MAX8794 Maxim Integrated Products, MAX8794 Datasheet - Page 10

• Manufacturer Part Number: MAX8794
• Description: Low-Voltage DDR Linear Regulator
• Manufacturer: Maxim Integrated Products

Low-Voltage DDR Linear Regulator
The MAX8794 provides an open-drain PGOOD output
that goes high 2ms (typ) after the output initially reach-
es regulation during startup. PGOOD transitions low
10µs after the output goes out of regulation by ±150mV,
or when the device enters shutdown. Connect a pullup
resistor from PGOOD to V
Use a 100kΩ resistor to minimize current consumption.
By changing the voltage at REFIN, the MAX8794 can
be used in applications that require dynamic output-
voltage changes between two set points (graphics
processors). Figure 4 shows a dynamically adjustable
resistive voltage-divider network at REFIN. Using an
external signal MOSFET, a resistor can be switched in
and out of the REFIN resistor-divider, changing the volt-
age at REFIN. The two output voltages are determined
by the following equations:
Figure 3. MAX8794 PGOOD and Soft-Start Waveforms
10
______________________________________________________________________________________
V
Dynamic Output-Voltage Transitions
CURRENT LIMIT
OUT HIGH
POWER-GOOD
V
WINDOW
OUT LOW
(
PGOOD
SHDN
Applications Information
OUT
(
)
=
)
V
=
REF
V
CC
200µs
Power-Good (PGOOD)
REF
⎡
⎢
⎢
⎣
R
for a logic-level output.
2ms STARTUP
1
⎛
⎜
⎝
DELAY
(
R
+
R
1
2
(
R
+
R
+
2
2
R
R
3
+
2
)
R
⎞
⎟
⎠
3
)
⎤
⎥
⎥
⎦
PROPAGATION
DELAY
10µs
Figure 4. Dynamic Output-Voltage Change
V
V
OUTPUT OVERLOAD
CONDITION
OUT(LOW)
OUT(HIGH)
V
OUT(HIGH)
= V
=
V
REF
REF
10µs
PROPAGATION
DELAY
( )
V
R1 + (R2 + R3)
R1 + R2
OUT(LOW)
(R2 + R3)
R2
C
REFIN
REFERENCE
R1
R2
R3
VOLTAGE
(V
REF
)
REFIN
MAX8794