately pulls
DH low and forces DL high. This turns on the synchro-
nous-rectifier MOSFET (Q2 in the Typical Applications
Circuit of Figure 8) with a 100% duty cycle, rapidly dis-
charging the output capacitor and clamping the output
to ground. Note that immediately latching DL high can
cause the output voltage to go slightly negative due to
energy stored in the output LC circuit at the instant the
OVP occurs. If the load cannot tolerate a negative volt-
age, place a power Schottky diode across the output to
act as a reverse-polarity clamp. Toggle SHDN or cycle
AV
controller. OVP is disabled when OVP/UVP is connect-
ed to REF or GND (see Table 3). OVP only applies to
the buck output. The VTT and VTTR outputs do not
have overvoltage protection.
When the output voltage drops below 70% of its regula-
tion voltage while UVP is enabled, the controller sets
the fault latch and begins the discharge mode (see the
Shutdown and Output Discharge section). When the
output voltage drops to 0.1V, the synchronous rectifier
(Q2 in the Typical Applications Circuit) turns on and
clamps the buck output to GND. UVP is ignored for at
least 10ms (min) after startup or after a rising edge on
SHDN. Toggle SHDN or cycle AV
clear the fault latch and restart the controller. UVP is
disabled when OVP/UVP is left open or connected to
GND (see Table 3). UVP only applies to the buck out-
put. The VTT and VTTR outputs do not have undervolt-
age protection.
Table 3. OVP/UVP Fault Protection
DD
DD
OVP/UVP
OPEN
AV
GND
REF
below 1V to clear the fault latch and restart the
or open), the OVP circuit sets the fault latch,
DD
Integrated DDR Power-Supply Solution for
Desktops, Notebooks, and Graphic Cards
DL forced high when SHDN is low
DL forced high when SHDN is low
DL forced low when SHDN is low.
DL forced low when SHDN is low.
______________________________________________________________________________________
Undervoltage Protection (UVP)
Overvoltage Protection (OVP)
and OUT < 0.1V.
and OUT < 0.1V.
DISCHARGE
Yes.
Yes.
No.
No.
DD
power below 1V to
UVP PROTECTION
The MAX8550A features two thermal-fault-protection
circuits. One monitors the buck-regulator portion of the
IC and the other monitors the linear regulator (VTT) and
the reference buffer output (VTTR). When the junction
temperature of the buck-regulator portion of the
MAX8550A rises above +160°C, a thermal sensor acti-
vates the fault latch, pulls POK1 low, and shuts down
the buck-controller output using discharge mode
regardless of the OVP/UVP setting. Toggle SHDN or
cycle AV
the junction temperature cools by 15°C. If the VTT and
VTTR regulator portion of the IC has its die temperature
rise above +160°C, then VTT and VTTR shut off, go
high impedance, and restart after the die portion of the
IC cools by 15°C. Both thermal faults are independent.
For example, if the VTT output is overloaded to the
point that it triggers its thermal fault, the buck regulator
continues to function.
Firmly establish the input voltage range (V
mum load current (I
choosing a switching frequency and inductor operating
point (ripple current ratio or LIR). The primary design
trade-off lies in choosing a good switching frequency
and inductor operating point, and the following four fac-
tors dictate the rest of the design:
• Input Voltage Range. The maximum value (V
Disabled
Disabled
Enabled
Enabled
must accommodate the worst-case voltage. The mini-
mum value (V
voltage after drops due to connectors and fuses. If
there is a choice, lower input voltages result in better
efficiency.
DD
below 1V to reactivate the controller after
IN(MIN)
LOAD
Thermal Fault Protection
) must account for the lowest
) in the buck regulator before
Design Procedure
OVP PROTECTION
Disabled
Disabled
Enabled
Enabled
IN
) and maxi-
IN(MAX)
17
)