1A Low-Voltage Low-Dropout Regulator
LM37101/37102
Enable Input
The LM37101 and LM37102 versions feature an active-high enable input (EN) that allows on-off control of the
regulator. Current drain reduces to “zero” when the device is shutdown, with only micro amperes of leakage
current. The EN input has TTL/CMOS compatible thresholds for simple logic interfacing. EN may be directly
tied to V
IN
and pulled up to the maximum supply voltage
Transient Response and 3.3V to 2.5V or 2.5V to 1.8V Conversion
The LM37101/2 has excellent transient response to variations in input voltage and load current. The device
has been designed to respond quickly to load current variations and input voltage variations. Large output
capacitors are not required to obtain this performance. A standard 10µF output capacitor, preferably tantalum,
is all that is required. Larger values help to improve performance even further.
By virtue of its low-dropout voltage, this device does not saturate into dropout as readily as similar NPN-
based de-signs. When converting from 3.3V to 2.5V or 2.5V to 1.8V, the NPN based regulators are already
operating in dropout, with typical dropout requirements of 1.2V or greater. To convert down to 2.5V or 1.8V
without operating in dropout, NPN-based regulators require an input voltage of 3.7V at the very least. The
LM37100 regulator will provide excellent performance with an input as low as 3.0V or 2.5V respectively. This
gives the PNP based regulators a distinct advantage over older, NPN based linear regulators.
Minimum Load Current
The LM37101/2 regulator is specified between finite loads. If the output current is too small, leakage currents
dominate and the output voltage rises. A 10mA minimum load current is necessary for proper regulation.
Adjustable Regulator Design
The LM37102 allows programming the output voltage any-where between 1.24V and the 16V maximum
operating rating of the family. Two resistors are used. Resistors can be quite large, up to 1MΩ, because of the
very high input impedance and low bias current of the sense comparator: The resistor values are calculated
by : R1=R2(Vout/1.240-1) Where Vout is the desired output voltage. Figure 1 shows component definition.
Applications with widely varying load currents may scale the resistors to draw the minimum load current
required for proper operation (see below). The current consumed by feedback resisters R1 and R2 is
calculated by: I
res
= Vout / (R1+ R2).
Figure 1. Adjustable Regulator with Resistors
Maximum Output Current Capability
The LM37101/2 can deliver a continuous current of 1A over the full operating junction temperature range.
However, the output current is limited by the restriction of power dissipation which differs from packages. A heat
sink may be required depending on the maximum power dissipation and maximum ambient temperature of
Nov. 2011 – R1.1
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HTC
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
