MIC38C42/3/4/5
Micrel, Inc.
MIC38C42/3/4/5
BiCMOS Current-Mode PWM Controllers
General Description
The MIC38C4x are fixed frequency, high performance, cur-
rent-mode PWM controllers. Micrel’s BiCMOS devices are
pin compatible with 384x bipolar devices but feature several
improvements.
Undervoltage lockout circuitry allows the ’42 and ’44 versions
to start up at 14.5V and operate down to 9V, and the ’43 and
’45 versions start at 8.4V with operation down to 7.6V. All
versions operate up to 20V.
When compared to bipolar 384x devices operating from a
15V supply, start-up current has been reduced to 50µA typical
and operating current has been reduced to 4.0 mA typical.
Decreased output rise and fall times drive larger MOSFETs,
and rail-to-rail output capability increases efficiency, espe-
cially at lower supply voltages. The MIC38C4x also features
a trimmed oscillator discharge current and bandgap refer-
ence.
The MIC38C4x denotes 8-pin plastic DIP, SOIC, and MSOP
packages. MIC384Cx-1 denotes 14-pin plastic DIP and
SOIC packages. 8-pin devices feature small size, while 14-
pin devices separate the analog and power connections for
improved perfomance and power dissipation.
For fast rise and fall times and higher output drive, refer to
the MIC38HC4x.
Features
• Fast 40ns output rise and 30ns output fall times
• –40°C to +85°C temperature range
meets UC284x specifications
• High-performance, low-power BiCMOS Process
• Ultralow start-up current (50µA typical)
• Low operating current (4mA typical)
• CMOS outputs with rail-to-rail swing
• ≥ 500kHz current-mode operation
• Trimmed 5V bandgap reference
• Pin-for-pin compatible with UC3842/3843/3844/3845(A)
• Trimmed oscillator discharge current
• UVLO with hysteresis
• Low cross-conduction currents
Applications
•
•
•
•
•
•
•
Current-mode, off-line, switched-mode power supplies
Current-mode, dc-to-dc converters.
Step-down “buck” regulators
Step-up “boost” regulators
Flyback, isolated regulators
Forward converters
Synchronous FET converters
Functional Diagram
VDD
7 (12)
*
35V
5V
Reference
Oscillator
T
Q
‡
VREF
8 (14)
UVLO
†
(VD)
(11)
RT/CT
4 (7)
OUT
6 (10)
2 (3)
FB
2.5V
2R
R
S
R
(PGND)
Q
(8)
*
COMP
1 (1)
*
†
( )
pins
GND* (AGND) ISNS
5
(9)
3 (5)
‡
are on MIC38C4x-1 (14-lead) versions only
MIC38C4x, (8-lead) versions only
MIC38C42, MIC38C43 (96% max. duty cycle) versions only
MIC38C44, MIC38C45 (50% max. duty cycle) versions only
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
September 2007
1
M9999-091107
MIC38C42/3/4/5
Micrel, Inc.
Pin Configuration
MIC38C4x-1
COMP 1
14 V R E F
NC
2
3
4
13 N C
12 VDD
11 VD
10 OUT
9
8
MIC38C4x
COMP
1
FB
FB
8
7
6
5
VREF
VDD
OUT
GND
NC
2
ISNS 5
NC
6
ISNS
3
RT/CT
4
AGND
P GND
RT/CT 7
8-Pin DIP (N)
8-Pin SOIC (M)
8-Pin MSOP (MM)
14-Pin DIP (-1BN)
14-Pin SOIC (-1BM)
Pin Description
Pin Number
N, M, MM
1
Pin Number
-1BN, -1BM
1
2
2
3
4
3
5
6
4
5
8
9
6
10
11
7
12
13
8
14
7
Pin Name
COMP
NC
FB
NC
ISNS
NC
RT/CT
GND
PGND
AGND
OUT
VD
VDD
NC
VREF
Pin Function
Compensation: Connect external compensation network to modify the error
amplifier output.
Not internally connected.
Feedback (Input): Error amplifier input. Feedback is 2.5V at desired output
voltage.
Not internally connected.
Current Sense (Input): Current sense comparator input. Connect to current
sensing resistor or current transformer.
Not internally connected.
Timing Resistor/Timing Capacitor: Connect external RC network to select
switching frequency.
Ground: Combined analog and power ground.
Power Ground: N-channel driver transistor ground.
Analog Ground: Controller circuitry ground.
Power Output: Totem-pole output.
Power Supply (Input): P-channel driver transistor supply input. Return to
power ground (PGND).
Analog Supply (Input): Controller circuitry supply input. Return to analog
ground (AGND).
Not internally connected.
5V Reference (Output): Connect external RC network.
September 2007
3
M9999-091107
MIC38C42/3/4/5
Micrel, Inc.
Absolute Maximum Ratings
Zener Current (V
DD
) ................................................... 30mA
Operation at ≥18V may require
special precautions (Note 6).
Supply Voltage (V
DD
),
Note 6
........................................ 20V
Switch Supply Voltage (V
D
) ........................................... 20V
Current Sense Voltage (V
ISNS
) .......................–0.3V to 5.5V
Feedback Voltage (V
FB
) .................................–0.3V to 5.5V
Output Current, 38C42/3/4/5 (I
OUT
) ............................. 0.5A
Storage Temperature (T
A
)......................... –65°C to +150°C
Operating Ratings
Junction Temperature (T
J
) ......................................... 150°C
Package Thermal Resistance
8-Pin Plastic DIP
(θ
JA
) .......................................125°C/W
8-Pin MSOP
(θ
JA
) ..............................................250°C/W
8-Pin SOIC
(θ
JA
) ................................................170°C/W
14-Pin Plastic DIP
(θ
JA
) ......................................90°C/W
14-Pin SOIC
(θ
JA
) ..............................................145°C/W
Electrical Characteristics
V
DD
= 15V,
Note 4;
R
T
= 11.0k; C
T
= 3.3nF; –40°C ≤ T
A
≤ 85°C; unless noted
Parameter
Reference Section
Output Voltage
Line Regulation
Load Regulation
Temp. Stability
Total Output Variation
Output Noise Voltage
Long Term Stability
Output Short Circuit
Oscillator Section
Initial Accuracy
Voltage Stability
Temp. Stability
Clock Ramp
Reset Current
Amplitude
Error Amp Section
Input Voltage
Input Bias Current
A
VOL
Unity Gain Bandwidth
PSRR
Output Sink Current
Output Source Current
V
OUT
High
V
OUT
Low
V
COMP
= 2.5V
V
FB
= 5.0V
2 ≤ V
O
≤ 4V
Note 1
12 ≤ V
DD
≤ 18V
V
FB
= 2.7V, V
COMP
= 1.1V
V
FB
= 2.3V, V
COMP
= 5V
V
FB
= 2.3V, R
L
= 15k to ground
V
FB
= 2.7V, R
L
= 15k to V
REF
65
0.7
60
2
–0.5
5
14
–1
6.8
0.1
1.1
2.42
2.50
–0.1
90
1.0
2.58
–2
V
µA
dB
MHz
dB
mA
mA
V
V
T
A
= 25°C,
Note 5
12 ≤ V
DD
≤ 18V,
Note 6
T
MIN
≤ T
A
≤ T
MAX
,
Note 1
T
A
= T
MIN
to T
MAX
T
A
= 25°C, V
RT/CT
= 2V
7.7
7.2
49
52
0.2
0.04
8.4
8.4
1.9
9.0
9.5
55
1.0
kHz
%
%/°C
mA
mA
Vp-p
T
A
= 25°C, I
O
= 1mA
12V ≤ V
DD
≤ 18V, I
O
= 5µA,
Note 6
1 ≤ I
O
≤ 20mA
Note 1
Line, Load, Temp.,
Note 1
10Hz ≤ f ≤ 10kHz, T
A
= 25°C,
Note 1
T
A
= 125°C, 1000 hrs.,
Note 1
–30
4.82
50
5
–80
25
–180
4.90
5.00
2
1
0.2
5.18
5.10
20
25
V
mV
mV
mV/°C
V
µV
mV
mA
Test Conditions
Min
Typ
Max
Units
V
RT/CT
peak to peak
M9999-091107
4
September 2007
MIC38C42/3/4/5
Parameter
Current Sense
Gain
MaximumThreshold
PSRR
Input Bias Current
Delay to Output
Output
R
DS(ON)
High
R
DS(ON)
Low
Rise Time
Fall Time
Undervoltage Lockout
Start Threshold
Minimum Operating Voltage
Pulse Width Modulator
Maximum Duty Cycle
Minimum Duty Cycle
Total Standby Current
Start-Up Current
Operating Supply Current
Zener Voltage (V
DD
)
V
DD
= 13V for MIC38C42/44
V
FB
= V
ISNS
= 0V
I
DD
= 25mA,
Note 6
30
50
4.0
37
MIC38C42/3
MIC38C44/5
94
46
96
50
MIC38C42/4
MIC38C43/5
MIC38C42/4
MIC38C43/5
13.5
7.8
8
7.0
14.5
8.4
9
7.6
I
SOURCE
= 200mA
I
SINK
= 200mA
T
A
= 25°C, C
L
= 1nF
T
A
= 25°C, C
L
= 1nF
20
11
40
30
Notes 2, 3
V
COMP
= 5V,
Note 2
12 ≤ V
DD
≤ 18V,
Note 2
2.85
0.9
3.0
1
70
–0.1
120
Test Conditions
Min
Typ
Micrel, Inc.
Max
3.15
1.1
–2
250
Units
V/V
V
dB
µA
ns
Ω
Ω
80
60
15.5
9.0
10
8.2
ns
ns
V
V
V
V
%
%
0
200
6.0
%
µA
mA
V
V
DD
= 7.5V for MIC38C43/45
Note 1:
These parameters, although guaranteed, are not 100% tested in production.
Note 2:
Parameter measured at trip point of latch with V
EA
= 0.
Note 3:
Gain defined as:
∆V
PIN1
; 0 ≤ V
TH
(I
SNS
) ≤ 0.8V
A=
V
TH
(I
SNS
)
Note 4:
Adjust V
DD
above the start threshold before setting at 15V.
Note 5:
Output frequency equals oscillator frequency for the MIC38C42 and MIC38C43. Output frequency for the MIC38C44, and
MIC38C45 equals one half the oscillator frequency.
Note 6:
On 8-pin version, 20V is maximum input on pin 7, as this is also the supply pin for the output stage. On 14-pin version, 40V is
maximum for pin 12 and 20V maximum for pin 11.
September 2007
5
M9999-091107
ADI Reference Circuit
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