MIC2937A/29371/29372 Micrel, Inc.
May 2006 5 MIC2937A/29371/29372
Note 1: Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not
apply when operating the device outside of its rated operating conditions. The maximum allowable power dissipation is a function of the
maximum junction temperature, T
J (MAX)
, the junction-to-ambient thermal resistance, θ
JA
, and the ambient temperature, T
A
. The maximum
allowable power dissipation at any ambient temperature is calculated using: P
(MAX)
= (T
J(MAX)
– T
A
)
/ θ
JA.
Exceeding the maximum allowable
power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown.
Note 2: Output voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.
Note 3: Regulation is measured at constant junction temperature using low duty cycle pulse testing. Changes in output voltage due to
heating effects are covered by the thermal regulation specification.
Note 4: Dropout Voltage is defined as the input to output differential at which the output voltage drops 100 mV below its nominal value
measured at 1V differential. At low values of programmed output voltage, the minimum input supply voltage of 4.3V over temperature must
be taken into account. The MIC2937A operates down to 2V of input at reduced output current at 25°C.
Note 5: Ground pin current is the regulator quiescent current. The total current drawn from the source is the sum of the load current
plus the ground pin current.
Note 6: The MIC2937A family features fold-back current limiting. The short circuit (V
OUT
= 0V) current limit is less than the maximum
current with normal output voltage.
Note 7: Thermal regulation is defined as the change in output voltage at a time T after a change in power dissipation is applied, exclud-
ing load or line regulation effects. Specifications are for a 200mA load pulse at V
IN
= 20V (a 4W pulse) for T = 10ms.
Note 8: V
REF
≤ V
OUT
≤ (V
IN
– 1 V), 4.3V ≤ V
IN
≤ 26V, 5mA < I
L
≤ 750 mA, T
J
≤ T
J MAX.
Note 9: Comparator thresholds are expressed in terms of a voltage differential at the Adjust terminal below the nominal reference voltage
measured at 6V input (for a 5V regulator). To express these thresholds in terms of output voltage change, multiply by the error amplifier
gain = V
OUT
/V
REF
= (R1 + R2)/R2. For example, at a programmed output voltage of 5V, the Error output is guaranteed to go low when
the output drops by 95 mV x 5V/1.235 V = 384 mV. Thresholds remain constant as a percent of VOUT as VOUT is varied, with the dropout
warning occurring at typically 5% below nominal, 7.7% guaranteed.
Note 10: Circuit of Figure 3 with R1 ≥ 150kΩ. V
SHUTDOWN
≥ 2V and V
IN
≤ 26V,V
OUT
= 0.
Note 11: When used in dual supply systems where the regulator load is returned to a negative supply, the output voltage must be diode
clamped to ground.
Note 12: Maximum positive supply voltage of 60V must be of limited duration (< 100ms) and duty cycle ( ≤ 1%). The maximum continu-
ous supply voltage is 26V.
FEEDBACK
SENSE
Q15A
OUT
Q24
Q26
R27
V TAP
R28
R18
20 k
Ω
Q25
Q23
Q22
R15
100 k
Ω
R16
30 k
Ω
Q29
Q28
R17
10
Ω
R21 8 Ω
R17
12 k
Ω
Q31
Q30
R23 60 k Ω
SHDN
R24
50 k
Ω
R22
150 k
Ω
Q21
Q19
C2
40 pF
R14
350
k Ω
Q14
R13
100
k Ω
Q18
R12
110
k Ω
Q20
Q9
Q15B
Q8
Q7
R11
20.6
k Ω
Q5
R8
31.4 k
Ω
R10
150
k Ω
R9
27.8 k
Ω
Q11
Q12
Q13
R6
140
k Ω
R5
180
k Ω
R4
13 k
Ω
R3
50 k
Ω
Q2
C1
20
pF
Q4
Q3
R11
18
k Ω
Q6
Q1
10
R1
20 k
Ω
R2
50 k
Ω
Q41
R30
30
k Ω
Q40
Q34
GND
Q36
Q37
R25
2.8 k
Ω
Q38
ERROR
R26
60 k
Ω
Q39
Q42
Q16
Q17
50 kΩ
10 k
Ω
IN
DENOTES CONNECTION ON
MIC2937A-xx AND MIC29371-xx
VERSIONS ONLY
Schematic Diagram
