April 2005 3 M9999-042205
MIC2184 Micrel, Inc.
Pin Description
Pin Number Pin Name Pin Function
1 VINA Analog voltage input voltage to the circuit. This powers up the analog
sections of the die and does not need to be the same voltage as Pin 16
(V
IN
P).
2 FreqOut This provides a digital signal output signal at half the switching frequency.
This signal swings from 0 to 3V, and can be used to drive an external
capacitive doubler to provide a higher voltage to the V
IN
P input.
3SSSoft start reduces the inrush current and delays and slows the output voltage
rise time. A 5µA current source will charge the capacitor up to V
DD
. A 1µF
capacitor will soft start the switching regulator in 1.5ms.
4 COMP Compensation (Output): Internal error amplifier output. Connect to a
capacitor or series RC network to compensate the regulator’s control loop.
5 SGND Small signal ground: must be routed separately from other grounds to the (-)
terminal of C
OUT
.
6FBFeedback Input - the circuit regulates this pin to 1.245V.
7 EN/UVLO Enable/UnderVoltage Lockout (input): A low level on this pin will power down
the device, reducing the quiescent current to under 5uA. This pin has two
separate thresholds, below 1.5V the output switching is disabled, and below
0.9V the part is forced into a complete micropower shutdown. The 1.5V
threshold functions as an accurate undervoltage lockout (UVLO) with 140mV
hysteresis.
8 CSL The (-) input to the current limit comparator. A built in offset of 100mV
between CSH and CSL in conjunction with the current sense resistor sets
the current limit threshold level. This is also the (-) input to the current
amplifier.
9 CSH The (+) input to the current limit comparator. A built in offset of 100mV
between CSH and CSL in conjunction with the current sense resistor sets
the current limit threshold level. This is also the (+) input to the current
amplifier.
10 VDD 3V internal linear-regulator output. V
DD
is also the supply voltage bus for the
chip. Bypass to SGND with 1µF.
11 SYNC Frequency Synchronization (Input): Connect an external clock signal to
synchronize the oscillator. Leading edge of signal above 1.5V starts the
switching cycle. Connect to SGND if not used.
12 PGND MOSFET driver power ground, connects to source of synchronous MOSFET
and the (-) terminal of CIN.
13 VREF The 1.245V voltage reference is available on this pin. A 0.1µF capacitor
should be connected from this pin to ground.
14 OUTP High current drive for high side P channel MOSFET. Voltage swing is from
ground to V
IN
P. On-resistance is typically 2.5Ω.
15 FREQ/2 When this is low, the oscillator frequency is 400KHz. When this pin is raised
to V
DD
, the oscillator frequency is 200KHz.
16 VINP Power Input voltage to the circuit. The output gate drivers are powered from
this supply. The current sense resistor R
CS
should be connected as close as
possible to this pin.
