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RT7235/36/39/40
5A, 18V, 650kHz, ACOTTM Synchronous Step-Down Converter
General Description
Features
The RT7235/36/39/40 is a synchronous step-down DC/
DC converter with Advanced Constant On-Time (ACOTTM)
mode control. It achieves high power density to deliver up
to 5A output current from a 4.5V to 18V input supply. The
proprietary ACOTTM mode offers an optimal transient
response over a wide range of loads and all kinds of ceramic
capacitors, which allows the device to adopt very low ESR
output capacitor for ensuring performance stabilization. In
addition, RT7235/36/39/40 keeps an excellent constant
switching frequency under line and load variation and the
integrated synchronous power switches with the ACOTTM
mode operation provides high efficiency in whole output
current load range. Cycle-by-cycle current limit provides
an accurate protection by a valley detection of low side
MOSFET and external soft-start setting eliminates input
current surge during startup. Protection functions include
thermal shutdown for RT7235/36/39/40, output Under
Voltage Protection (UVP) / Over Voltage Protection (OVP)
for RT7235/36. When the UVP/OVP is triggered, the device
will enter latch mode for TSSOP-14 (Exposed Pad), and
hiccup mode for WDFN-10L 3x3.
The RT7235/36 are available in TSSOP-14 (Exposed Pad)
and WDFN-10L 3x3 packages, and the RT7235 is operated
in forced continuous conduction mode.
ACOTTM Mode Enables Fast Transient Response
4.5V to 18V Input Voltage Range
5A Output Current
35mΩ
Ω Internal Low Site N-MOSFET
Advanced Constant On-Time Control
Support All Ceramic Capacitors
Up to 95% Efficiency
650kHz Switching Frequency at all Load Current
(RT7235, RT7239)
Discontinuous Operating Mode at Light Load
(RT7236, RT7240)
Adjustable Output Voltage from 0.765V to 8V
Adjustable Soft-Start
Cycle-by-Cycle Current Limit
Input Under Voltage Lockout
Thermal Shutdown
RoHS Compliant and Halogen Free
Applications
Industrial and Commercial Low Power Systems
Computer Peripherals
LCD Monitors and TVs
Green Electronics/Appliances
Point of Load Regulation for High-Performance DSPs,
FPGAs, and ASICs
The RT7239/40 are available in the SOP-8 (Exposed Pad)
package, and the RT7239 is operated in forced continuous
conduction mode.
Simplified Application Circuit
RT7235/36/39/40
VIN
Enable
Power GOOD
* : VCC pin for TSSOP-14 (Exposed Pad) only.
VIN
SW
VCC*
BOOT
EN
PGOOD*
PGND
VREG5
SS
GND*
VOUT
FB
VS*
VS pin for TSSOP-14 (Exposed Pad) only.
GND pin for TSSOP-14 (Exposed Pad) only.
PGOOD pin for TSSOP-14 (Exposed Pad) and WDFN-10L 3x3 only.
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
DS7235/36/39/40-08
January 2017
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
RT7235/36/39/40
Ordering Information
Marking Information
Continuous Switching Mode
RT7235GCP
RT7235GCP : Product Number
RT7235
RT7235GCP
YMDNN
Package Type
CP : TSSOP-14 (Exposed Pad)
QW : WDFN-10L 3x3 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
YMDNN : Date Code
RT7235GQW
1N= : Product Code
1N=YM
DNN
RT7239
YMDNN : Date Code
Package Type
SP : SOP-8 (Exposed Pad-Option 2)
Lead Plating System
G : Green (Halogen Free and Pb Free)
RT7239GSP
RT7239GSP : Product Number
RT7239
GSPYMDNN
YMDNN : Date Code
Discontinuous Operating Mode
RT7236GCP
RT7236
RT7236GCP : Product Number
Package Type
CP : TSSOP-14 (Exposed Pad)
QW : WDFN-10L 3x3 (W-Type)
RT7236GCP
YMDNN
Lead Plating System
G : Green (Halogen Free and Pb Free)
RT7236GQW
1M= : Product Code
RT7240
1M=YM
DNN
Package Type
SP : SOP-8 (Exposed Pad-Option 2)
Lead Plating System
G : Green (Halogen Free and Pb Free)
YMDNN : Date Code
RT7240GSP
Note :
RT7240GSP : Product Number
RT7240
GSPYMDNN
Richtek products are :
YMDNN : Date Code
RoHS compliant and compatible with the current require-
YMDNN : Date Code
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
Pin Configurations
14
2
13
12
3
4
PGND
11
5
10
6
9
7
15
8
VCC
VIN
BOOT
SW
SW
PGND
PGND
EN
FB
VREG5
SS
PGOOD
TSSOP-14 (Exposed Pad)
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2
1
2
3
4
5
11
10
9
8
7
9
VS
FB
VREG5
SS
GND
PGOOD
EN
PGND
(TOP VIEW)
VIN
VIN
BOOT
SW
SW
WDFN-10L 3x3
8
EN
FB
2
VREG5
3
SS
4
PGND
VIN
7
BOOT
6
SW
5
PGND
9
SOP-8 (Exposed Pad)
is a registered trademark of Richtek Technology Corporation.
DS7235/36/39/40-08
January 2017
RT7235/36/39/40
Functional Pin Description
Pin No.
Pin Name
TSSOP-14
SOP-8
WDFN-10L 3x3
(Exposed Pad)
(Exposed Pad)
1
--
--
Pin Function
VS
Output Voltage Sense Input.
2
2
2
FB
Feedback Voltage Input. It is used to regulate the
output of the converter to a set value via an external
resistive voltage divider. The feedback threshold
voltage is 0.765V typically.
3
3
3
VREG5
Internal Regulator Output. Connect a 1F capacitor
to GND to stabilize output voltage.
4
4
4
SS
Soft-Start Time Setting. Connect an external capacitor
between this pin and GND to set the soft- start time.
5
--
--
GND
Analog Ground.
6
5
--
PGOOD
Open Drain Power Good Indicator Output.
7
1
1
EN
Enable Control Input. A logic-high enables the
converter; a logic-low forces the IC into shutdown
mode reducing the supply current to less than 10A.
8, 9, 15
11
5, 9
PGND
(Exposed pad) (Exposed pad) (Exposed Pad)
Power Ground. The exposed pad must be soldered
to a large PCB and connected to PGND for
maximum power dissipation.
10, 11
6, 7
6
SW
Switch Node. Connect this pin to an external L-C
filter.
12
8
7
BOOT
Bootstrap Supply for High Side Gate Driver. Connect
a 0.1F capacitor between the BOOT and SW pin.
13
9, 10
8
VIN
Power Input. The input voltage range is from 4.5V to
18V. Must bypass with a suitably large (10F x 2)
ceramic capacitor.
14
--
--
VCC
Supply Voltage Input for Internal Linear Regulator to
the Control Circuitry.
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
DS7235/36/39/40-08
January 2017
is a registered trademark of Richtek Technology Corporation.
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3
RT7235/36/39/40
Function Block Diagram
VCC*
EN
POR &
Reg
VBIAS
BOOT
VREG5
Min.
Off-Time
VREG5
VIN
VREF
OC
Control
Driver
SW
UV & OV
PGND
SW
VREG5
ZC
Ripple
Gen.
GND*
6µA
SS
VIN
FB
VS*
FB
+
Comparator
FB
0.9 x VREF
Comparator
-
PGOOD*
+
On-Time
* : VCC pin for TSSOP-14 (Exposed Pad) only.
GND pin for TSSOP-14 (Exposed Pad) only.
VS pin for TSSOP-14 (Exposed Pad) only.
PGOOD pin for TSSOP-14 (Exposed Pad) and WDFN-10L 3x3 only.
Operation
The RT7235/36/39/40 is a synchronous step-down
converter with advanced constant on-time control mode.
Using the ACOTTM control mode can reduce the output
capacitance and provide fast transient response. It can
minimize the component size without additional external
compensation network.
Current Protection
The inductor current is monitored via the internal switches
in cycle-by-cycle. Once the output voltage drops under
UV threshold, the device will enter latch mode for TSSOP14 (Exposed Pad), and hiccup mode for WDFN-10L 3x3.
UVLO Protection
Power Good
(for TSSOP-14 (Exposed Pad) and WDFN-10L 3x3 only)
After soft-start is finished, the power good function will be
activated. When the FB is activated, the PGOOD will
become an open-drain output. If the FB is below, the
PGOOD pin will be pulled low.
To protect the chip from operating at insufficient supply
voltage, the UVLO is needed. When the input voltage of
VCC is lower than the UVLO falling threshold voltage, the
device will be latch-off.
Output Discharge Control
(for TSSOP-14 (Exposed Pad) only)
Internal Regulator
The regulator provides 5V power to supply the internal
control circuit. Connecting a 1μF ceramic capacitor for
decoupling and stability is required.
When EN pin is low, the RT7235/36 will discharge the
output with an internal 50Ω MOSFET connected between
VOUT to GND pin.
Thermal Shutdown
Soft-Start
In order to prevent the converter output voltage from
overshooting during the startup period, the soft-start
function is necessary. The soft-start time is adjustable
and can be set by an external capacitor.
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When the junction temperature exceeds the OTP
threshold value, the IC will shut down the switching
operation. Once the junction temperature cools down and
is lower than the OTP lower threshold, the converter will
automatically resume switching
is a registered trademark of Richtek Technology Corporation.
DS7235/36/39/40-08
January 2017
RT7235/36/39/40
Absolute Maximum Ratings
(Note 1)
Supply Voltage, VIN, VCC --------------------------------------------------------------------------------------Switch Voltage, SW ----------------------------------------------------------------------------------------------< 10ns ---------------------------------------------------------------------------------------------------------------BOOT to SW -------------------------------------------------------------------------------------------------------EN ---------------------------------------------------------------------------------------------------------------------Other Pins -----------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
TSSOP-14 (Exposed Pad) --------------------------------------------------------------------------------------WDFN-10L 3x3 -----------------------------------------------------------------------------------------------------SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
TSSOP-14 (Exposed Pad), θJA --------------------------------------------------------------------------------WDFN-10L 3x3, θJA -----------------------------------------------------------------------------------------------WDFN-10L 3x3, θJC -----------------------------------------------------------------------------------------------SOP-8 (Exposed Pad), θJA --------------------------------------------------------------------------------------SOP-8 (Exposed Pad), θJC -------------------------------------------------------------------------------------Junction Temperature Range ------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------
Recommended Operating Conditions
−0.3V to 20V
−0.8V to (VIN + 0.3V)
−5V to 25V
−0.3V to 6V
−0.3V to 20V
−0.3V to 6V
2.50W
1.67W
2.174W
40°C/W
60°C/W
7.5°C/W
46°C/W
7°C/W
150°C
260°C
−65°C to 150°C
(Note 3)
Supply Voltage, VIN ----------------------------------------------------------------------------------------------- 4.5V to 18V
Junction Temperature Range ------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range ------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 12V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Supply Current
Shutdown Current
ISHDN
VEN = 0V
--
1
10
A
Quiescent Current
IQ
VEN = 5V, VFB = 0.8V
--
1
1.3
mA
Logic-High
1
1.15
1.25
Logic-Low
0.85
0.94
1.15
Logic Threshold
EN Input Voltage
V
VFB Voltage and Discharge Resistance
TA = 25C
0.757 0.765 0.773
TA = 40C to 85C
0.755
--
0.775
VFB = 0.8V
--
0.01
0.1
A
RDIS
VEN = 0V, VS = 0.5V
--
50
100
VREG5
6V VIN 18V, 0 < IVREG5 5mA
4.8
5.1
5.4
V
Feedback Threshold Voltage
VFB
Feedback Input Current
IFB
VOUT Discharge Resistance
V
VREG5 Output
VREG5 Output Voltage
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
DS7235/36/39/40-08
January 2017
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
RT7235/36/39/40
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Line Regulation
6V VIN 18V, IVREG5 = 5mA
--
--
20
mV
Load Regulation
0 IVREG5 5mA
--
--
100
mV
VIN = 6V, VREG5 = 4V, TA = 25C
--
70
--
mA
540
650
760
kHz
--
120
--
--
35
--
5.9
6.85
7.8
A
--
150
--
--
20
--
C
Output Current
IVREG5
Oscillation Frequency
fOSC
RDS(ON)
Switch On
Resistance
High-Side
RDS(ON)_H
Low-Side
RDS(ON)_L
(VBOOT VSW ) = 5.5V
m
Current Limit
Current Limit
ILIM
Thermal Shutdown
Thermal Shutdown Threshold
TSD
Shutdown Temperature
Thermal Shutdown Hysteresis TSD
On-Time Timer Control
On-Time
tON
VIN = 12V, VOUT = 1.05V
--
135
--
ns
Minimum On-Time
tON(MIN)
Note 5
--
55
80
ns
Minimum Off-Time
tOFF(MIN)
VFB = 0.7V
--
260
310
ns
SS Charge Current
VSS = 0V
--
6
--
A
SS Discharge Current
VSS = 0.5V
0.1
0.2
--
mA
Wake Up VREG5
3.6
3.85
4.1
0.16
0.35
0.47
VFB Rising
85
90
95
VFB Falling
--
85
--
2.5
5
--
mA
115
120
125
%
OVP Prop Delay
--
5
--
s
UVP Trip Threshold
65
70
75
UVP Hysteresis
--
10
--
UVP Prop Delay
--
250
--
s
--
tSS
x 1.7
--
ms
Soft-Start
UVLO
UVLO Threshold
Hysteresis
V
Power Good
PGOOD Threshold
PGOOD Sink Current
PGOOD = 0.5V
%
Output Under Voltage and Over Voltage Protection
OVP Trip Threshold
UVP Enable Delay
OVP Detect
tUVPEN
Relative to Soft-Start Time
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
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%
is a registered trademark of Richtek Technology Corporation.
DS7235/36/39/40-08
January 2017
RT7235/36/39/40
Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are
stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in
the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may
affect device reliability.
Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is
measured at the exposed pad of the package.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Note 5. Guaranteed by design.
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
DS7235/36/39/40-08
January 2017
is a registered trademark of Richtek Technology Corporation.
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7
RT7235/36/39/40
Typical Application Circuit
RT7235/36/39/40
VIN
C1
10µF x 2
C2
0.1µF
VIN
VCC*
BOOT
C6
0.1µF
C5
3.9nF
C7
22µF x 2
R1
8.25k
R2
22k
R3
100k
C4
1µF
C3
FB
PGOOD*
Power GOOD
VOUT
1.05V/5A
SW
EN
Input Signal
L1
1.4µH
VREG5
SS
GND*
VS*
PGND
* : VCC pin for TSSOP-14 (Exposed Pad) only.
VS pin for TSSOP-14 (Exposed Pad) only.
GND pin for TSSOP-14 (Exposed Pad) only.
PGOOD pin for TSSOP-14 (Exposed Pad) and WDFN-10L 3x3 only.
Table 1. Suggested Component Values (VIN = 12V)
V OUT (V)
R1 (k)
R2 (k)
C3 (pF)
L1 (H)
C7 (F)
1
6.81
22.1
--
1.4
22 to 68
1.05
8.25
22.1
--
1.4
22 to 68
1.2
12.7
22.1
--
1.4
22 to 68
1.8
30.1
22.1
5 to 22
2
22 to 68
2.5
49.9
22.1
5 to 22
2
22 to 68
3.3
73.2
22.1
5 to 22
2
22 to 68
5
124
22.1
5 to 22
3.3
22 to 68
7
180
22.1
5 to 22
3.3
22 to 68
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is a registered trademark of Richtek Technology Corporation.
DS7235/36/39/40-08
January 2017
RT7235/36/39/40
Typical Operating Characteristics
Efficiency vs. Output Current
Efficiency vs. Output Current
100
100
RT7236/40
90
80
80
70
70
Efficiency (%)
Efficiency (%)
RT7235/39
90
60
50
VIN = 5V
VIN = 12V
VIN = 18V
40
30
20
60
VIN = 5V
VIN = 12V
VIN = 18V
50
40
30
20
10
10
VOUT = 1.05V
0
0.001
0.01
0.1
1
VOUT = 1.05V
0
0.001
10
0.01
Output Current (A)
10
Feedback Threshold Voltage vs. Temperature
Output Voltage vs. Input Voltage
0.780
Feedback Threshold Voltage (V)
1.058
1.056
Output Voltage (V)
1
Output Current (A)
1.060
1.054
1.052
1.050
1.048
1.046
1.044
1.042
VIN = 4.5V to 18V, VOUT = 1.05V
0.775
0.770
0.765
0.760
0.755
VIN = 12V, VOUT = 1.05V, IOUT = 0A
0.750
1.040
4
6
8
10
12
14
16
-50
18
-25
0
Input Voltage (V)
RT7235/39
1.09
1.08
1.08
Output Voltage (V)
1.09
1.07
1.06
1.05
VIN = 18V
VIN = 12V
VIN = 5V
1.03
50
75
100
125
Output Voltage vs. Output Current
1.10
1.04
25
Temperature (°C)
Output Voltage vs. Output Current
1.10
Output Voltage (V)
0.1
1.02
RT7236/40
1.07
1.06
1.05
VIN = 18V
VIN = 12V
VIN = 5V
1.04
1.03
1.02
1.01
1.01
VOUT = 1.05V
1.00
VOUT = 1.05V
1.00
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Output Current (A)
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DS7235/36/39/40-08
January 2017
5
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Output Current (A)
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RT7235/36/39/40
Switching Frequency vs. Temperature
700
690
690
Switching Frequency (kHz)1
Switching Frequency (kHz)1
Switching Frequency vs. Input Voltage
700
680
670
660
650
640
630
620
610
600
680
670
660
650
640
630
620
610
600
4
6
8
10
12
14
16
18
-50
-25
0
Input Voltage (V)
50
75
100
125
Temperature (°C)
Current Limit vs. Temperature
Current Limit vs. Input Voltage
8.0
9.0
8.5
Current Limit (A)
7.5
Current Limit (A)
25
7.0
6.5
6.0
8.0
7.5
7.0
6.5
6.0
5.5
5.5
VIN = 12V, VOUT = 1.05V
5.0
5.0
-50
-25
0
25
50
75
100
125
4
8
10
12
14
16
Input Voltage (V)
Load Transient Response
Load Transient Response
RT7235/39
18
RT7235/36/39/40
VOUT
(20mV/Div)
VOUT
(20mV/Div)
IOUT
(2A/Div)
IOUT
(2A/Div)
VIN = 12V, VOUT = 1.05V, IOUT = 0A to 5A
Time (100μs/Div)
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6
Temperature (°C)
VIN = 12V, VOUT = 1.05V, IOUT = 1A to 5A
Time (100μs/Div)
is a registered trademark of Richtek Technology Corporation.
DS7235/36/39/40-08
January 2017
RT7235/36/39/40
Switching
Switching
VSW
(10V/Div)
VSW
(10V/Div)
VOUT
(5mV/Div)
VOUT
(5mV/Div)
IL
(1A/Div)
VIN = 12V, VOUT = 1.05V, IOUT = 1A
IL
(5A/Div)
Time (1μs/Div)
Time (1μs/Div)
Power On from VIN
Power Off from VIN
VIN
(10V/Div)
VIN
(10V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
IOUT
(2A/Div)
IOUT
(2A/Div)
VIN = 12V, VOUT = 1.05V, IOUT = 5A
VIN = 12V, VOUT = 1.05V, IOUT = 5A
Time (2.5ms/Div)
Time (10ms/Div)
Power On from EN
Power Off from EN
VEN
(2V/Div)
VEN
(2V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
IOUT
(5A/Div)
IOUT
(5A/Div)
VIN = 12V, VOUT = 1.05V, IOUT = 5A
Time (500μs/Div)
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
DS7235/36/39/40-08
VIN = 12V, VOUT = 1.05V, IOUT = 5A
January 2017
VIN = 12V, VOUT = 1.05V, IOUT = 5A
Time (500μs/Div)
is a registered trademark of Richtek Technology Corporation.
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RT7235/36/39/40
UVLO vs. Temperature
EN Threshold Voltage vs. Temperature
4.0
1.4
3.9
1.3
1.2
Rising
UVLO (V)
EN Threshold Voltage (V)
1.5
1.1
Falling
1.0
Rising
3.8
3.7
3.6
Falling
0.9
3.5
0.8
VIN = 12V, VOUT = 1.05V
0.7
3.4
-50
-25
0
25
50
75
100
125
-50
25
50
75
100
Temperature (°C)
Power Good from EN Turn On
Power Good from EN Turn Off
125
RT7235/36
VEN
(5V/Div)
VEN
(5V/Div)
VPGOOD
(10V/Div)
VPGOOD
(10V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
VIN = 12V, VOUT = 1.05V, IOUT = 5A
Time (250μs/Div)
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0
Temperature (°C)
RT7235/36
IOUT
(5A/Div)
-25
IOUT
(5A/Div)
VIN = 12V, VOUT = 1.05V, IOUT = 5A
Time (2.5ms/Div)
is a registered trademark of Richtek Technology Corporation.
DS7235/36/39/40-08
January 2017
RT7235/36/39/40
Application Information
The RT7235/36/39/40 is a synchronous high voltage Buck
converter that can support the input voltage range from
4.5V to 18V and the output current up to 5A. It adopts
ACOTTM mode control to provide a very fast transient
response with few external compensation components.
the EN pin can also be externally pulled high by adding a
REN resistor and CEN capacitor from the VIN pin (see Figure
1).
EN
VIN
PWM Operation
Advanced Constant On-Time Control
The RT7235/36/39/40 has a unique circuit which sets the
on-time by monitoring the input voltage and SW signal.
The circuit ensures the switching frequency operating at
650kHz over input voltage range and loading range.
Soft-Start
The RT7235/36/39/40 contains an external soft-start clamp
that gradually raises the output voltage. The soft-start
timing can be programmed by the external capacitor
between the SS and GND pins. The chip provides a 6μA
charge current for the external capacitor. If a 3.9nF
capacitor is used, the soft-start will be 0.87ms (typ.).
The available capacitance range is from 2.7nF to 220nF.
C5 (nF) 1.365
ISS ( A)
RT7235/36/39/40
GND
Figure 1. External Timing Control
An external MOSFET can be added to implement digital
control on the EN pin when no system voltage above 2V
is available, as shown in Figure 2. In this case, a 100kΩ
pull-up resistor, REN, is connected between the VIN and
EN pins. MOSFET Q1 will be under logic control to pull
down the EN pin.
VIN
REN
100k
Chip Enable Operation
The EN pin is the chip enable input. Pulling the EN pin
low (
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