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Preliminary
RT9907
3 Channel DC/DC Converters IC with High-Efficiency Step-Up and Step-Down
General Description
The RT9907 is a three channel power-supply solution for digital still cameras and other battery-powered devices. It integrates an asynchronous step-up and two synchronous step-down DC-DC converters. The RT9907 is targeted for applications that use two AA cells or a single lithium-ion battery. The three DC-DC converters (CH1, CH2, CH3) accept input voltage from 1.5V to 5.5V. Each DC-DC converter has better transient response and excellent stability by providing current-mode control and external compensation network. With built-in Internal MOSFET and up to 1.4MHz operating frequency, the RT9907 allows minimum BOM cost and PCB area. The step-down DC-DC converters (CH2, CH3) can regulate output voltage as low as 0.8V. Three operational modes are available: PWM, PSM, Low-Dropout modes. At PWM mode, Internal synchronous rectifier with low RDS(ON) dramatically reduces conduction loss and achieve 94% efficiency. It enters Low-Dropout mode when normal PWM cannot provide regulated output voltage by continuously turning on the upper P-MOSFET. No external Schottky diode is required in practical application. Each DC-DC converter has independent enable input and soft-start function allowing versatile power sequence combination. Complete protection functions are implemented such as short circuit, over-voltage protection. The RT9907 is available in small VQFN-24L 4x4 package.
GND EN3 FB3 EN2
Features
1.5V to 5.5V Battery Input Voltage Range Main step-up DC-DC Converter 1.5V to 5.5V Adjustable Output Voltage Up to 90% Efficiency 2.6A, 0.3 Internal Power Switch Two Step-Down DC-DC Converters 0.8V to 5.5V Adjustable Output Voltage 94% Efficiency 100% Duty Cycle Up to 1.4MHz Switching Frequency 1A Supply Current in Shutdown Mode Programmable Soft Start Function Independent Enable Pin (CH1, CH2, CH3) External Compensation Network (CH1, CH2, CH3) Short Circuit Protection (CH1, CH2, CH3) Over Voltage Protection (CH2) 24-Lead VQFN Package RoHS Compliant and 100% Lead (Pb)-Free
Applications
Digital Still Camera PDAs Portable Device
Pin Configurations
(TOP VIEW)
COMP2
19 18 17 16
Ordering Information
RT9907 Package Type QV : VQFN-24L 4x4 (V-Type) Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard)
COMP3 VDD3 LX3 PGND3 SS RT
1 2 3 4 5 6
24
23
22
21
FB2
20
EN1 ENM VDD2 LX2 PGND2 LX1
GND
15 14 25 13
COMP1
FB1
VDDM
Richtek Pb-free and Green products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. 100% matte tin (Sn) plating. DS9907-07 August 2007
VQFN-24L 4x4
PGND1
VDD1
GND
Note :
7
8
9
10
11
12
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RT9907
Typical Application Circuit
1-cell Li+ Battery 3.4V to 4.2V
Preliminary
V BAT 10F 1F 8 V BAT 10F x 2 1.5V/500mA 200k 10F x 4 220k 17 Chip Enable 18 21 22 20k 10k 30k 4.7nF 1nF 1nF 1nF 100pF 4.7H VDD3 LX3 VDDM 2
10F
4.7H 0.1F
3 24
LX1 13 SS0520 VDD1 12 680k 9 5V/500mA
FB3
ENM EN1 EN2 EN3 RT9907
FB1 130k VDD2 16
10F x 4
V BAT 10F x 2
10 COMP1 19 COMP2 1 COMP3 FB2 PGND3 PGND2 PGND1 GND 5 SS RT LX2
15
4.7H
3.3V/500mA 470k 10F x 4 150k
100pF 20
6
4
14 11
7, 23, Exposed Pad (25)
Figure 1. Typical Application Circuit for 1-cell Li+ Battery
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Preliminary
2-AA Battery 1.8V to 3.2V
RT9907
1F 8 V BAT 10F x 2 1.5V/300mA 200k 10F x 4 220k 17 Chip Enable 18 21 22 20k 10k 30k 4.7nF 1nF 1nF 1nF 9 ENM EN1 EN2 EN3 15 4.7H RT9907 VDD2 16 10F x 2 LX2 2.5V/300mA 470k 10F x 4 220k FB1 150k 3.3V 100pF 4.7H VDD3 LX3 VDDM 2 4.7H SS0520 VDD1 12 470k 10F x 4 V BAT 10F x 2
3 24
LX1 13
FB3
I/O 3.3V/500mA
10 COMP1 19 COMP2 1 COMP3 FB2 PGND3 PGND2 PGND1 GND 5 SS RT
100pF 20
6
4 14 11
7, 23, Exposed Pad (25)
Figure 2. Typical Application Circuit for 2-AA Battery Supply
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RT9907
Function Block Diagram
Preliminary
VDDM
ENM
EN CH1 Current-MODE Asynchronous Step-Up PWM Boost
EN1 VDD1 LX1
PGND1 COMP1 FB1 EN2 VDD2 LX2 PGND2 COMP2 FB2 EN3 VDD3 LX3 PGND3 COMP3 FB3
SS
Soft-Start OSC
CH2 Current-MODE Synchronous Step-Down PWM Buck2
RT
PWM OSC
Thermal Shutdown
CH3 Current-MODE Synchronous Step-Down PWM Buck3
GND
ENM 0 1 1 1 1
EN1 X 0 1 1 1
EN2 X 0 0 1 1
EN3 X 0 0 0 1
CH1 Off Off On On On
CH2 Off Off Off On On
CH3 Off Off Off Off On
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Preliminary Functional Pin Description
Pin No. 1 2 3 4 5 6 7, 23 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 24 Pin Name COMP3 VDD3 LX3 PGND3 SS RT GND VDDM FB1 COMP1 PGND1 VDD1 LX1 PGND2 LX2 VDD2 ENM EN1 COMP2 FB2 EN2 EN3 FB3 CH3 Feedback Compensation Pin. Pin Function
RT9907
CH3 Power Input Pin. CH3 Switch Node. Drains of the internal P-MOSFET and N-MOSFET switches. Connect an inductor to LX3 pins together as close as possible. Power Ground for CH3. Sets the Soft Start interval of the converter. Connect a capacitor from this pin to ground. Frequency setting resistor connection pin. Frequency is 500kHz if RT pin not connected Analog Ground. Device Input Power Pin. CH1 Feedback Input Pin. CH1 Feedback Compensation Pin. Power Ground for CH1 CH1 Power Input Pin. Connect output of Boost to this pin. CH1 Switch Vode. Connect an inductor to LX1 Pins together as close as possible. Power Ground for CH2. CH2 Switch Node. Drains of the internal P-Channel and N-MOSFET switches. Connect an inductor to LX2 pins together as close as possible. CH2 Power Input Pin. Whole Device Control Pin. Tie this pin higher than 1.3V to enable the device. Tie below 0.4V to turn off the device. CH1 Enable Input. Tie this pin higher than 1.3V to enable CH1. Tie below 0.4V to turn off the CH1. CH2 Feedback Compensation Pin. CH2 Feedback Input. CH2 Enable Input. Tie this pin higher than 1.3V to enable CH2. Tie below 0.4V to turn off the CH2. CH3 Enable Input. Tie this pin higher than 1.3V to enable CH3. Tie below 0.4V to turn off the CH3. CH3 Feedback Input. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation.
Exposed Pad (25) GND
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RT9907
Absolute Maximum Ratings
Preliminary
(Note 1)
Supply Input Voltage, VDDM, VDD1, VDD2,VDD3 ------------------------------------------------------------------------------------------ -0.3 to 7V LX1 Pin Switch Voltage ------------------------------------------------------------------------------------------ -0.3V to 7V LX2 Pin Switch Voltage ------------------------------------------------------------------------------------------ -0.3V to (VDD2 + 0.3V) LX3 Pin Switch Voltage ------------------------------------------------------------------------------------------ -0.3V to (VDD3 + 0.3V) Other I/O Pin Voltage --------------------------------------------------------------------------------------------- -0.3V to (VDDM + 0.3V) Power Dissipation, PD @ TA = 25C VQFN-24L 4x4 ----------------------------------------------------------------------------------------------------- 1.85W Package Thermal Resistance (Note 3) VQFN-24L 4x4, JA ------------------------------------------------------------------------------------------------ 54C/W Junction Temperature Range ------------------------------------------------------------------------------------ 0C to 125C Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------------- 260C Operation Temperature Range ---------------------------------------------------------------------------------- -40C to 85C Storage Temperature Range ------------------------------------------------------------------------------------ -65C to 150C ESD Susceptibility (Note 2) HBM (Human Body Mode) -------------------------------------------------------------------------------------- 2kV MM (Machine Mode) ---------------------------------------------------------------------------------------------- 200V
Electrical Characteristics
(VDDM =3.3V, TA = 25C, Unless Otherwise specification)
Parameter Supply Voltage Minimum Startup Voltage (Boost) VDDM Operating Voltage VDD1, VDD2, VDD3 Operating Voltage VDDM Over Voltage Protection Supply Current Shutdown Supply Current
Symbol VST VVDDM VVDD1 VVDD2, VVDD3
Test Condition Boost loading < 1mA VDDM Pin Voltage VDD1, VDD2, VDD3 Pin Voltage
Min -2.4 1.5 --
Typ 1.5 --
Max -5.5 5.5
Units V V V V A
6.5 0.01
-1
IOFF
VENM pin=0V VVDDM = 3.3V, VFB1 = 0.9V VENM = 3.3V, VEN1 = 3.3V, VEN2 = 0V, VEN3 = 0V VVDDM = 3.3V,
--
CH1 DC/DC Converter
IVDDM
--
250
350
A
CH2 DC/DC Converter Supply Current
IVDDM
VFB2 = 0.9V VENM = 3.3V, VEN1 = 0V, VEN2 = 3.3V, VEN3 = 0V VVDDM = 3.3V,
--
250
350
A
CH3 DC/DC Converter Supply Current
IVDDM
VFB3 = 0.9V VENM = 3.3V, VEN1 = 0V, VEN2 = 0V, VEN3 = 3.3V
--
250
350
A
To be continued
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Preliminary
Parameter Oscillator Operation Frequency Range CH1 Maximum Duty Cycle CH2 Maximum Duty Cycle CH3 Maximum Duty Cycle Feedback Voltage (CH1, CH2, CH3) Feedback Voltage Feedback Voltage Error Amplifier GM Compensation Source Current Compensation Sink Current Power Switch CH1 On Resistance of MOSFET CH1 Current Limitation CH2 On Resistance of MOSFET CH2 Current Limitation CH3 On Resistance of MOSFET CH3 Current Limitation UVP Threshold Voltage @FB2, FB3 Over Voltage Protection @FB2 Control ENM, EN1, EN2, EN3 Input High Level Threshold ENM, EN1, EN2, EN3 Input Low Level Threshold Thermal Protection Thermal Shutdown Thermal Shutdown Hysteresis TSD TSD VVDDM = 3.3V VVDDM = 3.3V RDS(ON) RDS(ON) RDS(ON) N-MOSFET VVDD1 = 3.3V N-MOSFET, VVDD2 = 3.3V P-MOSFET, VVDD2 = 3.3V VVDD2 = 3.3V N-MOSFET, VVDD3 = 3.3V P-MOSFET, VVDD3 = 3.3V VVDD3 = 3.3V -2 --1.3 --1.3 0.3 0.95 -0.4 300 2.6 350 350 1.5 350 350 1.5 0.4 1 0.8 0.8 ---0.2 22 22 VFB VFB CH1, CH2, CH3 CH1, CH2, CH3 3.0V < VDDM < 5.5V 0.788 -0.8 -FOSC DMAX1 DMAX2 DMAX3 RT Open 475 ---550 85 --Symbol Test Condition Min Typ
RT9907
Max 625 90 100 100 0.812 12 Units kHz % % % V
mV
---400 3 450 450 1.9 450 450 1.9 0.5 -1.3 --
ms A A m A m m A m m A V V V V C C
UVP (CH2, CH3) & Over Voltage Protection (CH2)
140 --
180 10
---
Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. 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 for extended periods may remain possibility to affect device reliability. Note 2. Devices are ESD sensitive. Handling precaution recommended. Note 3. JA is measured in the natural convection at T A = 25C on a low effective thermal conductivity test board of JEDEC 51-3 thermal measurement standard.
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RT9907
Preliminary
Typical Operating Characteristics
Reference Voltage vs. Temperature
0.808
Oscillator Ferquency vs. RRT
1800
Oscillator Frequecny (kHz)
-50 -30 -10 10 30 50 70 90
0.806
1600 1400 1200 1000 800 600 400 200 0 0 100 200 300 400 500 600
Reference Voltage (V)
0.804 0.802 0.8 0.798 0.796 0.794 0.792
Temperature (C)
RRT (k)
Boost Efficiency vs. Output Current
100
Boost Output Voltage vs. VDD1 Voltage
3.345
VOUT = 3.3V
90
VBAT = 2.5V, VDDM = 3.3V, IOUT = 250mA VIN 3V 2.5V
3.34 3.335 3.33 3.325 3.32 3.315 3.31
80
2V 1.8V
70
60
Boost
50 1 10 100 1000
Output Voltage (V)
Efficiency (%)
3.305 1.5 2 2.5 3 3.5 4 4.5 5 5.5
Output Current (mA)
VDD1 Voltage (V)
Boost Output Voltage vs. VDDM Voltage
3.332 3.33
Boost Load Transient Response
Output Voltage Deviation (100mV/Div) Load Current (200mA/Div)
VIN = 1.8V, VOUT = 3.3V, @IOUT = 100mA to 400mA
VBAT = 2.5V, VDD1 = 3.3V, IOUT = 250mA
Output Voltage (V)
3.328 3.326 3.324 3.322 3.32 3.318 3.316 2.4 2.8 3.2 3.6 4 4.4 4.8 5.2 5.6
Time (1ms/Div)
VDDM Voltage (V)
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Preliminary
RT9907
Boost Load Transient Response
Boost Load Transient Response
Output Voltage Deviation (100mV/Div) Output Voltage Deviation (100mV/Div) Load Current (200mA/Div)
VIN = 2V, VOUT = 3.3V, @IOUT = 100mA to 400mA
Load Current (200mA/Div)
VIN = 2.5V, VOUT = 3.3V, @IOUT = 100mA to 400mA
Time (1ms/Div)
Time (1ms/Div)
Boost Load Transient Response
Output Voltage Deviation (100mV/Div)
Boost LX & Output Ripple
VIN = 1.8V, VOUT = 3.3V, @IOUT = 100mA
Load Current (200mA/Div)
VIN = 3V, VOUT = 3.3V, @IOUT = 100mA to 400mA
Time (1ms/Div)
Output Ripple (10mV/Div)
LX1 (2V/Div)
Time (1us/Div)
Boost LX & Output Ripple
VIN = 1.8V, VOUT = 3.3V, @IOUT = 300mA
Boost LX & Output Ripple
VIN = 2.5V, VOUT = 3.3V, @IOUT = 100mA
LX1 (2V/Div)
Output Ripple (10mV/Div)
Time (1us/Div)
Output Ripple (10mV/Div)
LX1 (2V/Div)
Time (1us/Div)
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RT9907
Boost LX & Output Ripple
VIN = 2.5V, VOUT = 3.3V, @IOUT = 400mA
Preliminary
Boost LX & Output Ripple
VIN = 3V, VOUT = 3.3V, @IOUT = 100mA
LX1 (2V/Div)
Output Ripple (10mV/Div)
Time (1us/Div)
Output Ripple (10mV/Div)
LX1 (2V/Div)
Time (1us/Div)
Boost LX & Output Ripple
VIN = 3V, VOUT = 3.3V, @IOUT = 400mA
Buck2 Efficiency vs. Output Current
100
VOUT = 1.5V VIN = 2.2V
90
Efficiency (%)
LX1 (2V/Div)
80
VIN = 4.5V
70
VIN = 2.5V
Output Ripple (10mV/Div)
VIN = 3V VIN = 3.8V
60
50
Time (1us/Div)
1
10
100
1000
Output Current (mA)
Buck2 Efficiency vs. Output Current
100
Buck2 Efficiency vs. Output Current
100
VOUT = 1.8V
VIN = 2.5V
VOUT = 2.5V VIN = 4.5
90
90 80
Efficiency (%)
80
VIN = 4.5 VIN = 3.8V
VIN = 3V
Efficiency (%)
70 60 50
70
VIN = 3.8V VIN = 3V
60
40 30
50 1 10 100 1000
1
10
100
1000
Output Current (mA)
Output Current (mA)
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DS9907-07 August 2007
Preliminary
RT9907
Buck2 Output Voltage vs. VDDM Voltage
1.82
Buck2 Output Voltage vs. VDD2 Voltage
1.82
VBAT = VDDM = 3.3V, IOUT = 250mA
1.818
1.818
VDD2 = 3.3V, IOUT = 250mA
Output Voltage (V)
Output Voltage (V)
1.816 1.814 1.812 1.81 1.808 1.806 1.804 2 2.5 3 3.5 4 4.5
1.816 1.814 1.812 1.81 1.808 1.806 1.804 2 2.5 3 3.5 4 4.5 5 5.5 6
VDD2 Voltage (V)
VDDM Voltage (V)
Buck2 Load Transient Response
@IOUT = 100mA to 400mA
Buck2 Load Transient Response
@IOUT = 100mA to 400mA
Output Voltage Deviation (100mV/Div)
Load Current (200mA/Div)
VDD2 = 2.5V, VDDM = 3.3V, VOUT = 1.8V
Load Current (200mA/Div)
Output Voltage Deviation (100mV/Div)
VDD2 = 3V, VDDM = 3.3V, VOUT = 1.8V
Time (1ms/Div)
Time (1ms/Div)
Buck2 Load Transient Response
Output Voltage Deviation (100mV/Div) Output Voltage Deviation (100mV/Div)
@IOUT = 100mA to 400mA
Buck2 Load Transient Response
@IOUT = 100mA to 400mA
Load Current (200mA/Div)
VDD2 = 3.8V, VDDM = 3.3V, VOUT = 1.8V
Load Current (200mA/Div)
VDD2 = 4.5V, VDDM = 3.3V, VOUT = 1.8V
Time (1ms/Div)
Time (1ms/Div)
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RT9907
Buck2 LX & Output Ripple
@IOUT = 500mA
Preliminary
Buck2 LX & Output Ripple
@IOUT = 250mA
LX2 (2V/Div)
Output Ripple (10mV/Div)
Output Ripple (10mV/Div)
LX2 (2V/Div)
VDD2 = 2.5V, VDDM = 3.3V, VOUT = 1.8V VDD2 = 2.5V, VDDM = 3.3V, VOUT = 1.8V
Time (500ns/Div)
Time (500ns/Div)
Buck2 LX & Output Ripple
Buck2 LX & Output Ripple
LX2 (2V/Div)
Output Ripple (10mV/Div)
@IOUT = 250mA VDD2 = 3V, VDDM = 3.3V, VOUT = 1.8V
Output Ripple (10mV/Div)
LX2 (2V/Div)
@IOUT = 500mA VDD2 = 3V, VDDM = 3.3V, VOUT = 1.8V
Time (500ns/Div)
Time (500ns/Div)
Buck2 LX & Output Ripple
Buck2 LX & Output Ripple
LX2 (2V/Div)
Output Ripple (10mV/Div)
@IOUT = 250mA VDD2 = 3.8V, VDDM = 3.3V, VOUT = 1.8V
Output Ripple (10mV/Div)
LX2 (2V/Div)
@IOUT = 500mA VDD2 = 3.8V, VDDM = 3.3V, VOUT = 1.8V
Time (500ns/Div)
Time (500ns/Div)
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DS9907-07 August 2007
Preliminary
RT9907
Buck2 LX & Output Ripple
Buck2 LX & Output Ripple
LX2 (2V/Div)
Output Ripple (10mV/Div)
@IOUT = 250mA VDD2 = 4.5V, VDDM = 3.3V, VOUT = 1.8V
Output Ripple (10mV/Div)
LX2 (2V/Div)
@IOUT = 500mA VDD2 = 4.5V, VDDM = 3.3V, VOUT = 1.8V
Time (500ns/Div)
Time (500ns/Div)
Buck3 Efficiency vs. Output Current
100
Buck3 Efficiency vs. Output Current
100
VOUT = 1.5V
VIN = 2.2V
90
VOUT = 1.8V
VIN = 2.5V
90
Efficiency (%)
Efficiency (%)
80
VIN = 4.5V VIN = 3V VIN = 3.8V VIN = 2.5V
80
VIN = 4.5V VIN = 3.8V VIN = 3V
70
70
60
60
50 1 10 100 1000
50 1 10 100 1000
Output Current (mA)
Output Current (mA)
Buck3 Efficiency vs. Output Current
100
Buck3 Output Voltage vs. VDD3 Voltage
1.806
VOUT = 2.5V
90
VBAT = VDDM = 3.3V, IOUT = 250mA
1.804
VIN = 4.5V
Output Voltage (V)
100 1000
80
1.802 1.8 1.798 1.796 1.794 1.792 1.79
Efficiency (%)
70
VIN = 3.8V
60 50 40 30 1 10
VIN = 3V
2
2.5
3
3.5
4
4.5
Output Current (mA)
VDD3 Voltage (V)
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RT9907
Preliminary
Buck3 Output Voltage vs. VDDM Voltage
1.806 1.804
Buck3 Load Transient Response
Output Voltage Deviation (100mV/Div) Load Current (200mA/Div)
@IOUT = 100mA to 400mA
VDD3 = 3.3V, IOUT = 250mA
1.802 1.8 1.798 1.796 1.794 1.792 1.79 2 2.5 3 3.5 4 4.5 5 5.5 6
Output Voltage (V)
VDD3 = 2.5V, VDDM = 3.3V, VOUT = 1.8V
Time (1ms/Div)
VDDM Voltage (V)
Buck3 Load Transient Response
Output Voltage Deviation (100mV/Div) Output Voltage Deviation (100mV/Div)
@IOUT = 100mA to 400mA
Buck3 Load Transient Response
@IOUT = 100mA to 400mA
Load Current (200mA/Div)
VDD3 = 3V, VDDM = 3.3V, VOUT = 1.8V
Load Current (200mA/Div)
VDD3 = 3.8V, VDDM = 3.3V, VOUT = 1.8V
Time (1ms/Div)
Time (1ms/Div)
Buck3 Load Transient Response
@IOUT = 100mA to 400mA
Buck3 LX & Output Ripple
@IOUT = 250mA
Output Voltage Deviation (100mV/Div)
Load Current (200mA/Div)
VDD3 = 4.5V, VDDM = 3.3V, VOUT = 1.8V
Output Ripple (10mV/Div)
LX3 (2V/Div)
VDD3 = 2.5V, VDDM = 3.3V, VOUT = 1.8V
Time (1ms/Div)
Time (500ns/Div)
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DS9907-07 August 2007
Preliminary
RT9907
Buck3 LX & Output Ripple
@IOUT = 250mA
Buck3 LX & Output Ripple
@IOUT = 500mA
LX3 (2V/Div)
Output Ripple (10mV/Div)
VDD3 = 2.5V, VDDM = 3.3V, VOUT = 1.8V
LX3 Output Ripple (10mV/Div) (2V/Div)
VDD3 = 3V, VDDM = 3.3V, VOUT = 1.8V
Time (500ns/Div)
Time (500ns/Div)
Buck3 LX & Output Ripple
@IOUT = 500mA
Buck3 LX & Output Ripple
@IOUT = 250mA
LX3 Output Ripple (10mV/Div) (2V/Div)
VDD3 = 3V, VDDM = 3.3V, VOUT = 1.8V
LX3 Output Ripple (10mV/Div) (2V/Div)
VDD3 = 3.8V, VDDM = 3.3V, VOUT = 1.8V
Time (500ns/Div)
Time (500ns/Div)
Buck3 LX & Output Ripple
@IOUT = 500mA
Buck3 LX & Output Ripple
LX3 (2V/Div)
Output Ripple (10mV/Div)
LX3 Output Ripple (10mV/Div) (2V/Div)
VDD3 = 3.8V, VDDM = 3.3V, VOUT = 1.8V
@IOUT = 250mA VDD2 = 4.5V, VDDM = 3.3V, VOUT = 1.8V
Time (500ns/Div)
Time (500ns/Div)
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RT9907
Buck3 LX & Output Ripple
@IOUT = 500mA
Preliminary
Output Ripple (10mV/Div)
LX3 (2V/Div)
VDD2 = 4.5V, VDDM = 3.3V, VOUT = 1.8V
Time (500ns/Div)
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DS9907-07 August 2007
Preliminary Application Information
The RT9907 is a three-channel DC/DC converter with one voltage detector for digital still cameras and other handheld device. The three channels DC/DC converters are as follows: CH1: Step-up, asynchronous current mode DC/DC converter with an internal power MOSFET, current limit protection and high efficiency control for wide loading range CH2: Step-down, synchronous current mode DC/DC converter with internal power MOSFETs, current limit, short-circuit , over voltage protection and high efficiency control for wide loading range. CH3: Step-down, synchronous current mode DC/DC converter with internal power MOSFETs, current limit, short-circuit protection and high efficiency control for wide loading range. Soft-Start CH1, CH2 and CH3 can be soft-started individually every time when the channel is enabled. Soft-start is achieved by ramping up the voltage reference of each channel's input of error amplifier. Adding a capacitor on SS pin to ground sets the ramping up speed of each voltage reference. Triangle wave will be appeared on SS pin, which provides a clock base for soft-start. The soft-start timing would be setted by following formular. TSS = 10 x Oscillator The internal oscillator synchronizes CH1, CH2 and CH3 PWM operation frequency. The operation frequency is set by a resistor between RT pin to ground, ranging from 550kHz to 1.4MHz. Step-up (Boost) DC/DC Converter (CH1) The step-up channel (CH1) is designed as current-mode DC/DC PWM converters with built-in internal power MOS and external Schottky diode. Output voltage is regulated and adjustable up to 5.5V. This channel typically supplies 3.3V for main system power. At light load, efficiency is enhanced by pulse-skipping CSS (ms) 1nF
RT9907
mode. In this mode, the NMOS turns on by a constant pulse width. As loading increased, the converter operates at constant frequency PWM mode. The max. duty of the constant frequency is 80% for the boost to prevent high input current drawn from input.
Protection
Current limit The current of NMOS is sensed cycle by cycle to prevent over current. If the current is higher than 2.6A (typical), then the NMOS is off . This state is latched and then reset automatically at next clock cycle. Under Voltage The status of under voltage is decided by comparing FB1 voltage with 0.4V. This function is enabled after soft start finishes. If the FB1 voltage is less than 0.4V, then the NMOS will be turned off immediately. And this state is latched. After a dummy count period, the controller begins a re-soft-start procedure. If the status of under voltage remains after 4 successive times of soft-start, then CH1 is latched. Over Voltage The over voltage protection is used when the output of CH1 supplies the power of the main chip. If the output voltage of CH1 is over 6.5V, the main chip is shutdown and the NMOS is kept off. Step-Down (Buck) DC/DC Converter (CH2, CH3) The step-down channels (CH2, CH3) are designed as synchronous current-mode DC/DC PWM converters. Output voltage is regulated and adjustable down to 0.8V. The internal synchronous power switches eliminate the typical Schottky free wheeling diode and improve efficiency. At light load, efficiency is enhanced by pulse-skipping mode. In this mode, the high-side PMOS turns on by a constant pulse width. As loading increased, the converter operates at constant frequency PWM mode. While the input voltage is close to output voltage, the converter enters low dropout mode. Duty could be as long as 100% to extend battery life.
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DS9907-07 August 2007
RT9907
Protection
Current limit (CH2, CH3)
Preliminary
Thermal Protection Thermal protection function is integrated in the chip. When the chip temperature is higher than 178 degree C, the controllers of CH1, CH2, and CH3 are shutdown. 10 degree C is the hysteresis range of temperature to prevent unstable operation when the thermal protection happens. When the thermal protection is relieved, the chip operates well again.
The current of high-side PMOS is sensed cycle by cycle to prevent over current. If the current is higher than 1.5A (typical), then the high-side PMOS is off and the low-side NMOS is on. This state is latched and then reset automatically at next clock cycle. Under Voltage (CH2, CH3) The status of under voltage is decided by comparing FB2 (or FB3) voltage with 0.4V. This function is enabled after soft start finishes. If the FB2 (or FB3) voltage is less than 0.4V, then the high/low-side Power MOS are turned off immediately. And this state is latched. After a dummy count period, the CH2 (or CH3) begins a soft-start procedure. However, if the status of under voltage remains after 3 successive times of soft-start, then CH2 (or CH3) is latched.
UV remain after 3 How to reset? successive soft-start CH2 CH2 is latched, and whole Toggle ENM IC is shut down CH3 CH3 is latched Toggle EN3 or ENM
Over Voltage Protection (CH2) Over voltage protection (OVP) is used to protect the external parts connected to the output of CH2. If the FB2 voltage is higher than 1V, the high-side PMOS is off and low-side NMOS is on. This status is latched and could be reset by toggling ENM. Reference The chip has an internal 0.8V reference voltage, which is the inputs of the error amplifiers of the CH1, CH2, and CH3 to compare the difference of feedback voltage. The reference voltage can be set up stably when the supplied power (VDDM) is above 1.5V, and EN1 (or EN2, EN3) goes high.
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DS9907-07 August 2007
Preliminary Outline Dimension
D2
RT9907
D
SEE DETAIL A L 1
E
E2
1 2
1 2
e A A3 A1
b
DETAIL A Pin #1 ID and Tie Bar Mark Options Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated.
Symbol A A1 A3 b D D2 E E2 e L
Dimensions In Millimeters Min 0.800 0.000 0.175 0.180 3.950 2.300 3.950 2.300 0.500 0.350 0.450 Max 1.000 0.050 0.250 0.300 4.050 2.750 4.050 2.750
Dimensions In Inches Min 0.031 0.000 0.007 0.007 0.156 0.091 0.156 0.091 0.020 0.014 0.018 Max 0.039 0.002 0.010 0.012 0.159 0.108 0.159 0.108
V-Type 24L QFN 4x4 Package
Richtek Technology Corporation
Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611
Richtek Technology Corporation
Taipei Office (Marketing) 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (8862)89191466 Fax: (8862)89191465 Email: marketing@richtek.com
DS9907-07 August 2007
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