MIC5157YM Datasheet, PDF (7/13 Pages) Micrel Semiconductor – Super LDO™ Regulator Controller

MIC5156/5157/5158
Block Diagram MIC5158
0.1µF C1 0.1µF C2
C1+ C1– C2+ C2– V_{C P}
C3
1µF
+5V Input
V_DD
Micrel, Inc.
Oscillator
Charge Pump
Tripler
FLAG
1.235V
Bandgap
Reference
V_{O U T}
Comparator
Error
Amp
75mV
V_{C P}
Clamp
Internal
Bias
EN
Enable
Shutdown
R_S
3mΩ
to all
internal blocks
I_LIMIT
Comparator
D (Drain)
35mV
[ I_LIMIT ]
G (Gate)
16.6V _{S (Source)}
32k
5V
FB
10k
GND
Q1
IRFZ44
Regulated
+3.6V Output
C_L
EA 19.1k
10.0k
Block Diagram with External Components
Adjustable Power Supply, 3.6V Configuration
Functional Description
A Super LDO Regulator is a complete regulator built around
Micrel’s Super LDO Regulator Controller.
Refer to Block Diagrams MIC5156, MIC5157, and
MIC5158.
Version Differences
The MIC5156 requires an external voltage for MOSFET gate
drive and is available in 3.3V fixed output, 5V fixed output, or
adjustable output versions. With 8-pins, the MIC5156 is the
smallest of the Super LDO Regulator Controllers.
The MIC5157 and MIC5158 each have an internal charge
pump which provides MOSFET gate drive voltage. The
MIC5157 has a selectable fixed output of 3.3V, 5V, or 12V.
The MIC5158 may be configured for a fixed 5V or adjustable
output.
Enable (EN)
With at least 3.0V on V_DD, applying a TTL low to EN places
the controller in shutdown mode. A TTL high on EN enables
the internal bias circuit which powers all internal circuitry. EN
must be pulled high if unused. The voltage applied to EN may
be as high as 36V.
The controller draws less than 1µA in shutdown mode.
Gate Enhancement
The Super LDO Regulator Controller manages the gate-
to-source enhancement voltage for an external N-channel
MOSFET (regulator pass element) placed between the supply
and the load. The gate-to-source voltage may vary from 1V
to 16V depending upon the supply and load conditions.
Because the source voltage (output) approaches the drain
voltage (input) when the regulator is in dropout and the
MOSFET is fully enhanced, an additional higher supply
voltage is required to produce the necessary gate-to-source
enhancement. This higher gate drive voltage is provided by
an external gate drive supply (MIC5156) or by an internal
charge pump (MIC5157 and MIC5158).
Gate Drive Supply Voltage (MIC5156 only)
The gate drive supply voltage must not be more than 14V
above the supply voltage (V_P – V_DD < 14V). The minimum
necessary gate drive supply voltage is:
V_P = V_OUT + V_GS + 1
where:
V_P = gate drive supply voltage
V_OUT = regulator output voltage
V_GS = gate-to-source voltage for full
MOSFET gate enhancement
The error amplifier uses the gate drive supply voltage to drive
the gate of the external MOSFET. The error amplifier output
can swing to within 1V of V_P.
August 2005
7
MIC5156/5157/5158