UNISONIC TECHNOLOGIES CO., LTD
M7085
PFM STEP-DOWN DC-DC
CONTROLLER
DESCRIPTION
The UTC
M7085
step-down DC-DC Controller is optimized for
use with a power PMOSFET. It utilize a Pulse-Frequency
Modulation (PFM) control scheme that implies high efficiency
operation at light loads.
There are two user-selectable over-current protection methods
one provides over-current protection by taking advantage of the
R
DS(ON)
of the P- Channel. The other provides accurate over-current
protection with the use of an external sense resistor. The
cycle-by-cycle current limit threshold can be adjusted with a
external resistor.
CMOS IC
FEATURES
* High efficiency 90% and up is possible
* Low dropout operation：100% duty cycle
* Maximum operating frequency > 1MHz
* Two methods of over-current protection
* 4.5V ~ 35V wide input range
* 1.24V ~ V
IN
adjustable output range
ORDERING INFORMATION
Ordering Number
Lead Free
Halogen Free
M7085L-SM1-R
M7085G-SM1-R
M7085L-SM1-T
M7085G-SM1-T
Package
MSOP-8
MSOP-8
Packing
Tape Reel
Tube
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M7085
PIN CONFIGURATION
I
SENSE
SGND
NC
FB
CMOS IC
1
2
3
4
8
7
6
5
V
IN
PGATE
PGND
ADJ
PIN DESCRIPTION
PIN NO
1
2
3
4
5
6
7
8
PIN NAME
I
SENSE
S
GND
NC
FB
ADJ
P
GND
GATE
V
IN
DESCRIPTION
The over-current protection input pin that be connected to Drain node of the external
P-Channel.
Signal Ground.
No Connection.
The feedback voltage input.
The over-current protection input pin that adjust current limit threshold.
Power Ground.
Driver pin to Gate of the external P-Channel. PGATE swings between V
IN
and V
IN
-5V.
Power Supply
BLOCK DIAGRAM
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M7085
ABSOLUTE MAXIMUM RATING
PARAMETER
CMOS IC
SYMBOL
RATINGS
UNIT
Input Voltage
V
IN
-0.3 ~ 36
V
P
GATE
Voltage
V
PGATE
-0.3 ~ 36
V
FB Voltage
V
FB
-0.3 ~ 5
V
I
SENSE
Voltage
V
ISNS
-1.0 ~ 36
V
ADJ Voltage
V
ADJ
-0.3 ~ 36
V
Power Dissipation (T
A
=25℃)
P
D
400
mW
Junction Temperature
T
J
150
℃
Storage Temperature
T
STG
-65 ~ +150
℃
Note: Absolute maximum ratings are those values beyond which the device could be permanently damaged.
Absolute maximum ratings are stress ratings only and functional device operation is not implied.
OPERATING RATINGS
PARAMETER
Supply Voltage
Operating Junction Temperature
SYMBOL
T
OPR
RATINGS
4.5 ~ 35
-40 ~ +125
UNIT
V
℃
ELECTRICAL CHARACTERISTICS
V
IN
= 12V, V
ISNS
= V
IN
−
1V, and V
ADJ
= V
IN
−
1.1V, Ta=25℃
PARAMETER
SYMBOL
TEST CONDITIONS
Feedback Voltage (Note 1)
Minimum Driver Voltage
Comparator Hysteresis
V
FB
V
PGATE(MIN)
V
HYS
V
IN
= 4.5V V
FB
= 1.0V
I
GATE
= 100μA sink
MIN
1.224
1.215
TYP MAX
1.240 1.256
1.265
1.15
10
15
110
880
0
5
320
0.4
0.3
5
8
8
110
185
0.010
300
500
16
21
UNIT
V
V
mV
mV
+20
7.0
756
mV
µA
nA
A
Ω
13
µS
ns
ns
%/V
µA
R
ADJ
= 20Ω
R
ADJ
= 160Ω
Current Limit Comparator Offset
V
CL(OFF)
V
FB
= 1.5V
-20
Current Limit ADJ Current Source
I
CL(ADJ)
V
FB
= 1.5V
3.0
FB pin Bias Current (Note 3)
I
FB
V
FB
= 1.0V
Source
V
IN
= 7V, P
GATE
= 3.5V
Driver Output Current
I
PGATE
Sink
V
IN
= 7V, P
GATE
= 3.5V
Source
I
SOURCE
= 100mA
Driver Resistance
R
PGATE
Sink
I
SINK
= 100mA
V
ADJ
= 11.5V, V
ISNS
= 11.0V,
Current Limit One Shot off Time
T
CL
5
V
FB
= 1.0V
V
ISNS
= V
ADJ
+0.1V, C
LOAD
on
Minimum on Time in Normal Operation T
OPR(MIN)
OUT = 1000pF, (Note 4)
V
ISNS
= V
ADJ
+0.1V, V
FB
= 1.0V
Minimum on Time in Current Limit
T
CL(MIN)
C
LOAD
on OUT=1000pF (Note 4)
Feedback Voltage Line Regulation
%V
FB
/
△
V
IN
4.5
≤
V
IN
≤
35V
Quiescent Current at Ground Pin
I
Q
FB = 1.5V (Not Switching)
Note: 1. The V
FB
is the trip voltage at the FB pin when PGATE switches from high to low.
2. V
CL
= I
CL_ADJ
* R
ADJ
3. Bias current flows out from the FB pin.
4. A 1000pF capacitor is connected between V
IN
and P
GATE
.
Current Limit Comparator Trip Voltage V
CL
(Note2)
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M7085
TYPICAL APPLICATION CIRCUIT
V
IN
4.5V ~ 35V
C
IN
22µF
R
ADJ
C
ADJ
5
ADJ
6
V
IN
2.6
UTC M7085
P
GATE
I
SENSE
FB
7
1
4
CMOS IC
Q1
L1
22µH
D1
V
OUT
3.3V
R1
33KΩ
C
OUT
100uF
R2
20KΩ
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M7085
APPLICATION INFORMATION
CMOS IC
Setting the output voltage
Select an output voltage between 1.24V and V
IN
by connecting FB to a resistive voltage-divider between V
OUT
and GND (see the Typical Operating Circuit). Choose R2 for a reasonable bias current in the resistive divider. A wide
range of resistor values is acceptable.
R1, R2 is given by:
V
OUT
= 1.240* (R1 + R2) / R2
Setting over current protection threshold by the R
DS(ON)
of the P-Channel
The UTC
M7085
has a cycle-by-cycle current limit. Current limit is sensed across the V
DS
of the P-Channel or
across an additional sense resistor. When current limit is activated, the UTC
M7085
turns off the external P-Channel
for a period of 9μs(typical). The current limit is adjusted by an external resistor, R
ADJ
.
The current limit circuit is composed of the I
SENSE
comparator and the one-shot pulse generator. The positive input
of the I
SENSE
comparator is the ADJ pin. An internal 5.5µA current sink creates a voltage across the external R
ADJ
resistor. This voltage is compared to the voltage across the P-Channel or sense resistor. The ADJ voltage can be
calculated as follows:
V
ADJ
= V
IN
- (R
ADJ
* 3.0μA)
Where 3.0μA is the minimum I
CL(ADJ)
value.
The negative input of the I
SENSE
comparator is the I
SENSE
pin that should be connected to the drain of the external
P-Channel. The inductor current is determined by sensing the V
DS
. It can be calculated as follows.
V
ISENSE
= V
IN
- (R
DS(ON)
* I
IND_PEAK
) = V
IN
- V
DS
C
ADJ
5.5µA
ADJ
5
1
I
SENSE
R
ADJ
V
DS
V
IN
I
SENSE
COMP
Fig. 1 Current Sensing by V
DS
The current limit is activated when the voltage at the ADJ pin exceeds the voltage at the I
SENSE
pin. The I
SENSE
comparator triggers the 9μs one shot pulse generator forcing the driver to turn the P-Channel off. The driver turns
the P-Channel back on after 9μs. If the current has not reduced below the set threshold, the cycle will repeat
continuously.
A filter capacitor, C
ADJ
, should be placed as shown in Fig. 1 C
ADJ
filters unwanted noise so that the I
SENSE
comparator will not be accidentally triggered. A value of 100pF to 1nF is recommended in most applications. Higher
values can be used to create a soft-start function. The current limit comparator has approximately 100ns of blanking
time. This ensures that the P-Channel is fully on when the current is sensed. However, under extreme conditions
such as cold temperature, some P-Channels may not fully turn on within the blanking time. In this case, the current
limit threshold must be increased. If the current limit function is used, the on time must be greater than 100ns. Under
low duty cycle operation, the maximum operating frequency will be limited by this minimum on time.
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