Detailed Description
The MAX1982/MAX1983 are low-voltage, low-dropout
linear regulators with an external bias supply input (see
Figures 1 and 2). BIAS is powered by a 4.5V to 5.5V
supply that is commonly available in laptop and desk-
top computers. The 5V bias supply drives the gate of
the internal pass transistor, while a lower voltage input
at the drain of the transistor (IN) is regulated to provide
V
OUT
. Separating the bias input voltages yields higher
efficiency. These devices are ideal for applications that
require low-voltage outputs from low-voltage inputs.
The MAX1982 delivers 1.2V (±3%) at 300mA from an
input voltage of 1.25V to 5.5V. The MAX1983 delivers
an adjustable output voltage from 0.8V to 2V.
The MAX1982 features an open-drain PGOOD output
that transitions high 1ms after the output reaches regu-
lation. PGOOD goes low within 10µs of the output
falling out of regulation by 120mV.
Both devices feature current- and thermal-limiting cir-
cuitry that protect the MAX1982/MAX1983 from dam-
age during fault conditions.
Bias Supply Input
The BIAS input powers the control circuitry and pro-
vides the pass transistor gate drive. Power BIAS from a
well-regulated 5V (±10%) supply. Current drawn from
the BIAS supply remains relatively constant with varia-
tions in V
IN
and load current (see the
Typical Operating
Characteristics
). Bypass BIAS with a 0.1µF or greater
capacitor as close to the device as possible. The bias
supply current remains low (250µA) when the
MAX1982/MAX1983 are in dropout.
Power-Supply Input
IN connects to the drain of the internal N-channel
power transistor. IN may be as low as 1.25V, minimizing
power dissipation. Bypass IN with a 10µF or greater
capacitor as close to the device as possible.
Shutdown
The MAX1982/MAX1983 feature a low-power shutdown
mode that reduces quiescent current drawn to 1µA
(typ), and BIAS current consumption to less than 1µA
(typ). Driving SHDN low disables the voltage reference,
error amplifier, gate-drive circuitry, and pass transistor
(see Figure 2), and the device output enters a high-
impedance state. Connect SHDN to BIAS for normal
operation.
PGOOD Output
The MAX1982 provides an open-drain PGOOD output
that goes high 1ms (min) after the output attains regula-
tion (within 10% of the nominal output voltage). PGOOD
transitions low 10µs after the output falls out of regula-
tion by 120mV, or when the device enters shutdown.
Connect a pullup resistor from PGOOD to BIAS for a
logic-level output. Use a 100kΩ resistor to minimize
current consumption.
