Document
Buck or Buck-Boost (Inverting) Current Mode Controller
POWER MANAGEMENT Description
The SC4508A is a low voltage current mode switching regulator controller that drives a P-channel power MOSFET with programmable switching frequency. It can be configured in either buck or buck boost (inverting) converters. The converters can be operated from 2.7V to 15V input voltage range. The typical operating supply current is 3mA and a shutdown pin allows the user to turn the controller off reducing it to less than 200µA. The output voltage can adjusted by external resistor diwww.DataSheet4U.com vider. The switching frequency is programmable up to 1.5MHz, allowing small inductor and capacitor values to minimize PCB space. The operating current level is programmable via an external sense resistor. Accessible reference voltage allows users to make output voltage as low as they want.
SC4508A
Features
Wide input voltage range 2.7V to 15V Programmable output voltage Programmable switching frequency up to 1.5MHz Buck or buck boost (inverting) configuration Current mode control with slope compensation Very low quiescent current in shutdown mode Accessible reference voltage Hiccup mode after 32 cycle-by-cycle OCP 4mm x 4mm MLPQ-12 lead free package. This product is fully WEEE and RoHS compliant
Applications
Low power point of use converters Single or multiple output low power converters Positive and/or negative output voltage DSL cards Graphic cards I/O cards Negative bias supplies
Typical Application Circuits
Vin Vin
V+ V+ VREF VREF CS FB+ OUT FB-
FB+ FB-
SC4508A
SC4508A
CS
COMP
Vout SS/EN GND OSC
COMP
OUT
Vout SS/EN GND OSC
Revision: July 25, 2007
1
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SC4508A
POWER MANAGEMENT Absolute Maximum Rating
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not implied.
Parameter VDD to GND SS/EN to GND(1) FB+, FB-, COMP, OSC to GND VREF Current
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Symbol
Maximum -0.3 to 16 3.2 5 1
Units V V V mA °C/W °C/W °C °C °C
Junction to Ambient
θJ A θJ C TSTG TJ TPKG
48 3 -60 to +150 -40 to +150 260
Thermal Resistance, Junction to Case Storage Temperature Range Junction Temperature Range Peak IR Reflow Temperature 10 - 40s
Note: (1) Voltage from internal circuitry could be higher than 3.2V. See Application Information, Soft-Start section.
Electrical Characteristics
Unless specified: VDD = 12V, VFB+ = VREF, VFB- = 0, OUT = open, CVDD = 1uF, CSS/EN = 0.1uF, COSC = 330pF. TA = TJ = -40°C to 125°C
Parameter Pow er Supply Input Voltage Range Quiescent Current Operating Current Undervoltage Lockout Start Threshold UVLO Hysteresis Oscillator Frequency Range Frequency Charge Current Error Amplifier Feedback Input Voltage Offset Voltage Input Bias Current Transconductance Output Source or Sink Current
2007 Semtech Corp.
Test Conditions
Min
Typ
Max
Unit
2.7 SS/EN = low SS/EN = high, No load 200 3
15 500
V µA mA
VDD rising
2.35
2.5 100
2.55
V mV
100 450 500 100
1500 550
KHz KHz µA
-0.2 2 100 5 50
2
0.7
V mV
300
nA mS µA
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100
SC4508A
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless specified: VDD = 12V, VFB+ = VREF, VFB- = 0, OUT = open, CVDD = 1uF, CSS/EN = 0.1uF, COSC = 330pF. TA = TJ = -40°C to 125°C
Parameter PWM Comparator Maximum Duty Cycle
Test Conditions
Min
Typ
Max
Unit
C = 1.5nF, 100kHz C = 100pF, 1.5MHz
97 95 200 63 50
% % nS mV/Ts ns
Minimum On Time
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Slope Compensation
Delay to Output VREF Reference Output Voltage Output Voltage Output Current Line Regulation Load Regulation Soft Start/Enable/Shutdow n Charge Current VSS/EN > 0.9V VSS/EN < 0.9V Discharge Current Enable Logic Voltage SHDN Logic Voltage Current Limit Cycle by Cycle Threshold Consecutive Overcurrent Clock Cycles before Auto Restart Shutdown Delay to Output Output Gate Drive On-Resistance(H) Gate Drive On-Resistance(L) Gate Drive On-Resistance(H) Gate Drive On-Resistance(L) Rise Time Fall Time
2007 Semtech Corp.
0.4925 TA = 25°C, VDD = 5V 0.496
0.5 0.5
0.5075 0.504 1
V V mA mV mV
VDD = 2.7 to 15V, IVREF = 1mA VDD = 5V, IVREF = 0 to 1mA
5 2
10 4
20 10 12 2 0.35
µA
mA V V
V D D = 5V
90
110 32
130
mV
50
nS
8 8 V D D = 5V V D D = 5V COUT = 1000pF COUT = 1000pF
3
Ohm Ohm Ohm Ohm nS nS
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15 15 20 20
SC4508A
POWER MANAGEMENT Pin Configuration
TOP VIEW
VDD OSC COMP
Ordering Information
Part Number SC4508AMLTRT(2) SC4508ABUCKEVB SC4508ABUCK-BOOSTEVB P ackag e
(1)
MLPQ -12 Evaluation Board Evaluation Board
12 OUT
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11
10 9 8 7 FB+ FBPGND
1 2 3 4 5 6
CS
Notes: (1) Only available in tape and reel packaging. A reel contains 3000 devices. (2) Lead free product. This product is fully WEEE and RoHS compliant.
SS/EN
VREF
NC
AGND
(MLPQ - 12, 4mm x 4mm)
Pin Descriptions
Pin # 1 2 3 Pin Name OUT CS SS/E.